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Chowdhury S, Crocker NA, Peebles WA, Rhodes TL, Zeng L, Lantsov R, Van Compernolle B, Brookman M, Pinsker RI, Lau C. A novel Doppler backscattering (DBS) system to simultaneously measure radio frequency plasma fluctuations and low frequency turbulence. Rev Sci Instrum 2023; 94:073504. [PMID: 37493501 DOI: 10.1063/5.0149654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 07/12/2023] [Indexed: 07/27/2023]
Abstract
A novel quadrature Doppler Backscattering (DBS) system has been developed and optimized for the E-band (60-90 GHz) frequency range using either O-mode or X-mode polarization in DIII-D plasmas. In general, DBS measures the amplitude of density fluctuations and their velocity in the lab frame. The system can simultaneously monitor both low-frequency turbulence (f < 10 MHz) and radiofrequency plasma density fluctuations over a selectable frequency range (20-500 MHz). Detection of high-frequency fluctuations has been demonstrated for low harmonics of the ion cyclotron frequency (e.g., 2fci ∼ 23 MHz) and externally driven high-frequency helicon waves (f = 476 MHz) using an adjustable frequency down conversion system. Importantly, this extends the application of DBS to a high-frequency spectral domain while maintaining important turbulence and flow measurement capabilities. This unique system has low phase noise, good temporal resolution (sub-millisecond), and excellent wavenumber coverage (kθ ∼ 1-20 cm-1 and kr ≲ 30 cm-1). As a demonstration, localized internal DIII-D plasma measurements are presented from turbulence (f ≤ 5 MHz), Alfvenic waves (f ∼ 6.5 MHz), ion cyclotron waves (f ≥ 20 MHz), as well as fluctuations around 476 MHz driven by an external high-power 476 MHz helicon wave antenna. In the future, helicon measurements will be used to validate GENRAY and AORSA modeling tools for prediction of helicon wave propagation, absorption, and current drive location for the newly installed helicon current drive system on DIII-D.
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Affiliation(s)
- S Chowdhury
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - N A Crocker
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - L Zeng
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - R Lantsov
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - B Van Compernolle
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - M Brookman
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - R I Pinsker
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - C Lau
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
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2
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Wang G, Rhodes TL, Peebles WA. Analysis method for calculating radial correlation length of electron temperature turbulence from correlation electron cyclotron emission radiometer. Rev Sci Instrum 2022; 93:113511. [PMID: 36461495 DOI: 10.1063/5.0101680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Accepted: 09/01/2022] [Indexed: 06/17/2023]
Abstract
The radial correlation length (Lr) is one of the essential quantities to measure in order to more fully characterize and understand turbulence and anomalous transport in magnetic fusion plasmas. The analysis method for calculating Lr of electron temperature (Te) turbulence from correlation electron cyclotron emission (correlation ECE or CECE) radiometer measurements has not been fully developed partly due to the fact that the turbulent electron temperature fluctuations are generally imbedded in much larger amplitude thermal noise, which leads to a greatly reduced cross correlation coefficient (ϱ) between two spatially separated ECE signals. This work finds that this ϱ reduction factor due to thermal noise is a function of the local relative temperature fluctuation power and CECE system bandwidths of intermediate and video frequencies, independent of radial separations. This indicates that under the approximation of constant relative temperature fluctuation power for a small radial range of local CECE measurements, the original shape of ϱ as a function of radial separation without thermal noise is preserved in the CECE data with thermal noise present. For Te turbulence with a Gaussian radial wavenumber spectrum, a fit function using the product of Gaussian and sinusoidal functions is derived for calculating Lr. This analysis method has been numerically tested using simulated ECE radiometer data over a range of parameters. Using this method, the experimental temperature turbulence correlation length Lr in a DIII-D L-mode plasma is found to be ∼10 times the local ion gyroradius.
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Affiliation(s)
- G Wang
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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3
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Rhodes TL, Michael CA, Shi P, Scannell R, Storment S, Pratt Q, Lantsov R, Fitzgerald I, Hall-Chen VH, Crocker NA, Peebles WA. Design elements and first data from a new Doppler backscattering system on the MAST-U spherical tokamak. Rev Sci Instrum 2022; 93:113549. [PMID: 36461471 DOI: 10.1063/5.0101848] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 09/25/2022] [Indexed: 06/17/2023]
Abstract
A new Doppler backscattering (DBS) system has been installed and tested on the MAST-U spherical tokamak. It utilizes eight simultaneous fixed frequency probe beams (32.5, 35, 37.5, 40, 42.5, 45, 47.5, and 50 GHz). These frequencies provide a range of radial positions from the edge plasma to the core depending on plasma conditions. The system utilizes a combination of novel features to provide remote control of the probed density wavenumber, the launched polarization (X vs O-mode), and the angle of the launched DBS to match the magnetic field pitch angle. The range of accessible density turbulence wavenumbers (kθ) is reasonably large with normalized wavenumbers kθρs ranging from ≤0.5 to 9 (ion sound gyroradius ρs = 1 cm). This wavenumber range is relevant to a variety of instabilities believed to be important in establishing plasma transport (e.g., ion temperature gradient, trapped electron, electron temperature gradient, micro-tearing, kinetic ballooning modes). The system is specifically designed to address the requirement of density fluctuation wavevector alignment which can significantly reduce the SNR if not accounted for.
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Affiliation(s)
- T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - C A Michael
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - P Shi
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
| | - R Scannell
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
| | - S Storment
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - Q Pratt
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - R Lantsov
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - I Fitzgerald
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
| | - V H Hall-Chen
- Institute of High Performance Computing, Singapore 138632, Singapore
| | - N A Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
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4
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Hall-Chen VH, Damba J, Parra FI, Pratt QT, Michael CA, Peng S, Rhodes TL, Crocker NA, Hillesheim JC, Hong R, Ni S, Peebles WA, Png CE, Ruiz Ruiz J. Validating and optimizing mismatch tolerance of Doppler backscattering measurements with the beam model (invited). Rev Sci Instrum 2022; 93:103536. [PMID: 36319398 DOI: 10.1063/5.0101805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 09/07/2022] [Indexed: 06/16/2023]
Abstract
We use the beam model of Doppler backscattering (DBS), which was previously derived from beam tracing and the reciprocity theorem, to shed light on mismatch attenuation. This attenuation of the backscattered signal occurs when the wavevector of the probe beam's electric field is not in the plane perpendicular to the magnetic field. Correcting for this effect is important for determining the amplitude of the actual density fluctuations. Previous preliminary comparisons between the model and Mega-Ampere Spherical Tokamak (MAST) plasmas were promising. In this work, we quantitatively account for this effect on DIII-D, a conventional tokamak. We compare the predicted and measured mismatch attenuation in various DIII-D, MAST, and MAST-U plasmas, showing that the beam model is applicable in a wide variety of situations. Finally, we performed a preliminary parameter sweep and found that the mismatch tolerance can be improved by optimizing the probe beam's width and curvature at launch. This is potentially a design consideration for new DBS systems.
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Affiliation(s)
- V H Hall-Chen
- Institute of High Performance Computing, Singapore 138632, Singapore
| | - J Damba
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - F I Parra
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA
| | - Q T Pratt
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - C A Michael
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - S Peng
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - N A Crocker
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - J C Hillesheim
- UKAEA/CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
| | - R Hong
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - S Ni
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - C E Png
- Institute of High Performance Computing, Singapore 138632, Singapore
| | - J Ruiz Ruiz
- Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
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5
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Hong R, Rhodes TL, Wang G, Peebles WA. Ray-tracing analysis for cross-polarization scattering diagnostic on MAST-upgrade spherical tokamak. Rev Sci Instrum 2021; 92:063505. [PMID: 34243511 DOI: 10.1063/5.0043600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2021] [Accepted: 05/19/2021] [Indexed: 06/13/2023]
Abstract
A combined Doppler backscattering/cross-polarization scattering (DBS/CPS) system is being deployed on MAST-U for simultaneous measurements of local density turbulence, turbulence flows, and magnetic turbulence. In this design, CPS shares the probing beam with the DBS and uses a separate parallel-viewing receiver system. In this study, we utilize a modified GENRAY 3D ray-tracing code to simulate the propagation of the probing and scattered beams. The contributions of different scattering locations along the entire beam trajectories are considered, and the corresponding local B̃ wavenumbers are estimated using the wavevector matching criterion. The wavenumber ranges of the local B̃ that are detectable to the CPS system are explored for simulated L- and H-mode plasmas.
