Suprathermal electron studies in the TCV tokamak: design of a tomographic hard-X-ray spectrometer

Electron cyclotron resonance heating (ECRH) and current drive (ECCD), 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 past years in the TCV tokamak using a single pinhole hard-X-ray (HXR) camera and electron-cyclotron-emission (ECE) 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 poster. 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.