New DSP-based firing generator for the PPPL AC/DC converters

The control systems of the National Spherical Tokamak Experiment (NSTX) are undergoing a significant upgrade. The new digital firing generator (FG) is a key component. The new FG is designed and implemented using two Texas Instrument (TI) digital signal processors (DSP) which accept the firing angle, convert and bypass command from the real time computer using the Front Panel Data Port (FPDP) protocol. It generates the six firing pulses to the thyristor power supplies for the NSTX magnet coils that operate with a variable frequency AC source. This paper provides a detailed description of the FG system, the optical communication link, the phase lock loop circuit and the DSP hardware and software. Some test results using the new FG for the power supply are also included.