Status of the control system on the National Spherical Torus Experiment (NSTX)

In 2003, the National Spherical Torus Experiment (NSTX) plasma control system was used for plasma shape control using real-time equilibrium reconstruction (using the rtEFIT code). rtEFIT is now in routine use for plasma boundary control. More recently, the system has been upgraded to support feedback control of the resistive wall mode (RWM). This paper describes the hardware and software improvements that were made in support of these physics requirements. The control computer is an eight processor embedded system. The real-time data acquisition system now acquires 352 channels of data at 5kHz for each NSTX plasma discharge. The latency for the data acquisition, which uses the Front Panel Data Port (FPDP) protocol, is measured to be ∼8μs. A Stand-Alone Digitizer (SAD), designed at PPPL, along with an FPDP Input Multiplexing Module (FIMM) allows for simple modular upgrades. An interface module was built to interface between the FPDP output of the NSTX control system and the legacy Power Conversion Link (PCLink) used for communicating with the PPPL power supplies (first used for TFTR). Additionally a module has been built for communicating with the switching power amplifiers (SPA) recently installed on NSTX. In addition to the hardware developments, the control software on the NSTX control system has been upgraded. The device driver software for the hardware described above will be discussed, as well as the new control algorithms that have been developed to control the switching power supplies for RWM control. A reliable mode detection algorithm for RWM feedback is currently under development.