High count rate pulse height analysis spectroscopy on the TCV tokamak

A liquid nitrogen cooled solid state Ge diode has been installed on the TCV tokamak to examine the X-ray spectrum from ≅1→100 kev. The electronics for signal processing and data acquisition have been optimised to improve the data throughput to match the high flux 2 sec time duration of a TCV plasma pulse. The plasma electron temperature has been measured both in L and H-mode type discharges and the observed count rate and spectral shape varied using externally selectable apertures and Be filters. No linear radiation from intrinsic impurities has been observed in either case. The effect of pulse pile-up in such a system is analysed both experimentally and using a numerical model. The maximum count rate is shown to be limited by the analogue electronics processing but not by the signal processing. (author) 9 figs., tabs., 9 refs