Development of an Active Plasma Control System for Pegasus

The Phase II Pegasus ST experiment includes fully programmable power supplies for all magnet coils. These will be integrated with a digital feedback plasma control system (PCS), based on the PCS in use on DIII-D, to provide active feedback control of the plasma evolution. The initial goal is to control I$_{p}$(t), R(t), and Z(t). The feedback cycle consists of: 1) sampling magnetic diagnostics, 2) applying a response matrix derived from equilibrium reconstructions, 3) accounting for induced vessel currents and power supply frequency responses, and 4) adjusting the current demand, all on a timescale that is fast compared to the shot duration of $\sim $25 ms. Data is sampled via a 500 kHz, 96-channel CPCI digitizer from DTACQ Solutions, Ltd. The power supply control signals are generated by 16 analog waveform generators, with the option to utilize 32 digital I/O lines in the future. The PCS digitizer is controlled via a system of Linux-based computers that perform requisite computation-intensive tasks and interface to the existing LabVIEW control codes via a TCP/IP network link.