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Varennes R, Garbet X, Vermare L, Sarazin Y, Dif-Pradalier G, Grandgirard V, Ghendrih P, Donnel P, Peret M, Obrejan K, Bourne E. Synergy of Turbulent Momentum Drive and Magnetic Braking. PHYSICAL REVIEW LETTERS 2022; 128:255002. [PMID: 35802431 DOI: 10.1103/physrevlett.128.255002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 02/17/2022] [Accepted: 06/10/2022] [Indexed: 06/15/2023]
Abstract
In absence of external torque, plasma rotation in tokamaks results from a balance between collisional magnetic braking and turbulent drive. The outcome of this competition and cooperation is essential to determine the plasma flow. A reduced model, supported by gyrokinetic simulations, is first used to explain and quantify the competition only. The ripple amplitude above which magnetic drag overcomes turbulent viscosity is obtained. The synergetic impact of ripple on the turbulent toroidal Reynolds stress is explored. Simulations show that the main effect comes from an enhancement of the radial electric field shear by the ripple, which in turn impacts the residual stress.
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Affiliation(s)
- R Varennes
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | - X Garbet
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | - L Vermare
- LPP, CNRS, Ecole polytechnique, 91128 Palaiseau, France
| | - Y Sarazin
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | | | | | - P Ghendrih
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | - P Donnel
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | - M Peret
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | - K Obrejan
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
| | - E Bourne
- CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France
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2
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Terry PW, Li PY, Pueschel MJ, Whelan GG. Threshold Heat-Flux Reduction by Near-Resonant Energy Transfer. PHYSICAL REVIEW LETTERS 2021; 126:025004. [PMID: 33512223 DOI: 10.1103/physrevlett.126.025004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Revised: 12/22/2020] [Accepted: 01/04/2021] [Indexed: 06/12/2023]
Abstract
Near-resonant energy transfer to large-scale stable modes is shown to reduce transport above the linear critical gradient, contributing to the onset of transport at higher gradients. This is demonstrated for a threshold fluid theory of ion temperature gradient turbulence based on zonal-flow-catalyzed transfer. The heat flux is suppressed above the critical gradient by resonance in the triplet correlation time, a condition enforced by the wave numbers of the interaction of the unstable mode, zonal flow, and stable mode.
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Affiliation(s)
- P W Terry
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - P-Y Li
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - M J Pueschel
- Dutch Institute for Fundamental Energy Research, 5612 AJ Eindhoven, Netherlands
- Eindhoven University of Technology, 5600 MB Eindhoven, Netherlands
- Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712, USA
| | - G G Whelan
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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3
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Isotope effects in self-organization of internal transport barrier and concomitant edge confinement degradation in steady-state LHD plasmas. Sci Rep 2019; 9:15913. [PMID: 31685863 PMCID: PMC6828710 DOI: 10.1038/s41598-019-52271-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Accepted: 10/15/2019] [Indexed: 12/04/2022] Open
Abstract
The isotope effect, which has been a long-standing mystery in the turbulent magnetically confined plasmas, is the phenomena that the plasma generated with heavier hydrogen isotope show a mitigated transport. This is on the contrary to what is predicted with the simple scaling theory, in which the heavier ions easily diffuse because of its larger gyro-radius. Thanks to the newly developed analysis method and a comprehensive parameter scan experiment in the steady-state plasmas in the Large Helical Device (LHD), the isotope effect was clearly observed in the self-organized internal transport barrier (ITB) structure for the first time. Comparing the ITB intensity in deuterium (D) and hydrogen (H) plasmas, two distinct hydrogen isotope effects are found: stronger ITB is formed in D plasmas and a significant edge confinement degradation accompanied by the ITB formation emerges in H plasmas. This observation sheds light on a new aspect of the turbulent plasmas regarding how the basic properties of the fluid material affect the turbulent structure formation in the open-system.