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Affiliation(s)
- R Hong
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
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Wang G, Rhodes TL, Peebles WA. New, improved analysis of correlation ECE data to accurately determine turbulent electron temperature spectra and magnitudes (invited). Rev Sci Instrum 2021; 92:043523. [PMID: 34243388 DOI: 10.1063/5.0041858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2020] [Accepted: 03/23/2021] [Indexed: 06/13/2023]
Abstract
Turbulent electron temperature fluctuation measurement using a correlation electron cyclotron emission (CECE) radiometer has become an important diagnostic for studying energy transport in fusion plasmas, and its use is widespread in tokamaks (DIII-D, ASDEX Upgrade, Alcator C-Mod, Tore Supra, EAST, TCV, HL-2A, etc.). The CECE diagnostic typically performs correlation analysis between two closely spaced (within the turbulent correlation length) ECE channels that are dominated by uncorrelated thermal noise emission. This allows electron temperature fluctuations embedded in the thermal noise to be revealed and fluctuation level and spectra determined. We have demonstrated a new, improved CECE coherency-based analysis for calculating the temperature fluctuation frequency spectrum and level, which has been verified both numerically through the simulation of synthetic ECE radiometer data and through analysis of experimental data from the CECE system on DIII-D. The new formulation places coherency-based analysis on a firm foundational footing and corrects some currently published methodologies. This new method accurately accounts for bias error in the coherence function and correctly calculates noise levels for a fixed data record length. It provides excellent accuracy in determining temperature fluctuation level (e.g., <10% error) even for a small realization number in the ensemble average. The method also has a smaller uncertainty (i.e., error bar) in the power spectrum when compared to the more standard cross-power method when evaluated at low coherency. Direct calculation of system noise level using correlation between randomized intermediate frequency signals is recommended.
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Affiliation(s)
- G Wang
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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7
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Zeng L, Crocker NA, Rhodes TL, Peebles WA. New methodology for measuring electron density perturbations caused by plasma coherent modes using profile reflectometry: Magnitudes and radial profiles in DIII-D. Rev Sci Instrum 2021; 92:043550. [PMID: 34243375 DOI: 10.1063/5.0043121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 04/06/2021] [Indexed: 06/13/2023]
Abstract
New capabilities of fast-sweep frequency-modulated profile reflectometry are explored to measure electron density ne perturbation magnitudes and radial profiles due to plasma coherent modes in DIII-D. The first approach is based on the frequency analysis of phase perturbations associated with high frequency (∼MHz) Alfvén eigenmodes (AEs). The measurement of ∼5.5 MHz fast-ion-driven global Alfvén eigenmodes (GAEs) is demonstrated in a neutral beam-heated DIII-D plasma. The GAE induced a broad radial distribution of phase perturbations in the profile reflectometer data. Analysis of these data determined the effective cutoff location displacement and the estimated ne fluctuation profile. In the second approach, high resolution ne profiles are used directly to determine the radial structure of ne perturbations due to a neo-classical tearing mode. These new measurements broaden the application of profile reflectometry and advance the development of AE spectroscopy as a tool for non-invasive diagnosis of fast-ion-driven modes in DIII-D and burning plasmas such as ITER.
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Affiliation(s)
- L Zeng
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - N A Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
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8
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Muscatello CM, Anderson JP, Boivin RL, Finkenthal DK, Gattuso A, Kramer GJ, LeSher M, Mrazkova TJ, Neilson GH, Peebles WA, Rhodes TL, Robinson JT, Torreblanca H, Zeller K, Zeng L, Zolfaghari A. Performance demonstration of vacuum microwave components critical for the operation of the ITER low-field side reflectometer. Rev Sci Instrum 2021; 92:033524. [PMID: 33820017 DOI: 10.1063/5.0040255] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 02/21/2021] [Indexed: 06/12/2023]
Abstract
Final design studies in preparation for manufacturing have been performed for functional components of the vacuum portion of the ITER Low-Field Side Reflectometer (LFSR). These components consist of an antenna array, electron cyclotron heating (ECH) protection mirrors, phase calibration mirrors, and vacuum windows. Evaluation of these components was conducted at the LFSR test facility and DIII-D. The antenna array consists of six corrugated-waveguide antennas for simultaneous profile, fluctuation, and Doppler measurements. A diffraction grating, incorporated into the plasma-facing miter bend, provides protection of sensitive components from stray ECH at 170 GHz. For in situ phase calibration of the LFSR profile reflectometer, an embossed mirror is incorporated into the adjacent miter bend. Measurements of the radiated beam profile indicate that these components have a small, acceptable effect on mode conversion and beam quality. Baseline transmission characteristics of the dual-disk vacuum window are obtained and are used to guide ongoing developments. Preliminary simulations indicate that a surface-relief structure on the window surfaces can greatly improve transmission. The workability of real-time phase measurements was demonstrated on the DIII-D profile reflectometer. The new automated real-time analysis agrees well with the standard post-processing routine.
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Affiliation(s)
- C M Muscatello
- General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA
| | - J P Anderson
- General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA
| | - R L Boivin
- General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA
| | - D K Finkenthal
- Palomar Scientific Instruments, San Marcos, California 92069, USA
| | - A Gattuso
- General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA
| | - G J Kramer
- Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451, USA
| | - M LeSher
- General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA
| | - T J Mrazkova
- Palomar Scientific Instruments, San Marcos, California 92069, USA
| | - G H Neilson
- Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451, USA
| | - W A Peebles
- University of California, Los Angeles, 475 Portola Plaza, Los Angeles, California 90095-1547, USA
| | - T L Rhodes
- University of California, Los Angeles, 475 Portola Plaza, Los Angeles, California 90095-1547, USA
| | - J T Robinson
- Virginia Commonwealth University, 907 Floyd Ave., Richmond, Virginia 23284, USA
| | - H Torreblanca
- CompX, P.O. Box 2672, Del Mar, California 92014-5672, USA
| | - K Zeller
- General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA
| | - L Zeng
- University of California, Los Angeles, 475 Portola Plaza, Los Angeles, California 90095-1547, USA
| | - A Zolfaghari
- Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451, USA
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9
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Kubota S, Majeski R, Boyle DP, Kaita R, Kozub T, Lantsov R, Merino E, Nguyen XV, Peebles WA, Rhodes TL. Millimeter-wave interferometry and far-forward scattering for density fluctuation measurements on LTX- β. Rev Sci Instrum 2018; 89:10H114. [PMID: 30399948 DOI: 10.1063/1.5039418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 06/19/2018] [Indexed: 06/08/2023]
Abstract
The λ ≈ 1 mm (f = 288 GHz) interferometer for the Lithium Tokamak Experiment-β (LTX-β) will use a chirped-frequency source and a centerstack-mounted retro-reflector mirror to provide electron line density measurements along a single radial chord at the midplane. The interferometer is unique in the use of a single source (narrow-band chirped-frequency interferometry) and a single beam splitter for separating and recombining the probe and reference beams. The current work provides a documentation of the interferometry hardware and evaluates the capabilities of the system as a far-forward collective scattering diagnostic. As such, the current optical setup is estimated to have a detection range of 0.4 ≲ k ⊥ ≲ 1.7 cm-1, while an improved layout will extend the upper k ⊥ limit to ∼3 cm-1. Measurements with the diagnostic on LTX are presented, showing interferometry results and scattered signal data. These diagnostics are expected to provide routine measurements on LTX-β for high frequency coherent density oscillations (e.g., Alfvénic modes during neutral beam injection) as well as for broadband turbulence.
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Affiliation(s)
- S Kubota
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - R Majeski
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - D P Boyle
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - R Kaita
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - T Kozub
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - R Lantsov
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - E Merino
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - X V Nguyen
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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10
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Sung C, Rhodes TL, Peebles WA. Turbulence measurements on the high and low magnetic field side of the DIII-D tokamak. Rev Sci Instrum 2018; 89:10H106. [PMID: 30399653 DOI: 10.1063/1.5036520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 05/30/2018] [Indexed: 06/08/2023]
Abstract
In this paper, we address the challenging question of measuring turbulence levels on the high magnetic field side (HFS) of tokamak plasmas. Although turbulence measurements on the HFS can provide a stringent constraint for the turbulence model validation, to date only low magnetic field side (LFS) measured turbulence has been used in validation studies. To address this issue, an eight channel Correlation Electron Cyclotron Emission (CECE) system at DIII-D was modified to probe both LFS and HFS. In contrast to the second harmonic extraordinary mode electron cyclotron resonance emission that is typically used in CECE, we show that it is possible to probe the HFS using fundamental O-mode electron cyclotron resonance emission. The required hardware modifications for the HFS measurements are presented here, and the potential issues in this measurement are discussed.
