Upgrades to improve the usability, reliability, and spectral range of the MST Thomson scattering diagnostic

Abstract

The Thomson scattering diagnostic on MST records both equilibrium and fluctuating electron temperature with a range capability of 10 eV-5 keV. Standard operation with two modified commercial Nd:YAG lasers allows measurements at rates of 1 kHz-25 kHz. Several subsystems of the diagnostic are being improved. The power supplies for the avalanche photodiode detectors (APDs) that record the scattered light are being replaced to improve usability, reliability, and maintainability. Each of the 144 APDs will have an individual rack mounted switching supply, with bias voltage adjustable to match the APD. Long-wavelength filters (1140 nm center, 80 nm bandwidth) have been added to the polychromators to improve capability to resolve non-Maxwellian distributions and to enable directed electron flow measurements. A supercontinuum (SC) pulsed white light source has replaced the tungsten halogen lamp previously used for spectral calibration of the polychromators. The SC source combines substantial brightness produced in nanosecond pulses with a spectrum that covers the entire range of the polychromators.