Digital processing of solid state detector signals in pellet charge exchange measurements on LHD.

Radially resolved measurements of the plasma ion distribution function by detecting charge exchange neutrals from an impurity pellet ablation cloud require a fast operating energy analyzer working at high count rates to build several spectra during the pellet flight. Currently a solid state detector in the pulse height analysis (PHA) mode is used for such measurements on the Large Helical Device. Traditional PHA techniques cannot provide the operating speed required for a good spatial resolution. An algorithm has been proposed based on digital processing of noisy data series containing charge-sensitive preamplifier signals with discontinuities corresponding to incident particles. The algorithm employs the modified Tikhonov regularization and the successive detection–estimation of signal increments at discontinuity points. Such an approach allows one to realize an ultrafast particle energy spectroscopy by taking advantage of detector/preamplifier capabilities without limiting the system throughput by subsequent electronics. [ABSTRACT FROM AUTHOR]