An application of electrically cooled Si detector to fast neutral measurement on CHS

Abstract

A new type of fast neutral particle analyzer using Si diode cooled by Peltier module has been designed and developed. It is known that leak current in a solid-state detector is reduced by its use in low temperature. It is shown in this article that Peltier effect provides a very handy way of cooling the detector as long as a temperature around 0 °C is aimed at. The detector was easily cooled down to −1.6 °C and the performance of the detector was studied by the use of x/γ rays from ${}^{\mathrm{241}}\mathrm{Am}.$ The leak current was remarkably reduced as the detector is cooled improving energy resolution from 9.2 keV at room temperature to 4.3 keV at −1.6 °C. In addition, the lower detectable energy limit was expanded from 25 keV to 14 keV. A Si detector is also sensitive to visible light and x ray. Therefore, the detector of our “reference design” is furnished with an evaporated 1000-Å-thick aluminum layer to reduce the visible light and with a lead collimator to reduce the x ray. The detector was finally installed on the Compact Helical System device for a test of overall performance and an energy spectrum from a diagnostic neutral beam was successfully measured. This test was conducted without an Al layer and this result suggests a possibility of eliminating it.