David J. Campbell

The International Tokamak Physics Activity (ITPA) has developed a comprehensive overview of the results of its coordinated R&D activities in fusion physics and diagnostics implemented during the past two decades with the aim of developing an improved physics basis for the operation of tokamak burning plasma experiments. Here, an introduction is presented to key concepts in the physics of burning plasmas in tokamaks, together with an overview of the scope of the principal areas of physics R&D pursued by the ITPA Topical Physics Groups in which the critical issues, major areas of progress and most significant recent results are highlighted. This paper introduces the following collection of articles, which encompass detailed presentations of the progress achieved by the Topical Groups in preparing the physics basis for the operation of tokamak burning plasma experiments expected to come into operation in the 2030s.

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The fast loss of thermal and magnetic energy during an unmitigated disruption in ITER can lead to heat fluxes exceeding melt thresholds for plasma facing components, can generate high electromagnetic loads in some cases close to the design limits, and can potentially cause the generation of high energy runaway electrons. Therefore, the operation strategy in ITER will have a strong focus on limiting the number of disruptions and especially of those that are unmitigated. This will be achieved by a multi-layer strategy including disruption prevention and avoidance, disruption prediction and disruption mitigation. The plasma control system (PCS) will be in charge to react to any deviation from the predicted behavior by applying appropriate correction measures for which an extensive suite of actuators is available including those for active disruption prevention like electron cyclotron heating. It is also the PCS that optimizes triggering of the disruption mitigation system (DMS), should a disruption be imminent despite all control efforts. This paper will give an overview on all aspects of disruption control with a more detailed discussion of the requirements for the DMS.