Simserver simulation of a model-based current profile controller in the DIII-D Plasma Control System

Abstract Setting up a suitable current profile, characterized by a weakly reversed magnetic shear, has been demonstrated to be a key condition for one possible advanced tokamak operating scenario with improved confinement and possible steady-state operation. Experiments at DIII-D focus on creating the desired current profile during the plasma current ramp-up and early flat-top phases with the aim of maintaining this target profile throughout the subsequent phases of the discharge. The evolution in time of the current profile, or alternatively the safety factor q, is related to the evolution of the poloidal flux, which is modeled in normalized cylindrical coordinates using a partial differential equation referred to as the magnetic flux diffusion equation. A control-oriented model of the current profile evolution in DIII-D was recently developed for the plasma current ramp-up and early flat-top phases and used to synthesize both open-loop and closed-loop control schemes. In this work, we report on the implementation of an advanced model-based current profile controller in the DIII-D Plasma Control System (PCS) and on the assessment of this controller implementation in closed-loop Simserver (simulation server) simulations.