Progress in disruption prevention for ITER

Abstract

Key plasma physics and real-time control elements needed for robustly stable operation of high fusion power discharges in ITER have been demonstrated in US fusion research. Optimization of the current density profile has enabled passively stable operation without n " 1 tearing modes in discharges simulating ITER's baseline scenario with zero external torque. Stable rampdown of the discharge has been achieved with ITER-like scaled current ramp rates, while maintaining an X-point configuration. Significant advances have been made toward real-time prediction of disruptions: machine learning techniques for prediction of disruptions have achieved 90% accuracy in offline analysis, and direct probing of ideal and resistive plasma stability using 3D magnetic perturbations has shown a rising plasma response before the onset of a tearing mode. Active stability control contributes to prevention of disruptions, including direct stabilization of resistive-wall kink modes in high-β discharges, forced rotation of magnetic islands to prevent wall locking, and localized heating/current drive to shrink the islands. These elements are being integrated into stable operating scenarios and a new event-handling system for off-normal events in order to develop the physics basis and techniques for robust control in ITER.

Investigating the Physics of Tokamak Global Stability with Interpretable Machine Learning Tools

“…In the last couple of years, therefore, many efforts have been devoted to the developments of parsimonious data-driven techniques that can provide a good success rate of prediction after a few tens of disruptions and even after the first disruption [19][20][21]. Their future application is very promising, particularly if coupled with new methods to avoid disruptions [22][23][24] and to model the stability boundary [25].…”

Fully Convolutional Spatio-Temporal Models for Representation Learning in Plasma Science

“…In many toroidal plasma devices such as tokamaks and spherical toruses (STs) (Gerhardt et al, 2013), disruptions are observed as sudden and dangerous events that induce rapid release of particles and energy to the device wall (Schuller, 1995). A typical disruption brings the plasma experiment (the "shot") to an abrupt end and, because of the associated large rapid energy release, it can also seriously damage the device-especially in larger systems such as ITER (Strait et al, 2019). Accordingly, the development of a plasma control system (PCS) with the ability to reliably detect and subsequently mitigate or avoid the majority of the disruption events (Hollmann et al, 2015) is broadly regarded as the most important milestone for establishing the viability of future larger tokamak devices to deliver a fusion energy reactor.…”

Likelihood Identification of High-Beta Disruption in JT-60U

“…Disruption is a serious threatening event in tokamak plasmas, resulting in large electromagnetic and thermal loads on structural components of a tokamak device. In order to avoid critical damage of a device and ensure reliable operation, prediction, avoidance, and mitigation of disruption are crucial issues, in particular, in ITER [1,2] as well as a future tokamak fusion reactor. Disruption is caused by a variety of magnetohydrodynamics (MHD) instabilities [3,4], where major driving forces are the gradients of plasma currents and pressure.…”