Papers for

fusion plant operators

Papers whose findings have a practical use for this group, as judged from the abstract. Open a paper to read what it means in practice.

Reinforcement learning controls tokamak plasma shape and density ramps

Reinforcement Learning Controllers for Fusion Scenario Development

Abstract: Scenario development, the design of the waveforms that take a tokamak discharge from breakdown to flat-top, is still an iterative, labour-intensive process. Every candidate scenario has to be simulated with a controller in the loop, and the classical shape and current controllers need low-level actuator references. So the process is iterative and includes a number of trial-and-error steps. We propose to replace the per-scenario controller tuning by a single goal-conditioned reinforcement-learning controller trained once, in advance, against a free-boundary equilibrium and transport simulator. A scenario is then specified only by the target waveforms of the physical quantities of interest (plasma current, line-averaged electron density, LCFS shape, x-point positions), and the controller produces the coil-current and fueling commands that realize them. We demonstrate the approach on an EAST plasma-current ramp-up: the controller takes over a small limited plasma, ramps the current and the density, grows the cross-section, forms two x-points and holds a double-null diverted configuration against sampled shape targets for the rest of a 1.2 s episode. The neural network controller is trained using TQC algorithm. On 1024 test scenarios sampled from a low-discrepancy scrambled Sobol sequence in 11-dimensional target space, the controller forms the divertor in 86% of the cases, holds it for more than 0.5 s in 67% and reaches the end of the episode in a diverted state in 58%, with flat-top tracking errors of a few kA in plasma current, $\sim 0.15\times10^{19}$ m$^{-3}$ in density, $\sim 2$ cm in position and $\sim 8$ cm in x-point location; the failures concentrate at the high-current density ($J$) region which is believed to be physically or from engineering perspective not feasible within ohmic mode.

Mon 19 OctMachine Learning
The gist
Designing waveforms to guide fusion plasma in tokamaks is usually slow and requires many manual adjustments. The authors propose training a single AI controller beforehand to handle many scenarios, making the process faster and less trial-and-error. This AI learns to produce control commands that achieve target plasma properties like current and shape. They tested it in a simulated tokamak ramp-up, showing the controller can achieve and maintain complex shapes in most cases with reasonable accuracy.
Open → 2610.26138v1