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Affiliation(s)
- C Sung
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
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11
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Zeng L, Wang G, Rhodes TL, Peebles WA, Sung C, Lantsov R. A free-standing wire scattering technique to monitor calibration variations of the DIII-D density profile reflectometer. Rev Sci Instrum 2018; 89:10H112. [PMID: 30399744 DOI: 10.1063/1.5036581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 06/11/2018] [Indexed: 06/08/2023]
Abstract
Real-time phase calibration of the ITER profile reflectometer is essential due to the long plasma duration and expected waveguide path length changes during a discharge. Progress has been recently made in addressing this issue by employing a phase calibration technique on DIII-D that monitors calibration variations that occur during each plasma discharge. By installing a thin free-standing metallic wire (1 mm diameter) near the end of the overmoded waveguide transmission system (oriented perpendicular to the waveguide axis), the round-trip phase shift from the wire is detected simultaneously with the plasma phase shifts. Variations in the reflectometer round trip path length (∼26 m) are then calculated after each DIII-D plasma discharge, allowing the calibration phase to be accurately monitored and updated. The round-trip reflectometer path length is observed to vary by ∼3 mm (root mean square value) during a typical DIII-D discharge. Using the variations in calibration phase, the density profile measurement accuracy can be improved. Since the wire retro-reflected power is ∼0.01 of the plasma signal, minimal effect is observed on the reflected signal from the plasma. Importantly, through a suitable choice in wire diameter, the calibration signal can be made approximately independent of the V-band reflectometer launch polarization. This is particularly important on DIII-D since orthogonal X- and O-mode polarized beams are coupled into the same transmission waveguide and launch antenna.
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Affiliation(s)
- L Zeng
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - C Sung
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - R Lantsov
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
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12
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Wang G, Rhodes TL, Crocker NA, Peebles WA, Barada K. First step toward a synthetic diagnostic for magnetic fluctuation measurements using cross-polarization scattering on DIII-D. Rev Sci Instrum 2018; 89:10H113. [PMID: 30399840 DOI: 10.1063/1.5036791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 06/15/2018] [Indexed: 06/08/2023]
Abstract
Cross-polarization scattering (CPS) provides localized magnetic fluctuation ( B ̃ ) measurements in fusion plasmas based on the process where B ̃ scatters electromagnetic radiation into the orthogonal polarization. The CPS system on DIII-D utilizes the probe beam of a Doppler backscattering (DBS) diagnostic combined with a cross-view CPS receiver system, which allows simultaneous density and B ̃ measurements with good spatial and wavenumber coverage. The interpretation of the signals is challenging due to the complex plasma propagation of the DBS probe beam and CPS receive beams. A synthetic diagnostic for CPS is therefore essential to interpret data and perform detailed validation tests of non-linear turbulence simulations. This work reports a first step toward a synthetic diagnostic for CPS utilizing GENRAY, a 3-D ray tracing code, to simulate the propagation of the probe and scattered rays. The local B ̃ wavenumber is calculated from the local O- and X-mode wavenumbers using the wave vector matching scattering condition. The CPS wavenumber values and spatial locations are determined by a complex consideration that includes the local density and B ̃ level, receive antenna pattern and orientation, scattering volume, wavenumber values detected at the various scattering centers, and alignment of the magnetic wave vector with the plane perpendicular to the magnetic field. The issue of a spurious CPS signal due to polarization mismatches for launch and receive is also discussed. It is suggested that simultaneous O- and X-mode DBS measurements should be utilized for better understanding of the CPS signal contamination when the cutoff locations for both polarizations are close.
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Affiliation(s)
- G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - N A Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - K Barada
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
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13
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Rhodes TL, Lantsov R, Wang G, Ellis R, Peebles WA. Optimized quasi-optical cross-polarization scattering system for the measurement of magnetic turbulence on the DIII-D tokamak. Rev Sci Instrum 2018; 89:10H107. [PMID: 30399735 DOI: 10.1063/1.5035427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Accepted: 06/04/2018] [Indexed: 06/08/2023]
Abstract
Simulations and laboratory tests are used to design and optimize a quasi-optical system for cross-polarization scattering (CPS) measurements of magnetic turbulence on the DIII-D tokamak. The CPS technique uses a process where magnetic turbulence scatters electromagnetic radiation into the perpendicular polarization enabling a local measurement of the perturbing magnetic fluctuations. This is a challenging measurement that addresses the contribution of magnetic turbulence to anomalous thermal transport in fusion research relevant plasmas. The goal of the new quasi-optical design is to demonstrate the full spatial and wavenumber capabilities of the CPS diagnostic. The approach used consists of independently controlled and in vacuo aiming systems for the probe and scattered beams (55-75 GHz).
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Affiliation(s)
- T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - R Lantsov
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - R Ellis
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
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14
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Barada K, Rhodes TL, Burrell KH, Zeng L, Bardóczi L, Chen X, Muscatello CM, Peebles WA. Quasistationary Plasma Predator-Prey System of Coupled Turbulence, Drive, and Sheared E×B Flow During High Performance DIII-D Tokamak Discharges. Phys Rev Lett 2018; 120:135002. [PMID: 29694164 DOI: 10.1103/physrevlett.120.135002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Indexed: 06/08/2023]
Abstract
A new, long-lived limit cycle oscillation (LCO) regime has been observed in the edge of near zero torque high performance DIII-D tokamak plasma discharges. These LCOs are localized and composed of density turbulence, gradient drives, and E×B velocity shear damping (E and B are the local radial electric and total magnetic fields). Density turbulence sequentially acts as a predator (via turbulence transport) of profile gradients and a prey (via shear suppression) to the E×B velocity shear. Reported here for the first time is a unique spatiotemporal variation of the local E×B velocity, which is found to be essential for the existence of this system. The LCO system is quasistationary, existing from 3 to 12 plasma energy confinement times (∼30-900 LCO cycles) limited by hardware constraints. This plasma system appears to contribute strongly to the edge transport in these high performance and transient-free plasmas, as evident from oscillations in transport relevant edge parameters at LCO time scale.
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Affiliation(s)
- K Barada
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - K H Burrell
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - L Zeng
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - L Bardóczi
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Xi Chen
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - C M Muscatello
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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15
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Wang G, Peebles WA, Doyle EJ, Crocker NA, Wannberg C, Lau C, Hanson GR, Doane JL. Evaluation of low-frequency operational limit of proposed ITER low-field-side reflectometer waveguide run including miter bends. Rev Sci Instrum 2017; 88:103508. [PMID: 29092526 DOI: 10.1063/1.4995662] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The present design concept for the ITER low-field-side reflectometer transmission line (TL) consists of an ∼40 m long, 6.35 cm diameter helically corrugated waveguide (WG) together with ten 90° miter bends. This paper presents an evaluation of the TL performance at low frequencies (33-50 GHz) where the predicted HE11 mode ohmic and mode conversion losses start to increase significantly. Quasi-optical techniques were used to form a near Gaussian beam to efficiently couple radiation in this frequency range into the WG. It was observed that the output beams from the guide remained linearly polarized with cross-polarization power levels of ∼1.5%-3%. The polarization rotation due to the helical corrugations was in the range ∼1°-3°. The radiated beam power profiles typically show excellent Gaussian propagation characteristics at distances >20 cm from the final exit aperture. The round trip propagation loss was found to be ∼2.5 dB at 50 GHz and ∼6.5 dB at 35 GHz, showing an inverse increase with frequency. This was consistent with updated calculations of miter bend and ohmic losses. At low frequencies (33-50 GHz), the mode purity remained very good at the exit of the waveguide, and the losses are perfectly acceptable for operation in ITER. The primary challenge may come from the future addition of a Gaussian telescope and other filter components within the corrugated guide, which will likely introduce additional perturbations to the beam profile and an increase in mode-conversion loss.
