Low-noise, high-speed detector development for optical turbulence fluctuation measurements for NSTX.

TLDR: A new beam emission spectroscopy (BES) diagnostic is under development that includes a next-generation preamplifier and upgraded optical coupling system and notable features of the design are surface-mount components, minimized stray capacitance, a wide angular acceptance photodiode, a differential output line driver, and reduced input capacitance.

Abstract: A new beam emission spectroscopy (BES) diagnostic is under development Photon-noise limited measurements of neutral beam emissions are achieved using photoconductive photodiodes with a novel frequency-compensated broadband preamplifier The new BES system includes a next-generation preamplifier and upgraded optical coupling system Notable features of the design are surface-mount components, minimized stray capacitance, a wide angular acceptance photodiode, a differential output line driver, reduced input capacitance, doubling of the frequency range, net reduced electronic noise, and elimination of the need for a cryogenic cooling system The irreducible photon noise dominates the noise up to 800 kHz for a typical input power of 60 nW This new assembly is being integrated into an upgraded multichannel optical detector assembly for a new BES system on the NSTX experiment