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4
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Ishizawa A, Urano D, Nakamura Y, Maeyama S, Watanabe TH. Persistence of Ion Temperature Gradient Turbulent Transport at Finite Normalized Pressure. PHYSICAL REVIEW LETTERS 2019; 123:025003. [PMID: 31386508 DOI: 10.1103/physrevlett.123.025003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 05/17/2019] [Indexed: 06/10/2023]
Abstract
Plasma β dependence of electromagnetic turbulent transport is investigated by means of gyrokinetic simulations with self-consistent change of the equilibrium magnetic field. It is found that energy transport due to ion-temperature-gradient (ITG) driven turbulence does not decrease with increasing β; that is, the ion energy diffusivity does not decrease, and the electron energy diffusivity increases with β. This is because magnetic fluctuations are significantly influenced by the background magnetic field structure change with β by the Pfirsch-Schluter current. The magnetic field change weakens the suppression effect of magnetic perturbations on the growth of the ITG mode, and it also suppresses nonlinear zonal flow production. The influence of the magnetic field change is significant as the global magnetic shear increases.
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Affiliation(s)
- A Ishizawa
- Graduate School of Energy Science, Kyoto University, Uji 611-0011, Japan
| | - D Urano
- Graduate School of Energy Science, Kyoto University, Uji 611-0011, Japan
| | - Y Nakamura
- Graduate School of Energy Science, Kyoto University, Uji 611-0011, Japan
| | - S Maeyama
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
| | - T-H Watanabe
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
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5
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Vaezi P, Holland C. An Improved Approach to Uncertainty Quantification for Plasma Turbulence Validation Studies. FUSION SCIENCE AND TECHNOLOGY 2018. [DOI: 10.1080/15361055.2017.1372987] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Payam Vaezi
- University of California San Diego, Center for Energy Research, 9500 Gilman Drive, La Jolla, California 92093
| | - Christopher Holland
- University of California San Diego, Center for Energy Research, 9500 Gilman Drive, La Jolla, California 92093
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6
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Houshmandyar S, Yang ZJ, Phillips PE, Rowan WL, Hubbard AE, Rice JE, Hughes JW, Wolfe SM. Temperature gradient scale length measurement: A high accuracy application of electron cyclotron emission without calibration. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:11E101. [PMID: 27910677 DOI: 10.1063/1.4955297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Calibration is a crucial procedure in electron temperature (Te) inference from a typical electron cyclotron emission (ECE) diagnostic on tokamaks. Although the calibration provides an important multiplying factor for an individual ECE channel, the parameter ΔTe/Te is independent of any calibration. Since an ECE channel measures the cyclotron emission for a particular flux surface, a non-perturbing change in toroidal magnetic field changes the view of that channel. Hence the calibration-free parameter is a measure of Te gradient. BT-jog technique is presented here which employs the parameter and the raw ECE signals for direct measurement of electron temperature gradient scale length.
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Affiliation(s)
- S Houshmandyar
- Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Z J Yang
- Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - P E Phillips
- Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712, USA
| | - W L Rowan
- Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712, USA
| | - A E Hubbard
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02129, USA
| | - J E Rice
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02129, USA
| | - J W Hughes
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02129, USA
| | - S M Wolfe
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02129, USA
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7
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Zhong WL, Shen Y, Zou XL, Gao JM, Shi ZB, Dong JQ, Duan XR, Xu M, Cui ZY, Li YG, Ji XQ, Yu DL, Cheng J, Xiao GL, Jiang M, Yang ZC, Zhang BY, Shi PW, Liu ZT, Song XM, Ding XT, Liu Y. Observation of Double Impurity Critical Gradients for Electromagnetic Turbulence Excitation in Tokamak Plasmas. PHYSICAL REVIEW LETTERS 2016; 117:045001. [PMID: 27494476 DOI: 10.1103/physrevlett.117.045001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Indexed: 06/06/2023]
Abstract
The impact of impurity ions on a pedestal has been investigated in the HL-2A Tokamak, at the Southwestern Institute of Physics, Chengdu, China. Experimental results have clearly shown that during the H-mode phase, an electromagnetic turbulence was excited in the edge plasma region, where the impurity ions exhibited a peaked profile. It has been found that double impurity critical gradients are responsible for triggering the turbulence. Strong stiffness of the impurity profile has been observed during cyclic transitions between the I-phase and H-mode regime. The results suggest that the underlying physics of the self-regulated edge impurity profile offers the possibility for an active control of the pedestal dynamics via pedestal turbulence.