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Affiliation(s)
- G Wang
- Department of Physics and Astronomy and PSTI, UCLA, Los Angeles, California 90095, USA
| | - W A Peebles
- Department of Physics and Astronomy and PSTI, UCLA, Los Angeles, California 90095, USA
| | - E J Doyle
- Department of Physics and Astronomy and PSTI, UCLA, Los Angeles, California 90095, USA
| | - N A Crocker
- Department of Physics and Astronomy and PSTI, UCLA, Los Angeles, California 90095, USA
| | - C Wannberg
- Department of Physics and Astronomy and PSTI, UCLA, Los Angeles, California 90095, USA
| | - C Lau
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - G R Hanson
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - J L Doane
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
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16
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Hu JQ, Zhou C, Liu AD, Wang MY, Doyle EJ, Peebles WA, Wang G, Zhang XH, Zhang J, Feng X, Ji JX, Li H, Lan T, Xie JL, Ding WX, Liu WD, Yu CX. An eight-channel Doppler backscattering system in the experimental advanced superconducting tokamak. Rev Sci Instrum 2017; 88:073504. [PMID: 28764527 DOI: 10.1063/1.4991855] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Doppler backscattering system can measure the perpendicular velocity and fluctuation amplitude of the density turbulence with intermediate wavenumber. An eight-channel Doppler backscattering system has been installed in the Experimental Advanced Superconducting Tokamak (EAST), which can probe eight different radial locations simultaneously by launching eight fixed frequencies (55, 57.5, 60, 62.5, 67.5, 70, 72.5, 75 GHz) into plasma. The quasi-optical system consists of circular corrugated waveguide transmission, a fixed parabolic mirror, and a rotatable parabolic mirror which are integrated with quasi-optics front-end of the profile reflectometer inside the vacuum vessel. The incidence angle can be chosen from 5° to 12°, and the wavenumber range is 2-15/cm with the wavenumber resolution Δk/k≤0.21. Ray tracing simulations are used to calculate the scattering locations and the perpendicular wavenumber. The dynamic range of this new eight-channel Doppler backscattering system can be as large as 40 dB in the EAST. In this article, the hardware design, the ray tracing, and the preliminary experimental results in the EAST will be presented.
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Affiliation(s)
- J Q Hu
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - C Zhou
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - A D Liu
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - M Y Wang
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - E J Doyle
- Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095, USA
| | - G Wang
- Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095, USA
| | - X H Zhang
- School of Computer and Information, Hefei University of Technology, Hefei, Anhui 230026, China
| | - J Zhang
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - X Feng
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - J X Ji
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - H Li
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - T Lan
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - J L Xie
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - W X Ding
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - W D Liu
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
| | - C X Yu
- KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026, China
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17
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Kubota S, Majeski R, Peebles WA, Bell RE, Boyle DP, Kaita R, Kozub T, Lucia M, Merino E, Nguyen XV, Rhodes TL, Schmitt JC. A frequency-modulated continuous-wave reflectometer for the Lithium Tokamak Experiment. Rev Sci Instrum 2017; 88:053502. [PMID: 28571454 DOI: 10.1063/1.4981811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The frequency-modulated continuous-wave reflectometer on LTX (Lithium Tokamak Experiment) and the data analysis methods used for determining electron density profiles are described. The diagnostic uses a frequency range of 13.1-33.5 GHz, for covering a density range of 0.21-1.4×1013 cm-3 (in O-mode polarization) with a time resolution down to 8 μs. The design of the diagnostic incorporates the concept of an "optimized" source frequency sweep, which minimizes the large variation in the intermediate frequency signal due to a long dispersive transmission line. The quality of the raw data is dictated by the tuning characteristics of the microwave sources, as well as the group delay ripple in the transmission lines, which can generate higher-order nonlinearities in the frequency sweep. Both effects are evaluated for our diagnostic and best practices are presented for minimizing "artifacts" generated in the signals. The quality of the reconstructed profiles is also improved using two additional data analysis methods. First, the reflectometer data are processed as a radar image, where clutter due to echoes from the wall and backscattering from density fluctuations can be easily identified and removed. Second, a weighed least-squares lamination algorithm POLAN (POLynomial ANalysis) is used to reconstruct the electron density profile. Examples of density profiles in LTX are presented, along with comparisons to measurements from the Thomson scattering and the λ = 1 mm interferometer diagnostics.
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Affiliation(s)
- S Kubota
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - R Majeski
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - R E Bell
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - D P Boyle
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - R Kaita
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - T Kozub
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - M Lucia
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - E Merino
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - X V Nguyen
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - J C Schmitt
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
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18
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Rhodes TL, Barada K, Peebles WA, Crocker NA. Simultaneous measurement of magnetic and density fluctuations via cross-polarization scattering and Doppler backscattering on the DIII-D tokamak. Rev Sci Instrum 2016; 87:11E726. [PMID: 27910380 DOI: 10.1063/1.4960601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
An upgraded cross-polarization scattering (CPS) system for the simultaneous measurement of internal magnetic fluctuations B̃ and density fluctuations ñ is presented. The system has eight radial quadrature channels acquired simultaneously with an eight-channel Doppler backscattering system (measures density fluctuations ñ and flows). 3-D ray tracing calculations based on the GENRAY ray tracing code are used to illustrate the scattering and geometric considerations involved in the CPS implementation on DIII-D. A unique quasi-optical design and IF electronics system allow direct comparison of B̃ and ñ during dynamic or transient plasma events (e.g., Edge Localized Modes or ELMs, L to H-mode transitions, etc.). The system design allows the interesting possibility of both magnetic-density (B̃-ñ) fluctuation and magnetic-temperature (B̃-T̃) fluctuation cross-phase measurements suitable for detailed tests of turbulence simulations.
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Affiliation(s)
- T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - K Barada
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - N A Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
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19
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Wang G, Doyle EJ, Peebles WA. Front-end antenna system design for the ITER low-field-side reflectometer system using GENRAY ray tracing. Rev Sci Instrum 2016; 87:11E712. [PMID: 27910606 DOI: 10.1063/1.4960500] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A monostatic antenna array arrangement has been designed for the microwave front-end of the ITER low-field-side reflectometer (LFSR) system. This paper presents details of the antenna coupling coefficient analyses performed using GENRAY, a 3-D ray tracing code, to evaluate the plasma height accommodation capability of such an antenna array design. Utilizing modeled data for the plasma equilibrium and profiles for the ITER baseline and half-field scenarios, a design study was performed for measurement locations varying from the plasma edge to inside the top of the pedestal. A front-end antenna configuration is recommended for the ITER LFSR system based on the results of this coupling analysis.
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Affiliation(s)
- G Wang
- Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095, USA
| | - E J Doyle
- Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095, USA
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20
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Barada K, Rhodes TL, Crocker NA, Peebles WA. Measurement of local, internal magnetic fluctuations via cross-polarization scattering in the DIII-D tokamak (invited). Rev Sci Instrum 2016; 87:11E601. [PMID: 27910576 DOI: 10.1063/1.4960154] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We present new measurements of internal magnetic fluctuations obtained with a novel eight channel cross polarization scattering (CPS) system installed on the DIII-D tokamak. Measurements of internal, localized magnetic fluctuations provide a window on an important physics quantity that we heretofore have had little information on. Importantly, these measurements provide a new ability to challenge and test linear and nonlinear simulations and basic theory. The CPS method, based upon the scattering of an incident microwave beam into the opposite polarization by magnetic fluctuations, has been significantly extended and improved over the method as originally developed on the Tore Supra tokamak. A new scattering geometry, provided by a unique probe beam, is utilized to improve the spatial localization and wavenumber range. Remotely controllable polarizer and mirror angles allow polarization matching and wavenumber selection for a range of plasma conditions. The quasi-optical system design, its advantages and challenges, as well as important physics validation tests are presented and discussed. Effect of plasma beta (ratio of kinetic to magnetic pressure) on both density and magnetic fluctuations is studied and it is observed that internal magnetic fluctuations increase with beta. During certain quiescent high confinement operational regimes, coherent low frequency modes not detected by magnetic probes are detected locally by CPS diagnostics.
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Affiliation(s)
- K Barada
- University of California-Los Angeles, P.O. Box 957099, Los Angeles, California 90095, USA
| | - T L Rhodes
- University of California-Los Angeles, P.O. Box 957099, Los Angeles, California 90095, USA
| | - N A Crocker
- University of California-Los Angeles, P.O. Box 957099, Los Angeles, California 90095, USA
| | - W A Peebles
- University of California-Los Angeles, P.O. Box 957099, Los Angeles, California 90095, USA
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21
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Zeng L, Doyle EJ, Rhodes TL, Wang G, Sung C, Peebles WA, Bobrek M. A novel technique for real-time estimation of edge pedestal density gradients via reflectometer time delay data. Rev Sci Instrum 2016; 87:11E719. [PMID: 27910620 DOI: 10.1063/1.4961289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A new model-based technique for fast estimation of the pedestal electron density gradient has been developed. The technique uses ordinary mode polarization profile reflectometer time delay data and does not require direct profile inversion. Because of its simple data processing, the technique can be readily implemented via a Field-Programmable Gate Array, so as to provide a real-time density gradient estimate, suitable for use in plasma control systems such as envisioned for ITER, and possibly for DIII-D and Experimental Advanced Superconducting Tokamak. The method is based on a simple edge plasma model with a linear pedestal density gradient and low scrape-off-layer density. By measuring reflectometer time delays for three adjacent frequencies, the pedestal density gradient can be estimated analytically via the new approach. Using existing DIII-D profile reflectometer data, the estimated density gradients obtained from the new technique are found to be in good agreement with the actual density gradients for a number of dynamic DIII-D plasma conditions.
