Tangential x-ray imaging crystal spectrometer on J-TEXT tokamak

Observations of visible argon line emissions and its spatial profile from Aditya-U tokamak plasma

The spectroscopic studies of medium and high Z impurities have been the subject of interest in fusion research due to their role in mitigating plasma disruption and reducing heat load on the plasma facing components. Line emissions from these impurities provide the rotation velocity and ion temperature measurements along with the understanding of the overall impurity behavior in plasma. In the Aditya-U tokamak, the spatially resolved Ar II line emissions have been observed using a high resolution multi-track spectroscopic diagnostic consisting of a 1 m Czerny-Turner spectrometer coupled with a charge coupled device (CCD) detector using seven lines of sight viewing plasma tangentially along the toroidal direction. The spatially resolved Ar II lines at 458.96 nm have been observed. The singly ionized Ar emission peaks at the radial location of ρ = 0.8 of the plasma having a minor radius of 25 cm. Moreover, a 0.5 m UV-visible spectrometer coupled with a CCD detector and having a line of sight passing through the plasma midplane from the radial port was used to record visible Ar survey spectra within the 670-810 nm wavelength range, and all these lines have been identified for further analysis.

Design of tangential x-ray crystal spectrometer for Aditya-U tokamak

A tangential soft x-ray crystal spectrometer has been designed to measure the x-ray spectrum of He-like argon for the Aditya-U tokamak plasma. The system enables to measure electron temperature using the intensity ratio of the resonance line to the satellite line. For this purpose, an x-ray spectral line at 3.9494 Å from He-like argon, Ar¹⁶⁺, is considered. The spectrometer consists of a cylindrically bent silicon (111) crystal and a CCD detector to measure the resonance spectral line and its satellite lines in the wavelength region of 3.94-4.0 Å, viewing the plasma tangentially at an angle of 26° with respect to the toroidal direction in the magnetic axis. Considering Aditya-U tokamak plasma parameters and its geometrical constraints, plasma to crystal and crystal to detector distances have been kept at 1.47 m and 0.5 m, respectively, to detect a sufficient signal. The engineering design has been optimized after adequately addressing the issues related to port geometry and machine accessibility. Details on the design of the crystal spectrometer are presented in this paper.

Upgrades of poloidal and tangential x-ray imaging crystal spectrometers for temperature and rotation measurements on EAST

During the past two years, key parts of poloidal and tangential x-ray imaging crystal spectrometers (PXCSs and TXCSs) have been upgraded. For poloidal XCSs, double-crystals of ArXVII and FeXXV were deployed. For fulfilling in situ alignment of a poloidal XCS, the beryllium window must be flexibly removed. By utilizing a design, where the beryllium window was installed in the vacuum chamber of the double-crystal, and between the double-crystal and wall of this chamber, an in situ alignment for the two spectrometers was fulfilled. Also, a new holder for the double-crystal was installed to allow for precise adjustments of azimuth angle and vertical height of the double-crystal. In order to facilitate these adjustments of double-crystal and installation of beryllium window, the chamber of the double-crystal for PXCS was upgraded from a cylinder to a cuboid. The distance between double-crystal and magnetic axis was extended from 8936 mm to 9850 mm in order to improve spatial resolution for PXCS, which is currently in the range from 1.237 mm to 4.80 mm at magnetic axis. Furthermore, a new pixelated detector (PILATUS 900K), which has a large sensitive area of 83.8 × 325.3 mm² and which is vacuum compatible, is being implemented on the PXCS. This detector is mounted on a rail, so that its position can be changed by 50 mm to effectively record spectra of He-like argon and He-like iron (ArXVII and FeXXV). Similarly, a rail, which allows detector movement by 50 mm, was also installed in TXCS to alternatively record spectra of ArXVII and ArXVIII. Presently, the operation duration of PXCS and TXCS has been upgraded to hundreds of seconds in one shot. T_i- and u_ϕ-profiles measured by TXCS and charge exchange recombination spectroscopy (CXRS) were compared and found to be in good agreement.

Measurement of the electron and ion temperatures by the x-ray imaging crystal spectrometer on joint Texas experimental tokamak

An x-ray imaging crystal spectrometer has been developed on joint Texas experimental tokamak for the measurement of electron and ion temperatures from the K_α spectra of helium-like argon and its satellite lines. A two-dimensional multi-wire proportional counter has been applied to detect the spectra. The electron and ion temperatures have been obtained from the Voigt fitting with the spectra of helium-like argon ions. The profiles of electron and ion temperatures show the dependence on electron density in ohmic plasmas.

Wavelength calibration of x-ray imaging crystal spectrometer on Joint Texas Experimental Tokamak

The wavelength calibration of x-ray imaging crystal spectrometer is a key issue for the measurements of plasma rotation. For the lack of available standard radiation source near 3.95 Å and there is no other diagnostics to measure the core rotation for inter-calibration, an indirect method by using tokamak plasma itself has been applied on joint Texas experimental tokamak. It is found that the core toroidal rotation velocity is not zero during locked mode phase. This is consistent with the observation of small oscillations on soft x-ray signals and electron cyclotron emission during locked-mode phase.

Edge impurity rotation profile measurement by using high-resolution ultraviolet/visible spectrometer on J-TEXT

An upgrade of the edge rotation diagnostic system is achieved by increasing the number of viewing channels to 17 on J-TEXT tokamak. With the upgrade, the spatial resolution reaches 1 cm. The bulk plasma is used as the calibration light source. And the toroidal velocity profile of C V (carbon V) at edge region is obtained by using a spatial deconvolution technique. The valid measurement region is at ρ = 0.6-0.9, corresponding to the emitting region of C V. The preliminary experimental results express that the velocity of plasma may have a zero point near ρ = 0.85.

Upgraded high time-resolved x-ray imaging crystal spectroscopy system for J-TEXT ohmic plasmas

This paper presents the upgraded x-ray imaging crystal spectrometer (XICS) system on Joint Texas Experimental Tokamak (J-TEXT) tokamak and the latest experimental results obtained in last campaign. With 500 Hz frame rate of the new Pilatus detector and 5 cm × 10 cm spherically bent crystal, the XICS system can provide core electron temperature (Te), core ion temperature (Ti), and plasma toroidal rotation (VΦ) with a maximum temporal resolution of 2 ms for J-TEXT pure ohmic plasmas. These parameters with high temporal resolution are very useful in tokamak plasma research, especially for rapidly changed physical processes. The experimental results from the upgraded XICS system are presented.

Measurement of the edge plasma rotation on J-TEXT tokamak

A multi-channel high resolution spectrometer was developed for the measurement of the edge plasma rotation on J-TEXT tokamak. With the design of two opposite viewing directions, the poloidal and toroidal rotations can be measured simultaneously, and velocity accuracy is up to 1 km∕s. The photon flux was enhanced by utilizing combined optical fiber. With this design, the time resolution reaches 3 ms. An assistant software "Spectra Assist" was developed for implementing the spectrometer control and data analysis automatically. A multi-channel monochromatic analyzer is designed to get the location of chosen ions simultaneously through the inversion analysis. Some preliminary experimental results about influence of plasma density, different magnetohydrodynamics behaviors, and applying of biased electrode are presented.