ITPA Topical Group on MHD, Disruptions and Control

Scope

The general scope of the ITPA Topical Group on MHD, Disruptions and Control is to provide the experimental and theoretical basis and recommendations for both conventional and advanced tokamak scenarios on next-step burning fusion devices in the areas of: β limiting MHD instabilities and their active control; disruptions (physics, prediction, avoidance and mitigation) and the connected halo currents, forces and heat loads; and plasma magnetic control (current, position, shape, error fields). In these areas the group shall coordinate collaborative research activities among international fusion research establishments, including experiments to be conducted, analysis of results, modelling and comparison with theory. The group shall also direct the application of the present understanding to modelling and assessment of ITER plasmas. Predictions for burning plasma experiments require the construction, extension and analysis of a disruption database, and contributions to other databases. In addition, research priorities for physics R&D in support of burning plasma experiments have to be identified and formulated and to be endorsed by the ITPA Coordinating Committee. Based on these activities, the Topical Group shall recommend physics guidelines and methodologies for physics and technical design of burning plasma experiments. Publications and presentations on the activities of the Topical Group to fusion journals and international conferences will be promoted.

Tasks

The tasks of the MHD, Disruptions and Control Topical Group, on the basis of operimental and theoretical studies, shall address three main topics:

• MHD instabilities and their control:
  • Limits imposed on plasma parameters, especially β, by MHD instabilities in both conventional and advanced tokamak operation, e.g., neoclassical tearing modes (NTMs), external kinks, and resistive wall modes (RWMs)
  • Active control of MHD instabilities via pressure and current profile control
  • Active control of MHD instabilities via conducting structures and additional coils
  • Interaction of MHD modes with plasma rotation, error fields and toroidal field ripple
  • Diagnostic issues related to measurement and control of MHD instabilities
• Disruptions and their mitigation:
  • Disruption characterization (e.g., thermal and current quench times, halo currents, production and quenching of runaway electrons) and its projection to future machines
  • Validation of theoretical models used in disruption studies, namely disruption prediction, avoidance and mitigation
  • Extension of the existing disruption database, especially towards q ≈ 3 discharges, quench time scales and halo current asymmetries
  • Tools and recommendations for disruption prediction, avoidance, and mitigation—both for heat loads and forces to achieve reliable machine protection
  • Assessment of disruption mitigation by techniques including pellets and strong gas puffs
  • Avoidance and mitigation of runaway electron production during current decay
  • Scenarios of emergency plasma termination (fast shut-down)
  • Diagnostic issues related to prediction, avoidance, and mitigation of disruptions
• Plasma magnetic control:
  • Recommendations on the reactor-relevant conventional and advanced tokamak scenarios
  • Plasma scenario and machine sequencing requirements to obtain the plasma target parameters and to avoid disruption
  • Feedback and feedforward control of plasma current, position and shape by axi-symmetric poloidal fields
  • Control and reduction of error fields
  • Experimental validation of theoretical models used for magnetic control simulations
  • Diagnostic issues related to magnetic control
  • Development, tests and recommendations on magnetic control used in Plasma Control Simulators. (Taking into account the high cost of ITER equipment and the cost of running a tokamak discharge, all experiments should be at first simulated and properly optimized with user-friendly numerical codes referred to as Plasma Control Simulators. Activity on the PCS includes development of codes, their validation in experiments, improvements in the codes and simulation of ITER discharges with feedforward and feedback plasma control)
• Runaway electrons:
  • Study of the generation of runaway electrons by disruptions in present devices and comparison with theory
  • Development of mitigation/control tools for ITER