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Affiliation(s)
- L Zeng
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - E J Doyle
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - C Sung
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - M Bobrek
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6006, USA
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22
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Sung C, Peebles WA, Wannberg C, Rhodes TL, Nguyen X, Lantsov R, Bardóczi L. A frequency tunable, eight-channel correlation ECE system for electron temperature turbulence measurements on the DIII-D tokamak. Rev Sci Instrum 2016; 87:11E123. [PMID: 27910687 DOI: 10.1063/1.4961296] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A new eight-channel correlation electron cyclotron emission diagnostic has recently been installed on the DIII-D tokamak to study both turbulent and coherent electron temperature fluctuations under various plasma conditions and locations. This unique system is designed to cover a broad range of operation space on DIII-D (1.6-2.1 T, detection frequency: 72-108 GHz) via four remotely selected local oscillators (80, 88, 96, and 104 GHz). Eight radial locations are measured simultaneously in a single discharge covering as much as half the minor radius. In this paper, we present design details of the quasi-optical system, the receiver, as well as representative data illustrating operation of the system.
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Affiliation(s)
- C Sung
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - C Wannberg
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - X Nguyen
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - R Lantsov
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
| | - L Bardóczi
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA
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23
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Bardóczi L, Rhodes TL, Carter TA, Bañón Navarro A, Peebles WA, Jenko F, McKee G. Modulation of Core Turbulent Density Fluctuations by Large-Scale Neoclassical Tearing Mode Islands in the DIII-D Tokamak. Phys Rev Lett 2016; 116:215001. [PMID: 27284662 DOI: 10.1103/physrevlett.116.215001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Indexed: 06/06/2023]
Abstract
We report the first observation of localized modulation of turbulent density fluctuations n[over ˜] (via beam emission spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment n[over ˜] was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that n[over ˜] could be dominantly driven by the ion temperature gradient instability.
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Affiliation(s)
- L Bardóczi
- University of California Los Angeles, Los Angeles, California 90095, USA
| | - T L Rhodes
- University of California Los Angeles, Los Angeles, California 90095, USA
| | - T A Carter
- University of California Los Angeles, Los Angeles, California 90095, USA
| | - A Bañón Navarro
- University of California Los Angeles, Los Angeles, California 90095, USA
| | - W A Peebles
- University of California Los Angeles, Los Angeles, California 90095, USA
| | - F Jenko
- University of California Los Angeles, Los Angeles, California 90095, USA
| | - G McKee
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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24
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Zeng L, Peebles WA, Doyle EJ, Rhodes TL, Crocker N, Nguyen X, Wannberg CW, Wang G. Performance and data analysis aspects of the new DIII-D monostatic profile reflectometer system. Rev Sci Instrum 2014; 85:11D843. [PMID: 25430256 DOI: 10.1063/1.4889775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A new frequency-modulated profile reflectometer system, featuring a monostatic antenna geometry (using one microwave antenna for both launch and receive), has been installed on the DIII-D tokamak, providing a first experimental test of this measurement approach for profile reflectometry. Significant features of the new system are briefly described in this paper, including the new monostatic arrangement, use of overmoded, broadband transmission waveguide, and dual-polarization combination/demultiplexing. Updated data processing and analysis, and in-service performance aspects of the new monostatic profile reflectometer system are also presented. By using a raytracing code (GENRAY) to determine the approximate trajectory of the probe beam, the electron density (ne) profile can be successfully reconstructed with L-mode plasmas vertically shifted by more than 10 cm off the vessel midplane. Specifically, it is demonstrated that the new system has a capability to measure ne profiles with plasma vertical offsets of up to ±17 cm. Examples are also presented of accurate, high time and spatial resolution density profile measurements made over a wide range of DIII-D conditions, e.g., the measured temporal evolution of the density profile across a L-H transition.
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Affiliation(s)
- L Zeng
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - E J Doyle
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - N Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - X Nguyen
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - C W Wannberg
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
| | - G Wang
- Physics and Astronomy Department, University of California, Los Angeles, California 90095, USA
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25
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Rhodes TL, Peebles WA, Crocker NA, Nguyen X. Development of a cross-polarization scattering system for the measurement of internal magnetic fluctuations in the DIII-D tokamak. Rev Sci Instrum 2014; 85:11D838. [PMID: 25430251 DOI: 10.1063/1.4887276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The design and performance of a new cross-polarization scattering (CPS) system for the localized measurement of internal magnetic fluctuations is presented. CPS is a process whereby magnetic fluctuations scatter incident electromagnetic radiation into a perpendicular polarization which is subsequently detected. A new CPS design that incorporates a unique scattering geometry was laboratory tested, optimized, and installed on the DIII-D tokamak. Plasma tests of signal-to-noise, polarization purity, and frequency response indicate proper functioning of the system. CPS data show interesting features related to internal MHD perturbations known as sawteeth that are not observed on density fluctuations.
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Affiliation(s)
- T L Rhodes
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - N A Crocker
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
| | - X Nguyen
- Physics and Astronomy Department, University of California, Los Angeles, California 90098, USA
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Schmitz L, Ruskov E, Deng BH, Gota H, Gupta D, Tuszewski M, Douglass J, Peebles WA, Binderbauer M, Tajima T. Multi-channel Doppler backscattering measurements in the C-2 field reversed configuration. Rev Sci Instrum 2014; 85:11D840. [PMID: 25430253 DOI: 10.1063/1.4891415] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A versatile heterodyne Doppler Backscattering (DBS) system is used to measure density fluctuation levels (in the wavenumber range kρs ≤ 50), and the toroidal E × B flow velocity in the C-2 Field-Reversed Configuration (FRC). Six tunable frequencies in three waveguide bands (26 GHz ≤ f ≤ 90 GHz) are launched using monostatic beam optics, via a quasi-optical beam combiner/polarizer and an adjustable parabolic focusing mirror (inside the vacuum enclosure) achieving Gaussian beam spot sizes of 3-5.5 cm at the X/O-mode cutoff. The DBS system covers plasma densities of 0.8 × 10(13) ≤ ne ≤ 1 × 10(14) cm(-3), and provides access to the FRC core (up to the field null) and across the FRC separatrix into the scrape-off layer plasma.
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Affiliation(s)
- L Schmitz
- Department of Physics & Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - E Ruskov
- Department of Physics & Astronomy, University of California, Irvine, Irvine, California 92697, USA
| | - B H Deng
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
| | - H Gota
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
| | - D Gupta
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
| | - M Tuszewski
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
| | - J Douglass
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
| | - W A Peebles
- Department of Physics & Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - M Binderbauer
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
| | - T Tajima
- Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688, USA
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Hillesheim JC, DeBoo JC, Peebles WA, Carter TA, Wang G, Rhodes TL, Schmitz L, McKee GR, Yan Z, Staebler GM, Burrell KH, Doyle EJ, Holland C, Petty CC, Smith SP, White AE, Zeng L. Observation of a critical gradient threshold for electron temperature fluctuations in the DIII-D Tokamak. Phys Rev Lett 2013; 110:045003. [PMID: 25166172 DOI: 10.1103/physrevlett.110.045003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Indexed: 06/03/2023]
Abstract
A critical gradient threshold has been observed for the first time in a systematic, controlled experiment for a locally measured turbulent quantity in the core of a confined high-temperature plasma. In an experiment in the DIII-D tokamak where L(T(e))(-1) = |∇T(e)|/T(e) and toroidal rotation were varied, long wavelength (k(θ)ρ(s) ≲ 0.4) electron temperature fluctuations exhibit a threshold in L(T(e))(-1): below, they change little; above, they steadily increase. The increase in δT(e)/T(e) is concurrent with increased electron heat flux and transport stiffness. Observations were insensitive to rotation. Accumulated evidence strongly enforces the identification of the experimentally observed threshold with ∇T(e)-driven trapped electron mode turbulence.
