Design and operation of the multipulse Thomson scattering diagnostic on DIII-D (invited)

Publisher Website
Google Scholar
Abstract
This paper describes 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. As many as eight lasers may be fired alternately for an average measurement frequency of 160 Hz, or they may be fired in rapid succession (L–H transitions, edge localized modes (ELMs), beta limits, transport, and disruptions in an efficient manner suitable for large tokamak operation where shot‐to‐shot scans are impractical. The scattered light is dispersed by interference filter polychromators and detected by silicon avalanche photodiodes. Laser control and data acquisition are performed in real time by a VME‐based microcomputer. Data analysis is performed by a MicroVAX 3400. Additional features of this system include real‐time analysis capability, full statistical treatment of error bars based on the measured background light, and laser beam quality and alignment monitoring during plasma operation. Results of component testing, calibration, plasma operation, and error analysis are presented.