APD detector electronics for the NSTX Thomson scattering system

An electronics system has been installed and tested for the readout of avalanche photodiode (APD) detectors for the National Spherical Torus Experiment (NSTX) Thomson scattering system. Similar to previous designs, it features preamps with a fast and a slow output. The fast output uses pulse shaping to optimize sensitivity for the 8 ns scattered light pulse while rejecting noise in the intrinsic plasma background. A low readout noise of similar to 25 photoelectrons is achieved at an APD gain of 75. The design incorporates a number of features to provide flexibility for various modes of calibration. (C) 2001 American Institute of Physics.