Tomography of the fast electron bremsstrahlung emission during lower hybrid current drive on TORE SUPRA

A new tomography dedicated to detailed studies of the fast electron bremsst rahlung emission in the hard x-ray (HXR) energy range between 20 and 200 ke V during lower hybrid (LH) current drive experiments on the TORE SUPRA toka mak [Equipe TORE SUPRA, in Proceedings of the 15th Conference on Plasma Phy sics and Controlled Nuclear Fusion Research, Seville (International Atomic Energy Agency, Vienna, 1995), Vol. 1, AIEA-CN-60 /A1-5, p. 105] is presente d. Radiation detection is performed by cadmium telluride semiconductors, wh ich have most of the desirable features for a powerful diagnosing of magnet ically confined hot plasmas-compact size, high x-ray stopping efficiency, f ast timing characteristics, good energy resolution, no sensitivity to magne tic field, reasonable susceptibility to performance degradation from neutro n/gamma-induced damages. This instrument is made of two independent cameras viewing a poloidal cross-section of the plasma, with respectively 21 and 3 8 detectors. A coarse spectrometry-8 energy channels-is carried out for eac h chord, with an energy resolution of 20 keV. The spatial resolution in the core of the plasma is 4-5 cm, while the time sampling may be lowered down to of 2-4 ms. Powerful inversion techniques based on maximum entropy or reg ularization algorithms take full advantage of the large number of line-inte grated measurements for very robust estimates of the local HXR profiles as a function of time and photon energy. A detailed account of main characteri stics and performances of the diagnostic is reported, as well as preliminar y results on LH current drive experiments. (C) 1999 American Institute of P hysics. [S0034-6748(99)03210-4].