Suprathermal electron studies in the TCV tokamak: Design of a tomographic hard-x-ray spectrometer

Abstract

Electron cyclotron resonance heating and electron cyclotron current drive, disruptive events, and sawtooth activity are all known to produce suprathermal electrons in fusion devices, motivating increasingly detailed studies of the generation and dynamics of this suprathermal population. Measurements have been performed in the past years in the tokamak à configuration variable ͑TCV͒ tokamak using a single pinhole hard-x-ray ͑HXR͒ camera and electron-cyclotron-emission radiometers, leading, in particular, to the identification of the crucial role of spatial transport in the physics of ECCD. The observation of a poloidal asymmetry in the emitted suprathermal bremsstrahlung radiation motivates the design of a proposed new tomographic HXR spectrometer reported in this paper. The design, which is based on a compact modified Soller collimator concept, is being aided by simulations of tomographic reconstruction. Quantitative criteria have been developed to optimize the design for the greatly variable shapes and positions of TCV plasmas.

Tomographic analysis of the nonthermal x-ray bursts during disruption instability in the T-10 tokamak

“…14 The tomographic reconstruction technique based on CdTe detectors was realized previously in two-camera systems built in TORE SUPRA 15 and TCV. 11,12 The work performed on TORE SUPRA 15 was concerned with analysis of the nonthermal electrons during experiments with application of the Low-Hybrid waves (see also experiments with tangential hard x-ray imaging in PBX-M 16 ), while evolution of the fast electrons during a disruption instability was not analyzed in details. Essential new results of the present experiments in T-10 tokamak is evaluation of spatial and temporal evolution of the localized nonthermal electrons (E γ ∼ 15-150 keV) during initial stage of the disruption instability.…”

“…In order to increase sensitivity to the non-thermal radiation (with simultaneous retention of the high temporal resolution) the cadmium telluride (CdTe) detectors are used in modern experiments. 2, [8][9][10][11][12][13] The cadmium based detectors are characterized by high photon absorption efficiency due to the high atomic number (Z = 48/52) and high density (6 g/cm 3 ) and high resistivity because of the wide band gap (1.4 eV at 300 K). 14 The tomographic reconstruction technique based on CdTe detectors was realized previously in two-camera systems built in TORE SUPRA 15 and TCV.…”

Hard X-Ray Tomographic Spectroscopy In Tcv

“…A tomographic system is then necessary to resolve the full 2D poloidal distribution. Such a system has now been developed for TCV, comprising three cameras (with a fourth one planned), and utilizing state-of-the-art technology and methods [5,6,7,8]. This constitutes the first system of its kind applied to a noncircular tokamak plasma.…”

The science program of the TCV tokamak: exploring fusion reactor and power plant concepts

“…A tomographic hard X-ray spectrometer (HXRS) has been developed [24] to study the dynamics of suprathermal electrons through their bremsstrahlung emission and has recently generated first results from three of the eventual four cameras. Using advanced digital pulse recognition techniques [25], the first tomographic inversions of HXR data from a shaped tokamak plasma have now been produced.…”