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Affiliation(s)
- J C Hillesheim
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - J C DeBoo
- General Atomics, San Diego, California 92186-5608, USA
| | - W A Peebles
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - T A Carter
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - G Wang
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - T L Rhodes
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - L Schmitz
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - G R McKee
- University of Wisconsin Madison, Madison, Wisconsin 53706-1687, USA
| | - Z Yan
- University of Wisconsin Madison, Madison, Wisconsin 53706-1687, USA
| | - G M Staebler
- General Atomics, San Diego, California 92186-5608, USA
| | - K H Burrell
- General Atomics, San Diego, California 92186-5608, USA
| | - E J Doyle
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
| | - C Holland
- University of California at San Diego, La Jolla, California 92093-0417, USA
| | - C C Petty
- General Atomics, San Diego, California 92186-5608, USA
| | - S P Smith
- General Atomics, San Diego, California 92186-5608, USA
| | - A E White
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - L Zeng
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90024-1547, USA
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Sung C, White AE, Irby JH, Leccacorvi R, Vieira R, Oi CY, Peebles WA, Nguyen X. Design of a correlation electron cyclotron emission diagnostic for Alcator C-Mod. Rev Sci Instrum 2012; 83:10E311. [PMID: 23126971 DOI: 10.1063/1.4731750] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A correlation electron cyclotron emission (CECE) diagnostic has been installed in Alcator C-Mod. In order to measure electron temperature fluctuations, this diagnostic uses a spectral decorrelation technique. Constraints obtained with nonlinear gyrokinetic simulations guided the design of the optical system and receiver. The CECE diagnostic is designed to measure temperature fluctuations which have k(θ) ≤ 4.8 cm(-1) (k(θ)ρ(s) < 0.5) using a well-focused beam pattern. Because the CECE diagnostic is a dedicated turbulence diagnostic, the optical system is also flexible, which allows for various collimating lenses and antenna to be used. The system overview and the demonstration of its operability as designed are presented in this paper.
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Affiliation(s)
- C Sung
- Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139, USA.
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29
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Zhang J, Peebles WA, Carter TA, Crocker NA, Doyle EJ, Kubota S, Nguyen X, Rhodes TL, Wannberg C, Zeng L. Design of a millimeter-wave polarimeter for NSTX-Upgrade and initial test on DIII-D. Rev Sci Instrum 2012; 83:10E321. [PMID: 23126979 DOI: 10.1063/1.4733735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Polarimetry is a powerful diagnostic technique to probe plasma equilibria and magnetic fluctuations in fusion plasmas. In a high beta plasma such as the National Spherical Torus eXperiment (NSTX), these measurements are important to understand plasma stability and anomalous transport. A 288 GHz polarimeter operating along a major radial chord in retroreflection geometry has been developed and is being tested on the DIII-D tokamak to prepare for future implementation on NSTX-Upgrade. The system launches a rotating linearly polarized beam and detects the phase shift directly related to the polarization change caused by the plasma. To accomplish this, a pair of orthogonal linearly polarized beams with a stable difference frequency is generated using a single sideband modulation technique, then combined and transformed to be counter-rotating circularly polarized. To improve phase resolution, quasi-optical isolation, using Faraday rotators and polarizers, is utilized to eliminate a multi-path feedback effect, which is found to be the primary source of phase error. The bench tests in the laboratory and DIII-D power supply test discharges indicate ≤1° phase resolution.
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Affiliation(s)
- J Zhang
- Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547, USA.
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30
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Schmitz L, Zeng L, Rhodes TL, Hillesheim JC, Doyle EJ, Groebner RJ, Peebles WA, Burrell KH, Wang G. Role of zonal flow predator-prey oscillations in triggering the transition to H-mode confinement. Phys Rev Lett 2012; 108:155002. [PMID: 22587261 DOI: 10.1103/physrevlett.108.155002] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Indexed: 05/31/2023]
Abstract
Direct evidence of zonal flow (ZF) predator-prey oscillations and the synergistic roles of ZF- and equilibrium E×B flow shear in triggering the low- to high-confinement (L- to H-mode) transition in the DIII-D tokamak is presented. Periodic turbulence suppression is first observed in a narrow layer at and just inside the separatrix when the shearing rate transiently exceeds the turbulence decorrelation rate. The final transition to H mode with sustained turbulence and transport reduction is controlled by equilibrium E×B shear due to the increasing ion pressure gradient.
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Affiliation(s)
- L Schmitz
- University of California-Los Angeles, Los Angeles, California 90095, USA
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31
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Hillesheim JC, Peebles WA, Rhodes TL, Schmitz L, White AE, Carter TA. New plasma measurements with a multichannel millimeter-wave fluctuation diagnostic system in the DIII-D tokamak (invited). Rev Sci Instrum 2010; 81:10D907. [PMID: 21033939 DOI: 10.1063/1.3466900] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A novel multichannel, tunable Doppler backscattering (DBS)/reflectometry system has recently been developed and applied to a variety of DIII-D plasmas. Either DBS or reflectometry can be easily configured for use in a wide range of plasma conditions using a flexible quasi-optical antenna system. The multiple closely spaced channels, when combined with other fluctuation diagnostic systems, have opened up new measurements of plasma properties. For example, the toroidal and fine-scale radial structure of coherent plasma oscillations, such as geodesic acoustic modes, have been probed simultaneously in the core of high temperature plasmas by applying correlation analysis between two toroidally separated DBS systems, as well as within the multichannel array. When configured as a reflectometer, cross-correlation with electron cyclotron emission radiometry has uncovered detailed information regarding the crossphase relationship between density and temperature fluctuations. The density-temperature crossphase measurement yields insight into the physics of tokamak turbulence at a fundamental level that can be directly compared with predictions from nonlinear gyrokinetic simulations.
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Affiliation(s)
- J C Hillesheim
- Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095-1547, USA.
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32
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Peebles WA, Rhodes TL, Hillesheim JC, Zeng L, Wannberg C. A novel, multichannel, comb-frequency Doppler backscatter system. Rev Sci Instrum 2010; 81:10D902. [PMID: 21033934 DOI: 10.1063/1.3464266] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Doppler backscattering has emerged in recent years as a powerful diagnostic tool in high temperature fusion plasmas. The technique is sensitive to plasma turbulence flow and has been utilized to determine radial electric field and to study geodesic acoustic modes, zonal flows, and intermediate scale density turbulence. The current manuscript describes a novel technique for creating a stable, multichannel system covering the V-band frequency range (50-75 GHz) which enables simultaneous monitoring of turbulent flows and fluctuation levels at eight distinct spatial locations. The system is based on a high-frequency, low phase noise comb-frequency generator combined with a filter bank and quadrature detection system. The system is now in operation on DIII-D and has allowed monitoring of the flow and turbulence levels across the plasma radius during events such as the L-H transition.
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Affiliation(s)
- W A Peebles
- University of California, Los Angeles, California 90095, USA.
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33
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Zhang J, Crocker NA, Carter TA, Kubota S, Peebles WA. Interaction between Faraday rotation and Cotton-Mouton effects in polarimetry modeling for NSTX. Rev Sci Instrum 2010; 81:10D519. [PMID: 21033874 DOI: 10.1063/1.3479042] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The evolution of electromagnetic wave polarization is modeled for propagation in the major radial direction in the National Spherical Torus Experiment with retroreflection from the center stack of the vacuum vessel. This modeling illustrates that the Cotton-Mouton effect-elliptization due to the magnetic field perpendicular to the propagation direction-is shown to be strongly weighted to the high-field region of the plasma. An interaction between the Faraday rotation and Cotton-Mouton effects is also clearly identified. Elliptization occurs when the wave polarization direction is neither parallel nor perpendicular to the local transverse magnetic field. Since Faraday rotation modifies the polarization direction during propagation, it must also affect the resultant elliptization. The Cotton-Mouton effect also intrinsically results in rotation of the polarization direction, but this effect is less significant in the plasma conditions modeled. The interaction increases at longer wavelength and complicates interpretation of polarimetry measurements.
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Affiliation(s)
- J Zhang
- Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547, USA.
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34
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Rhodes TL, Peebles WA, Nguyen X, Hillesheim JC, Schmitz L, White AE, Wang G. Quasioptical design of integrated Doppler backscattering and correlation electron cyclotron emission systems on the DIII-D tokamak. Rev Sci Instrum 2010; 81:10D912. [PMID: 21033944 DOI: 10.1063/1.3475797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The quasioptical design of a new integrated Doppler backscattering (DBS) and correlation electron cyclotron emission (CECE) system is presented. The design provides for simultaneous measurements of intermediate wavenumber density and long wavelength electron temperature turbulence behavior. The Doppler backscattering technique is sensitive to plasma turbulence flow and has been utilized to determine radial electric field, geodesic acoustic modes, zonal flows, and intermediate scale (k∼1-6 cm(-1)) density turbulence. The correlation ECE system measures a second turbulent field, electron temperature fluctuations, and is sensitive to long poloidal wavelength (k≤1.8 cm(-1)). The integrated system utilizes a newly installed in-vessel focusing mirror that produces a beam waist diameter of 3.5-5 cm in the plasma depending on the frequency. A single antenna (i.e., monostatic operation) is used for both launch and receive. The DBS wavenumber is selected via an adjustable launch angle and variable probing frequency. Due to the unique system design both positive and negative wavenumbers can be obtained, with a range of low to intermediate wavenumbers possible (approximately -3 to 10 cm(-1)). A unique feature of the design is the ability to place the DBS and CECE measurements at the same radial and poloidal locations allowing for cross correlation studies (e.g., measurement of nT cross-phase).
