Recent progress from the DIII-D program

Abstract

Significant progress has been made in a number of key scientific and engineering areas that are critical to advanced tokamak operation on the DIII-D tokamak. Improved error field correction coupled with plasma rotation has resulted in a passive wall stabilized discharge at twice the no-wall beta limit. Active feedback stabilization of the resistive wall mode (RWM) has been improved using newly installed internal magnetic sensors and external control coils. A set of internal control coils for RWM feedback has been designed that should permit operation at close to the ideal limit. Real-time stabilization of the neoclassical tearing mode has been achieved using a new "search and suppress" control algorithm coupled with electron cyclotron current drive (ECCD). The ECCD system is routinely providing in excess of 2 MW of power for 2 s pulses. Modeling predicts that measured efficiencies of ECCD are consistent with future, fully non-inductive AT target discharges. Massive injection of Ar gas has resulted in successful mitigation of disruptions in high performance discharges without producing high energy runaway electrons. Finally, an upgraded digital plasma control system will provide significantly more capability to provide real time measurement and control of plasma profiles and instabilities.