Towards Density Profile Regulation via Pellet Injection in Tokamaks Following a Hybrid Model Predictive Control Approach

L. Yang, H. Al Khawaldeh, S.T. Paruchuri, X. Song, Z. Wang, E. Schuster

29th IAEA Fusion Energy Conference

London, UK, October 16-21, 2023

Abstract

A hybrid model predictive control (MPC) strategy accounting for the discrete-time nature of pellet injection is developed to actively regulate the plasma-density profile in a cylindrical geometry. Pellet injection is expected to be the primary fueling system of next-generation tokamaks such as ITER. This is due to its ability to overcome the limitations associated with gas puffing, such as the time delay in actuation caused by the machine’s size and the inability of the neutral fueling gas to penetrate the plasma core. In this work, the discrete-time nature of pellet injection is taken into account during the synthesis of the density-profile controller. The pellet-injection system dynamics is approximated by a simple discrete-time model that intends to reproduce the fueling effects of the injected pellets in tokamaks like ITER. The density-profile evolution model, given by a one-dimensional partial differential equation, is discretized in space and time to reduce it into a set of difference equations to enable MPC design. The MPC scheme is designed by solving a finite-horizon optimization control problem that incorporates constraints on both the plasma state and the control inputs. Simulation studies are conducted to analyze the controller’s performance.