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Affiliation(s)
- W L Zhong
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Y Shen
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - X L Zou
- CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France
| | - J M Gao
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Z B Shi
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - J Q Dong
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
- Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, People's Republic of China
| | - X R Duan
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - M Xu
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Z Y Cui
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Y G Li
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - X Q Ji
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - D L Yu
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - J Cheng
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - G L Xiao
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - M Jiang
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Z C Yang
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - B Y Zhang
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - P W Shi
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Z T Liu
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - X M Song
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - X T Ding
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
| | - Yong Liu
- Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People's Republic of China
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8
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Xanthopoulos P, Mynick HE, Helander P, Turkin Y, Plunk GG, Jenko F, Görler T, Told D, Bird T, Proll JHE. Controlling turbulence in present and future stellarators. PHYSICAL REVIEW LETTERS 2014; 113:155001. [PMID: 25375712 DOI: 10.1103/physrevlett.113.155001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Indexed: 06/04/2023]
Abstract
Turbulence is widely expected to limit the confinement and, thus, the overall performance of modern neoclassically optimized stellarators. We employ novel petaflop-scale gyrokinetic simulations to predict the distribution of turbulence fluctuations and the related transport scaling on entire stellarator magnetic surfaces and reveal striking differences to tokamaks. Using a stochastic global-search optimization method, we derive the first turbulence-optimized stellarator configuration stemming from an existing quasiomnigenous design.
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Affiliation(s)
- P Xanthopoulos
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - H E Mynick
- Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA
| | - P Helander
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - Y Turkin
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - G G Plunk
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - F Jenko
- Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany
| | - T Görler
- Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany
| | - D Told
- Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany
| | - T Bird
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
| | - J H E Proll
- Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
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9
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Citrin J, Jenko F, Mantica P, Told D, Bourdelle C, Garcia J, Haverkort JW, Hogeweij GMD, Johnson T, Pueschel MJ. Nonlinear stabilization of tokamak microturbulence by fast ions. PHYSICAL REVIEW LETTERS 2013; 111:155001. [PMID: 24160605 DOI: 10.1103/physrevlett.111.155001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Indexed: 06/02/2023]
Abstract
Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regimes is shown to be a key factor in reducing tokamak microturbulence, augmenting significantly the thermal pressure electromagnetic stabilization. Based on nonlinear gyrokinetic simulations investigating a set of ion heat transport experiments on the JET tokamak, described by Mantica et al. [Phys. Rev. Lett. 107, 135004 (2011)], this result explains the experimentally observed ion heat flux and stiffness reduction. These findings are expected to improve the extrapolation of advanced tokamak scenarios to reactor relevant regimes.
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Affiliation(s)
- J Citrin
- FOM Institute DIFFER-Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, PO Box 1207, 3430 BE Nieuwegein, The Netherlands and CEA, IRFM, F-13108 Saint Paul Lez Durance, France
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10
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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. PHYSICAL REVIEW LETTERS 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] [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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11
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Parra FI, Nave MFF, Schekochihin AA, Giroud C, de Grassie JS, Severo JHF, de Vries P, Zastrow KD. Scaling of spontaneous rotation with temperature and plasma current in tokamaks. PHYSICAL REVIEW LETTERS 2012; 108:095001. [PMID: 22463645 DOI: 10.1103/physrevlett.108.095001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Indexed: 05/31/2023]
Abstract
Using theoretical arguments, a simple scaling law for the size of the intrinsic rotation observed in tokamaks in the absence of a momentum injection is found: The velocity generated in the core of a tokamak must be proportional to the ion temperature difference in the core divided by the plasma current, independent of the size of the device. The constant of proportionality is of the order of 10 km·s(-1)·MA·keV(-1). When the intrinsic rotation profile is hollow, i.e., it is countercurrent in the core of the tokamak and cocurrent in the edge, the scaling law presented in this Letter fits the data remarkably well for several tokamaks of vastly different size and heated by different mechanisms.
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Affiliation(s)
- F I Parra
- Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, UK.
