Spatially resolved spectra from a new x-ray imaging crystal spectrometer for measurements of ion and electron temperature profiles (invited)

Abstract

A new type of high-resolution x-ray imaging crystal spectrometer is being developed to measure ion and electron temperature profiles in tokamak plasmas. The instrument is particularly valuable for diagnosing plasmas with purely ohmic heating and rf heating, since it does not require the injection of a neutral beam-although it can also be used for the diagnosis of neutral-beam heated plasmas. The spectrometer consists of a spherically bent quartz crystal and a two-dimensional position-sensitive detector. It records spectra of helium-like argon (or krypton) from multiple sightlines through the plasma and projects a de-magnified image of a large plasma cross section onto the detector. The spatial resolution in the plasma is solely determined by the height of the crystal, its radius of curvature, and the Bragg angle. This new x-ray imaging crystal spectrometer may also be of interest for the diagnosis of ion temperature profiles in future large tokamaks, the Korea Superconducting Tokamak Advanced Research tokamak and the International Thermonuclear Experimental Reactor, where the application of the presently used charge-exchange spectroscopy will be difficult, if the neutral beams do not penetrate to the plasma center. The article presents the results from proof-of-principle experiments performed with a prototype instrument at Alcator C-Mod.

Spectral resolution measurement of an x-ray imaging crystal spectrometer for KSTAR

“…The engineering design, fabrication details, and research and development for the XICS were discussed in previous papers. [2][3][4][5] The XICS for the KSTAR device is based on an advanced imaging spectrometer, 6 which utilizes the astigmatism of a spherical mirror. The XICS will provide measurements of the profiles of the ion and electron temperatures, toroidal rotation velocity, impurity charge-state distributions, and ionization equilibrium from the heliumlike argon ͑Ar XVII͒ spectra.…”

Application of PILATUS II Detector Modules for High Resolution X-Ray Imaging Crystal Spectrometers on the Alcator C-Mod Tokamak

“…With this experimental arrangement one obtains only limited information (five points) on the radial profiles of these important plasma parameters, which is not sufficient for detailed comparisons with predictions from modern transport codes. It is, therefore, planned to replace the von Hamos spectrometers by a X-ray imaging crystal spectrometer with a spherically bent crystal and a two-dimensional, positionsensitive detector [1] that would record spectra with a much higher throughput and spatial resolution. However, the lack of appropriate detectors has delayed a realization of this project until now, since the requirements, namely, a single-photon count rate capability of > 500 kHz per mm 2 , a spatial resolution of < 0.2 mm, a high detection efficiency for X-ray energies of 3.1 keV, and a large detector area of at least 35 mm x 240 mm, are very challenging.…”

“…The proof of principle of the imaging spectrometer was demonstrated on Alcator C-Mod in 2003, using a multi-wire proportional counter [1]. However, the global count rate capability of this detector of 400 kHz has limited the time resolution of the spectrometer to > 100 ms.…”

Passive Spectroscopic Diagnostics for Magnetically-confined Fusion Plasmas

“…[282][283][284][285] The instrument consists of a spherically bent crystal and a two-dimensional detector, which are arranged in a Johann configuration. The imaging properties of this configuration have been discussed by Bitter et al 252 and Bertschinger et al…”