Design of a new Nd:YAG Thomson scattering system for MAST^a)

A new infrared Thomson scattering system has been designed for the MAST tokamak. The system will measure at 120 spatial points with $≈10mm$ resolution across the plasma. Eight 30 Hz 1.6 J Nd:YAG lasers will be combined to produce a sampling rate of 240 Hz. The lasers will follow separate parallel beam paths to the MAST vessel. Scattered light will be collected at approximately $f/6$ over scattering angles ranging from $80°$ to $120°$⁠. The laser energy and lens size, relative to an existing 1.2 J $f/12$ system, greatly increases the number of scattered photons collected per unit length of laser beam. This is the third generation of this polychromator to be built and a number of modifications have been made to facilitate mass production and to improve performance. Detected scattered signals will be digitized at a rate of 1 GS/s by 8 bit analog to digital converters (ADCs.) Data may be read out from the ADCs between laser pulses to allow for real-time analysis.