Recent upgrades to MST'’s soft-x-ray spectroscopy diagnostic

In MST RFP plasmas, electron energization during tearing mode reconnection events was recently observed via soft-x-ray (sxr) emission [1]. X-ray measurements from 3-25 keV during these short-lived ($<$ 100 $\mu$s) events were achieved with a detector consisting of an avalanche photodiode and a 20 ns Gaussian shaping amplifier (GSA) whose output was digitized at 500 MHz [2]. A radially resolved measurement of x-ray emission from 2-10 keV can also be made with an existing array of six Amptek XR-100CR sxr detectors, each comprised of a Si photodiode, a charge-sensitive preamplifier, a thermoelectric cooler, and a Cremat GSA CR-200-500ns having a pulse FWHM of about 1200 ns [3]. One upgrade to this system entails a CR-200-25ns GSA which will reduce the FWHM to 60 ns. The digitization rate is also increased from 60 MHz to 240 MHz, sufficient to resolve a 60 ns Gaussian pulse. The upgrade will also incorporate improved shielding from IGBT switching noise arising from MST’s Bt and Bp programmable power supplies. Housing the detector assembly within Compac-SRF-series enclosures attenuates noise at 20 MHz by 80 dB. Initial measurements will be presented. [1] A.M.DuBois,et al.,PRL submitted [2] A.M.DuBois, et al.,RSI,86,073512(2015) [3] D.J.Clayton,et al., RSI,81,10E308(2010)