Pulse-Burst Laser Systems for Thomson Scattering on MST

A new purpose-built ``pulse-burst'' laser system is being constructed for the Thomson scattering diagnostic on the MST reversed-field pinch. This new laser will produce a burst of 1--2 J $Q$-switched pulses at repetition rates 5--250 kHz. It will operate at 1064 nm and is a master oscillator, power amplifier (MOPA) system. Variable pulse-width drive (0.15--20 ms) of the flashlamps in this laser will be accomplished by IGBT switching of large electrolytic capacitor banks. A subset of these power supplies has already been constructed and is currently being used to drive the flashlamps in the two existing commercial Nd:YAG lasers used for Thomson scattering on MST. Each of these upgraded lasers now produces a burst of up to fifteen 2 J $Q$-switched pulses (1064 nm) at repetition rates 1--12.5 kHz. Direct control of the laser Pockels cell drive enables optimal pulse energy extraction, and up to four 2 J laser pulses during one flashlamp pulse. These lasers are currently being used to study the dynamic evolution of electron temperature in MST. The new purpose-built ``pulse-burst'' laser system will further expand this capability.