Current status of DIII-D real-time digital plasma control

This paper describes the current status of real-time digital plasma control for the DIII-D tokamak. The digital plasma control system (PCS) has been in place at DIII-D since the early 1990s and continues to expand and improve in it's capabilities to monitor and control plasma parameters for DIII-D fusion science experiments. The PCS monitors over 200 tokamak parameters from the DIII-D experiment using a real-rime data acquisition system that acquires a new set of samples once every 60 mu s. This information is then used in a number of feedback control algorithms to compute and control a variety of parameters including those affecting plasma shape and position. A number of recent improvements to the control capabilities of the PCS along with general system enhancements have contributed to the advancement and understanding of fusion energy science at DIII-D. Among the more significant improvements to the PCS control capabilities has been the successful incorporation of advanced techniques for reconstruction of plasma equilibrium parameters in realtime. An isoflux control method using these improved plasma parameter calculations has greatly enhanced the ability of achieving desired shaped plasma on the DIII-D tokamak and even made it possible to achieve new and different ones. A number of system related improvements has improved the usability and flexibility of the DIII-D PCS. These include more graphical user interfaces to assist in entering and viewing the large and ever growing number of parameters controlled by the PCS, increased interaction and accessibility from other DIII-D applications, and upgrades to the computer hardware and vended software. Future plans for the system include possible upgrades of the real-time computers, further links to other DIII-D diagnostic measurements such as real-time Thomson scattering analysis, and joint collaborations with other tokamak experiments including the NSTX at Princeton.