The multipulse Thomson scattering diagnostic on the DIII-D tokamak

The authors describe the design and operation of a 40 spatial channel Thomson scattering system that uses multiple 20-Hz Nd:YAG lasers to measure the electron temperature and density profiles periodically throughout an entire plasma discharge. Interference filter polychromators disperse the scattered light, which is detected by silicon avalanche photodiodes. The measurable temperature range is from 10 eV to 20 keV, and the minimum detectable density is about 2×10 ¹⁸ m^-3. Laser control and data acquisition are performed in real time by a VME-based microcomputer. Data analysis is performed by a MicroVAX 3400. Unique features of this system include burst mode operation, where multiple lasers are fired in rapid succession (<10 kHz), real-time analysis capability, and laser beam quality and alignment monitoring during plasma operation. Results of component testing, calibration, and plasma operation are presented