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12
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Mantica P, Angioni C, Challis C, Colyer G, Frassinetti L, Hawkes N, Johnson T, Tsalas M, deVries PC, Weiland J, Baiocchi B, Beurskens MNA, Figueiredo ACA, Giroud C, Hobirk J, Joffrin E, Lerche E, Naulin V, Peeters AG, Salmi A, Sozzi C, Strintzi D, Staebler G, Tala T, Van Eester D, Versloot T. A key to improved ion core confinement in the JET tokamak: ion stiffness mitigation due to combined plasma rotation and low magnetic shear. PHYSICAL REVIEW LETTERS 2011; 107:135004. [PMID: 22026864 DOI: 10.1103/physrevlett.107.135004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Indexed: 05/31/2023]
Abstract
New transport experiments on JET indicate that ion stiffness mitigation in the core of a rotating plasma, as described by Mantica et al. [Phys. Rev. Lett. 102, 175002 (2009)] results from the combined effect of high rotational shear and low magnetic shear. The observations have important implications for the understanding of improved ion core confinement in advanced tokamak scenarios. Simulations using quasilinear fluid and gyrofluid models show features of stiffness mitigation, while nonlinear gyrokinetic simulations do not. The JET experiments indicate that advanced tokamak scenarios in future devices will require sufficient rotational shear and the capability of q profile manipulation.
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Affiliation(s)
- P Mantica
- Istituto di Fisica del Plasma "P. Caldirola," Associazione Euratom-ENEA-CNR, Milano, Italy
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13
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Barnes M, Parra FI, Highcock EG, Schekochihin AA, Cowley SC, Roach CM. Turbulent transport in tokamak plasmas with rotational shear. PHYSICAL REVIEW LETTERS 2011; 106:175004. [PMID: 21635042 DOI: 10.1103/physrevlett.106.175004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Indexed: 05/30/2023]
Abstract
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal E×B shear value for plasma confinement. Local maxima in the momentum fluxes are observed, implying the possibility of bifurcations in the E×B shear. The critical temperature gradient for the onset of turbulence increases with flow shear at low flow shears; at higher flow shears, the dependence of heat flux on temperature gradient becomes less stiff. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity.
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Affiliation(s)
- M Barnes
- Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, United Kingdom.
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14
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Highcock EG, Barnes M, Schekochihin AA, Parra FI, Roach CM, Cowley SC. Transport bifurcation in a rotating tokamak plasma. PHYSICAL REVIEW LETTERS 2010; 105:215003. [PMID: 21231311 DOI: 10.1103/physrevlett.105.215003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Indexed: 05/30/2023]
Abstract
The effect of flow shear on turbulent transport in tokamaks is studied numerically in the experimentally relevant limit of zero magnetic shear. It is found that the plasma is linearly stable for all nonzero flow shear values, but that subcritical turbulence can be sustained nonlinearly at a wide range of temperature gradients. Flow shear increases the nonlinear temperature gradient threshold for turbulence but also increases the sensitivity of the heat flux to changes in the temperature gradient, except over a small range near the threshold where the sensitivity is decreased. A bifurcation in the equilibrium gradients is found: for a given input of heat, it is possible, by varying the applied torque, to trigger a transition to significantly higher temperature and flow gradients.
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Affiliation(s)
- E G Highcock
- Rudolph Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford, OX1 3NP, United Kingdom.
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15
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Nave MFF, Johnson T, Eriksson LG, Crombé K, Giroud C, Mayoral ML, Ongena J, Salmi A, Tala T, Tsalas M. Influence of magnetic field ripple on the intrinsic rotation of tokamak plasmas. PHYSICAL REVIEW LETTERS 2010; 105:105005. [PMID: 20867528 DOI: 10.1103/physrevlett.105.105005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2010] [Indexed: 05/29/2023]
Abstract
Using the unique capability of JET to monotonically change the amplitude of the magnetic field ripple, without modifying other relevant equilibrium conditions, the effect of the ripple on the angular rotation frequency of the plasma column was investigated under the conditions of no external momentum input. The ripple amplitude was varied from 0.08% to 1.5% in Ohmic and ion-cyclotron radio-frequency (ICRF) heated plasmas. In both cases the ripple causes counterrotation, indicating a strong torque due to nonambipolar transport of thermal ions and in the case of ICRF also fast ions.
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Affiliation(s)
- M F F Nave
- Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear-Laboratorio Associado, Lisbon, Portugal
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