Closed loop control of the sawtooth instability in nuclear fusion

Abstract

In nuclear fusion the sawtooth instability is an important plasma phenomenon, having both positive and negative effects on the tokamak plasma. Control of its period is essential in future nuclear fusion reactors. This paper presents a control oriented model of the sawtooth instability, with current drive as input and sawtooth period as output, and validates it with a more extended model and experimental data. This model is numerically implemented and combined with PI-controllers in a feedback loop. Simulations show that closed loop control of the system to a desired sawtooth period is indeed possible, even when time delay is added to the feedback loop.

Systematic design of a sawtooth period feedback controller using a Kadomtsev–Porcelli sawtooth model

“…The transition is around the q = 1 surface. These results are in good agreement with previous publications [13,14,29]. Hence, the ECCD actuated current diffusion mechanism of our model is sufficient to capture the basic sawtooth behaviour.…”

“…A control-oriented model should capture the relevant static and dynamic input-output behaviour of a system with a minimal amount of complexity. Therefore, our model (a continuation of the work in [29]) is solely based on the evolution of the poloidal magnetic field B θ (r, t) over the radial coordinate r and time t. For large aspect-ratio tokamaks the toroidal magnetic field B φ can be assumed constant, so that the poloidal field B θ uniquely defines the safety factor q and magnetic shear s [30], since…”

Real-time wavelet detection of crashes in limit cycles of non-stationary fusion plasmas

“…Some control experiments and simulations for the sawteeth period have been presented in the literature [3][4][5][10][11][12][13]. Most of the above-mentioned experiments were carried out in open-loop and some in closed-loop, but a systematic optimization of the overall control loops (which includes the sensor) has not been presented.…”