Leveraging EC H&CD Spatial Variation for Enhanced Regulation of Current Profile in Tokamak

S.T. Paruchuri, E. Schuster, A. Pajares

11th ITER International School on “ITER Plasma Scenarios and Control”

San Diego, California, USA, July 25-29, 2022

Next-generation tokamaks like ITER will be required to regulate multiple plasma properties around predetermined optimal values to achieve stable plasma confinement. Complex active control strategies may have to be implemented in the Plasma Control System (PCS) to allocate the noninductive powers and achieve the required control objectives. The presence of numerous targets may force the controller to compete for noninductive powers, which are constrained by the physical saturation limits. Enhancing the regulation capability of noninductive drives may improve the regulation of plasma properties. This work demonstrates a novel approach for enhancing controller capability through active variation of the electron cyclotron heating and current drive (ECH&CD) position. Traditionally, ECH&CD are fixed during tokamak operation, i.e., the region of incidence of the waves generated by ECH&CD is not varied. However, the incidence region can be updated in real-time by varying the angle of wave reflecting mirrors. This work presents novel methods for modeling the effect of ECH&CD position on plasma dynamics. Furthermore, multiple control algorithms that exploit the ECH&CD position as a controllable variable for the safety factor control problems, including minimum safety factor regulation and local safety factor gradient control, are also presented. The effect of ECH&CD position on the controller capabilities is studied for a DIII-D tokamak scenario using nonlinear simulations carried out in the Control Oriented Transport SIMulator (COTSIM). The simulations illustrate that updating ECH&CH can prevent noninductive power saturation in certain scenarios.

*Supported by the US DOE under DE-SC0021385.