Nonlinear Adaptive Burn Control of Two-Temperature Tokamak Plasmas

V. Graber and E. Schuster

58th IEEE Conference on Decision and Control

Nice, France, December 11-13, 2019

Abstract

Generating electricity by harnessing the en- ergy released from nuclear fusion reactions is an emerging environmentally-friendly approach. A tokamak is a toroidal device where a hot ionized gas, or plasma, is magnetically confined at temperatures suitable for nuclear fusion. Future commercial tokamaks will require proper control of external actuators, such as particle injection and auxiliary heating, to regulate the density and temperature of burning (fusion producing) plasmas. This is known as burn control, and it is one of the greatest challenges in fusion reactors. Engineering limitations may force upcoming reactors, such as ITER, to operate at conditions where the thermonuclear reaction rate increases as the plasma temperature increases. Plasma operation necessitates active control schemes to precisely regulate the nonlinear burning plasma dynamics. Controllers based on lin- earized models may fail under large perturbations. Therefore, control designs that consider the nonlinearities of the multi- variable plasma dynamics are indeed necessary. In this work, a control algorithm is proposed based on a nonlinear, volume- averaged, two-temperature model. This zero-dimensional (0D) model consists of particle and energy conservation equations. Since plasmas are highly complex systems, any reduced control-oriented model is bound to contain uncertainty. The considered model contains uncertainties in the relationship between the ion and electron temperatures, the plasma confinement scalings, and the particle recycling that results from plasma-wall interactions. Adaptive control laws are employed to stabilize the system despite these numerous uncertainties. A simulation study illustrates the effectiveness of the presented adaptive controller.