Timing and triggering of the Thomson scattering diagnostics on the COMPASS tokamak

The Thomson scattering diagnostics (TS) at the COMPASS tokamak (operated in the Institute of Plasma Physics ASCR, Prague, Czech Republic) is based on two high-power Nd:YAG lasers, which have a pulse energy of 1.5J and repetition rate of 30 Hz each. A new timing and synchronization unit (TSU) based on a Field Programmable Gate Array (FPGA) was designed and constructed in order to assure reliable and synchronized control of flash lamps and Q-switches of both lasers. Correct delay between laser pulses is necessary to obtain the highest possible laser energy and to prevent the active medium, the Nd:YAG rod, from thermal damage. An FPGA development kit was chosen as core hardware for the TSU and dedicated input and output circuits were manufactured to adapt the kit interfaces for COMPASS TS needs. In addition, the FPGA firmware, the control software, and the graphical user interface were developed to control the TSU hardware. This paper describes the TS regimes that are addressed by the new TSU. Further, the TSU design, the operation flow, and the firmware and software development are presented. Finally, the results of commissioning are shown. (C) 2014 Institute of Plasma Physics AS CR Published by Elsevier B.V. All rights reserved.