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

Schoenbeck, N. L.
Ellington, S. D.
Fonck, R. J.
Jaehnig, K.
McKee, G. R.
Smith, D.
Uzun Kaymak, İlker Ümit
Winz, G.
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. (C) 2010 American Institute of Physics