Real-time control software on NSTX

The National Spherical Tokamak Experiment (NSTX) depends on high speed, real-time control to establish initial magnetic field configurations, drive plasma current, and control plasma position and shape. The control required on NSTX is achieved through the combined efforts of several applications developed collaboratively including the power supply real-time controller (PSRTC) and the plasma control system (PCS). The PSRTC communicates with the PCS receiving from the PCS real-time voltage controls and is responsible for supplying dc power to the NSTX poloidal field, toroidal field and Ohmic heating coils. The PCS, which was designed at general atomics, controls the data acquisition, gas injection, plasma current, and plasma shape, including a real-time EFIT and isoflux algorithm for equilibrium reconstruction. Modular control algorithms, specific to NSTX, were written and incorporated into the PCS. The NSTX control system is equipped with 160 channels of fast real-time data acquisition and eight 333 MHz G4 processors, which perform the supervision, position, shape, and performance control. After a discharge, the acquired data and setup parameters are transferred to an MDSPlus central archive for later inspection and can be used to repeat previous machine configurations.