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Affiliation(s)
- T L Rhodes
- Department of Physics and Astronomy, University of California, Los Angeles, California 90098, USA.
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35
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Wang G, Rhodes TL, Peebles WA, Harvey RW, Budny RV. Refractive and relativistic effects on ITER low field side reflectometer design. Rev Sci Instrum 2010; 81:10D908. [PMID: 21033940 DOI: 10.1063/1.3478632] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The ITER low field side reflectometer faces some unique design challenges, among which are included the effect of relativistic electron temperatures and refraction of probing waves. This paper utilizes GENRAY, a 3D ray tracing code, to investigate these effects. Using a simulated ITER operating scenario, characteristics of the reflected millimeter waves after return to the launch plane are quantified as a function of a range of design parameters, including antenna height, antenna diameter, and antenna radial position. Results for edge/SOL measurement with both O- and X-mode polarizations using proposed antennas are reported.
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Affiliation(s)
- G Wang
- University of California, Los Angeles, California 90095, USA.
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36
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Kubota S, Peebles WA, Nguyen XV, Crocker NA, Roquemore AL, Holoman T, Guttadora L, Kaita R. A Ka-band tunable direct-conversion correlation reflectometer for NSTX. Rev Sci Instrum 2010; 81:10D917. [PMID: 21033949 DOI: 10.1063/1.3490024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The recent availability of broadband microwave quadrature mixers in the Ka-band (28-40 GHz) of frequencies has allowed the fabrication of low-cost direct-conversion detection circuits for use in the variable-frequency correlation reflectometer on the National Spherical Torus eXperiment (NSTX). The quadrature receiver in this case can be implemented as a simple homodyne circuit, without the complication of a single-sideband modulator or a feedforward tracking circuit present in more typical designs. A pair of direct-conversion receivers is coupled with broadband microwave voltage-controlled oscillators to construct a flexible dual-channel radar system with a fast frequency settling time of ∼160 μs. A detailed description of the design and a full characterization of the hardware are provided. Examples of turbulence measurements from radial and poloidal correlation reflectometry on NSTX using a poloidal array of antennas (oriented normal to the magnetic flux surfaces for conventional reflectometry) are presented.
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Affiliation(s)
- S Kubota
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA.
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37
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Hillesheim JC, Peebles WA, Rhodes TL, Schmitz L, Carter TA, Gourdain PA, Wang G. A multichannel, frequency-modulated, tunable Doppler backscattering and reflectometry system. Rev Sci Instrum 2009; 80:083507. [PMID: 19725655 DOI: 10.1063/1.3205449] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A novel multichannel Doppler backscattering system has been designed and tested for application on the DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] and National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] fusion plasma devices. Doppler backscattering measures localized intermediate wavenumber (k(perpendicular)rho(i) approximately 1-4,k(perpendicular) approximately 2-15 cm(-1)) density fluctuations and the propagation velocity of turbulent structures. Microwave radiation is launched at a frequency that approaches a cutoff layer in the plasma and at an angle that is oblique to the cutoff layer. Bragg backscattering occurs near the cutoff layer for fluctuations with k(perpendicular) approximately -2k(i), where k(i) is the incident probe wave vector at the scattering location. The turbulence propagation velocity can be determined from the Doppler shift in the return signal together with knowledge of the scattering wavenumber. Ray tracing simulations are used to determine k(perpendicular) and the scattering location. Frequency modulation of a voltage-controlled solid state microwave source followed by frequency multiplication is used to create an array of finely spaced (Delta f=350 MHz) frequencies spanning 1.4 GHz. The center of the array bandwidth is tunable within the range of approximately 53-78 GHz. This article details the system design, laboratory tests, and presents initial data from DIII-D plasmas.
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Affiliation(s)
- J C Hillesheim
- Department of Physics and Astronomy, University of California-Los Angeles, Los Angeles, California 90095-1547, USA.
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38
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Gourdain PA, Peebles WA. Application of reflectometry power flow for magnetic field pitch angle measurements in tokamak plasmas (invited). Rev Sci Instrum 2008; 79:10F102. [PMID: 19044589 DOI: 10.1063/1.2969075] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Reflectometry has successfully demonstrated measurements of many important parameters in high temperature tokamak fusion plasmas. However, implementing such capabilities in a high-field, large plasma, such as ITER, will be a significant challenge. In ITER, the ratio of plasma size (meters) to the required reflectometry source wavelength (millimeters) is significantly larger than in existing fusion experiments. This suggests that the flow of the launched reflectometer millimeter-wave power can be realistically analyzed using three-dimensional ray tracing techniques. The analytical and numerical studies presented will highlight the fact that the group velocity (or power flow) of the launched microwaves is dependent on the direction of wave propagation relative to the internal magnetic field. It is shown that this dependence strongly modifies power flow near the cutoff layer in a manner that embeds the local magnetic field direction in the "footprint" of the power returned toward the launch antenna. It will be shown that this can potentially be utilized to locally determine the magnetic field pitch angle at the cutoff location. The resultant beam drift and distortion due to magnetic field and relativistic effects also have significant consequences on the design of reflectometry systems for large, high-field fusion experiments. These effects are discussed in the context of the upcoming ITER burning plasma experiment.
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Affiliation(s)
- P-A Gourdain
- Department of Physics and Astronomy, University of California Los Angeles, California 90095-1547, USA.
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39
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White AE, Schmitz L, Peebles WA, Carter TA, Rhodes TL, Doyle EJ, Gourdain PA, Hillesheim JC, Wang G, Holland C, Tynan GR, Austin ME, McKee GR, Shafer MW, Burrell KH, Candy J, DeBoo JC, Prater R, Staebler GM, Waltz RE, Makowski MA. A correlation electron cyclotron emission diagnostic and the importance of multifield fluctuation measurements for testing nonlinear gyrokinetic turbulence simulations. Rev Sci Instrum 2008; 79:103505. [PMID: 19044712 DOI: 10.1063/1.2981186] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A correlation electron cyclotron emission (CECE) diagnostic has been used to measure local, turbulent fluctuations of the electron temperature in the core of DIII-D plasmas. This paper describes the hardware and testing of the CECE diagnostic and highlights the importance of measurements of multifield fluctuation profiles for the testing and validation of nonlinear gyrokinetic codes. The process of testing and validating such codes is critical for extrapolation to next-step fusion devices. For the first time, the radial profiles of electron temperature and density fluctuations are compared to nonlinear gyrokinetic simulations. The CECE diagnostic at DIII-D uses correlation radiometry to measure the rms amplitude and spectrum of the electron temperature fluctuations. Gaussian optics are used to produce a poloidal spot size with w(o) approximately 1.75 cm in the plasma. The intermediate frequency filters and the natural linewidth of the EC emission determine the radial resolution of the CECE diagnostic, which can be less than 1 cm. Wavenumbers resolved by the CECE diagnostic are k(theta) < or = 1.8 cm(-1) and k(r) < or = 4 cm(-1), relevant for studies of long-wavelength turbulence associated with the trapped electron mode and the ion temperature gradient mode. In neutral beam heated L-mode plasmas, core electron temperature fluctuations in the region 0.5 < r/a < 0.9, increase with radius from approximately 0.5% to approximately 2%, similar to density fluctuations that are measured simultaneously with beam emission spectroscopy. After incorporating "synthetic diagnostics" to effectively filter the code output, the simulations reproduce the characteristics of the turbulence and transport at one radial location r/a = 0.5, but not at a second location, r/a = 0.75. These results illustrate that measurements of the profiles of multiple fluctuating fields can provide a significant constraint on the turbulence models employed by the code.
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Affiliation(s)
- A E White
- University of California-Los Angeles, Los Angeles, California 90095, USA
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40
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Schmitz L, Wang G, Hillesheim JC, Rhodes TL, Peebles WA, White AE, Zeng L, Carter TA, Solomon W. Detection of zonal flow spectra in DIII-D by a dual-channel Doppler backscattering system. Rev Sci Instrum 2008; 79:10F113. [PMID: 19044597 DOI: 10.1063/1.2953675] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Doppler backscattering (DBS) has been successfully used to measure the E x B flow velocity and local intermediate wavenumber density fluctuation levels in the DIII-D tokamak. Depending on the launch angle and the frequency of the probing beam, the signal backscattered from the plasma cut-off layer is sensitive to density fluctuations at a specific perpendicular wavenumber (1 < or = k(perpendicular rho(s)) < or = 4). Due to the localization and high time resolution for poloidal flow measurements, DBS is well suited to detect stationary and time-dependent shear flows [zonal flows (ZFs)]. We present a novel scheme to measure ZF spectra using a dual-channel DBS system capable of simultaneously probing two minor radii separated by a distance of 0.2 cm < Delta r < 3 cm. Frequency spectra of geodesic acoustic modes and low frequency ZFs (f or = 10 kHz) have been obtained for 0.6 < r/a < 0.95.
