Development and energy calibration of Si-FNA for LHD fast ion measurement

Abstract

A Si-FNA (silicon-diode-based fast neutral analyzer) was newly developed at NIFS, which uses an electrically cooled silicon-diode as an energy analyzer. Si-FNA is suitable for energy-resolved profile measurements of fast neutrals since it is compact and inexpensive. Two Si-FNAs were recently designed and installed on the Large Helical Device (LHD) during the experimental campaign of 1999. The basic performance of a Si-FNA was examined by using x/γ-ray sources of ${}^{57}\mathrm{Co}$ and ${}^{241}\mathrm{Am}.$ An energy resolution of about 3.5 keV was achieved for optimum shaping times and a resolution of about 6 keV was achieved for shorter shaping times which allowed for the higher counting rates required for LHD. The energy calibration for fast neutrals was performed by injecting neutral beams (NB) into the LHD vessel without target plasmas present. An energy loss of about 37 keV and an energy broadening of about 4.5 keV were observed at the calibration. Excellent slowing-down energy spectra are obtained for NB-injected fast particles without any influences of x/γ-rays.