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Affiliation(s)
- L Schmitz
- UCLA Physics and Astronomy Department, Los Angeles, California 90095-1547, USA
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41
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Schmitz L, White AE, Carter TA, Peebles WA, Rhodes TL, Burrell KH, Solomon W, Staebler GM. Observation of reduced electron-temperature fluctuations in the core of H-mode plasmas. Phys Rev Lett 2008; 100:035002. [PMID: 18232989 DOI: 10.1103/physrevlett.100.035002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Indexed: 05/25/2023]
Abstract
Core electron-temperature fluctuations [0.5%< or =T[over ]_(e)/T_(e)< or =2%, k_(theta)rho_(s)< or =0.3 in neutral-beam-heated low confinement-mode (L-mode) plasmas] are observed to decrease by at least a factor of 4 in standard and quiescent high-confinement-mode (H-mode and QH-mode) regimes in the DIII-D tokamak (r/a=0.7). These fluctuations are attributed to ion temperature gradient (ITG) modes stabilized by rotational shear at the H-mode transition. The simultaneous reduction in electron heat diffusivity (chi_(e)(QH)/chi_(e)(L)<0.25) suggests that T[over ]_(e) fluctuations can contribute significantly to L-mode electron heat transport.
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Affiliation(s)
- L Schmitz
- Department of Physics and Astronomy, University of California-Los Angeles, Los Angeles, CA 90024-2704, USA
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Crocker NA, Peebles WA, Kubota S, Fredrickson ED, Kaye SM, LeBlanc BP, Menard JE. Three-wave interactions between fast-ion modes in the National Spherical Torus Experiment. Phys Rev Lett 2006; 97:045002. [PMID: 16907581 DOI: 10.1103/physrevlett.97.045002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Indexed: 05/11/2023]
Abstract
Simultaneous bursts of energetic particle mode (EPM) and toroidicity-induced Alfvén eigenmode (TAE) activity that correlate with significant fast-ion loss are observed in beam heated plasmas. Three-wave interactions between these modes are conclusively identified, indicating fixed phase relationships. This nonlinear coupling concentrates the energy of the TAEs into a toroidally localized perturbation frozen in the frame of a rigid, toroidally rotating structure formed by the EPMs. This redistribution of energy is significant because it will modify the effect of the TAEs on fast-ion loss.
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Affiliation(s)
- N A Crocker
- University of California, Los Angeles, California 90095-7099, USA
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Nazikian R, Berk HL, Budny RV, Burrell KH, Doyle EJ, Fonck RJ, Gorelenkov NN, Holcomb C, Kramer GJ, Jayakumar RJ, La Haye RJ, McKee GR, Makowski MA, Peebles WA, Rhodes TL, Solomon WM, Strait EJ, Vanzeeland MA, Zeng L. Multitude of core-localized shear Alfvén waves in a high-temperature fusion plasma. Phys Rev Lett 2006; 96:105006. [PMID: 16605746 DOI: 10.1103/physrevlett.96.105006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2005] [Indexed: 05/08/2023]
Abstract
Evidence is presented for a multitude of discrete frequency Alfvén waves in the core of magnetically confined high-temperature fusion plasmas. Multiple diagnostic instruments confirm wave excitation over a wide spatial range from the device size at the longest wavelengths down to the thermal ion Larmor radius. At the shortest scales, the poloidal wavelengths are comparable to the scale length of electrostatic drift wave turbulence. Theoretical analysis confirms a dominant interaction of the modes with particles in the thermal ion distribution traveling well below the Alfvén velocity.
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Affiliation(s)
- R Nazikian
- Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543, USA.
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Schmidt JA, Thomassen KI, Goldston RJ, Neilson GH, Nevins WM, Sinnis JC, Andersen P, Bair W, Barr WL, Batchelor DB, Baxi C, Berg G, Bernabei S, Bialek JM, Bonoli PT, Boozer A, Bowers D, Bronner G, Brooks JN, Brown TG, Bulmer R, Butner D, Campbell R, Casper T, Chaniotakis E, Chaplin M, Chen SJ, Chin E, Chrzanowski J, Citrolo J, Cole MJ, Dahlgren F, Davis FC, Davis J, Davis S, Diatchenko N, Dinkevich S, Feldshteyn Y, Felker B, Feng T, Fenstermacher ME, Fleming R, Fogarty PJ, Fragetta W, Fredd E, Gabler M, Galambos J, Gohar Y, Goranson PL, Greenough N, Grisham LR, Haines J, Haney S, Hassenzahl W, Heim J, Heitzenroeder PJ, Hill DN, Hodapp T, Houlberg WA, Hubbard A, Hyatt A, Jackson M, Jaeger EF, Jardin SC, Johnson J, Jones GH, Juliano DR, Junge R, Kalish M, Kessel CE, Knutson D, LaHaye RJ, Lang DD, Langley RA, Liew SL, Lu E, Mantz H, Manickam J, Mau TK, Medley S, Mikkelsen DR, Miller R, Monticello D, Morgan D, Moroz P, Motloch C, Mueller J, Myatt L, Nelson BE, Neumeyer CL, Nilson D, O'Conner T, Pearlstein LD, Peebles WA, Pelovitz M, Perkins FW, Perkins LJ, Petersen D, Pillsbury R, Politzer PA, Pomphrey N, Porkolab M, Posey A, Radovinsky A, Raftopoulis S, Ramakrishnan S, Ramos J, Rauch W, Ravenscroft D, Redler K, Reiersen WT, Reiman A, Reis E, Rewoldt G, Richards DJ, Rocco R, Rognlien TD, Ruzic D, Sabbagh S, Sapp J, Sayer RO, Scharer JE, Schmitz L, Schnitz J, Sevier L, Shipley SE, Simmons RT, Slack D, Smith GR, Stambaugh R, Steill G, Stevenson T, Stoenescu S, Onge KTS, Stotler DP, Strait T, Strickler DJ, Swain DW, Tang W, Tuszewski M, Ulrickson MA, VonHalle A, Walker MS, Wang C, Wang P, Warren J, Werley KA, West WP, Williams F, Wong R, Wright K, Wurden GA, Yugo JJ, Zakharov L, Zbasnik J. The design of the Tokamak Physics Experiment (TPX). J Fusion Energ 1993. [DOI: 10.1007/bf01079667] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Rettig CL, Peebles WA, Burrell KH, La Haye RJ, Doyle EJ, Groebner RJ, Luhmann NC. Microturbulence damping mechanisms in the DIII‐D tokamak*. ACTA ACUST UNITED AC 1993. [DOI: 10.1063/1.860727] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Philipona R, Doyle EJ, Luhmann NC, Peebles WA, Rettig CL, Groebner RJ, Burrell KH, Gohil P, Matsumoto H, Stambaugh RD. Two‐stage turbulence suppression and E×B velocity shear measured at the L–H transition. ACTA ACUST UNITED AC 1993. [DOI: 10.1063/1.860871] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Bravenec RV, Gentle KW, Richards B, Ross DW, Sing DC, Wootton AJ, Brower DL, Luhmann NC, Peebles WA, Yu CX, Crowley TP, Heard JW, Hickok RL, Schoch PM, Yang XZ. Core turbulence and transport studies on the Texas Experimental Tokamak. ACTA ACUST UNITED AC 1992. [DOI: 10.1063/1.860019] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Brower DL, Yu CX, Bravenec RV, Lin H, Luhmann NC, Peebles WA, Ritz CP, Smith BA, Wootton AJ, Zhang ZM, Zhao SJ. Brower et al. reply. Phys Rev Lett 1992; 68:892. [PMID: 10046020 DOI: 10.1103/physrevlett.68.892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Ross DW, Bravenec RV, Ritz CP, Sloan ML, Thompson JR, Wootton AJ, Schoch PM, Heard JW, Crowley TP, Hickok RL, Simcic V, Brower DL, Peebles WA, Luhmann NC. Comparison of drift wave models with fluctuation data from the interior of the TEXT tokamak. ACTA ACUST UNITED AC 1991. [DOI: 10.1063/1.859644] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Doyle EJ, Groebner RJ, Burrell KH, Gohil P, Lehecka T, Luhmann NC, Matsumoto H, Osborne TH, Peebles WA, Philipona R. Modifications in turbulence and edge electric fields at the L–H transition in the DIII‐D tokamak. ACTA ACUST UNITED AC 1991. [DOI: 10.1063/1.859597] [Citation(s) in RCA: 215] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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