The control of large scale magnetic instabilities in fusion plasmas is essential for the successful operation of ITER and future fusion power plants. Large scale numerical simulations on the largest supercomputers are applied to study the physics of these instabilities, their consequences and the methods for control.

Simulations of instabilities in fusion plasmas, developing the predictive capability for their occurrence, consequences and control, are required for the preparation of operation of ITER and design of future machines

Fusion plasmas can suffer from global instabilities of the magnetic structure of the plasma. The so-called magnetohydrodynamic (MHD) instabilities, driven unstable by the plasma pressure and current, can cause fast losses of the thermal plasma energy. A typical time scale is of the order of 100ms to 1ms.

In present tokamak experiments the effect of the fast MHD induced energy losses to the first wall are mostly tolerable. However, in ITER and future fusion power plants the resulting heat fluxes are likely to be beyond the melting limits of the plasma facing components.

Large-scale computer simulation can give valuable insight in the underlying physics of MHD instabilities as well as the methods for their control. For this purpose, the MHD simulation code JOREK is under development within the European fusion program (www.jorek.eu). The JOREK code is unique in that it combines a (MHD) fluid description of the main plasma with realistic description of the plasma wall interaction. This includes a particle model for neutrals and impurities, describing the sputtering, ionization, recombination and collisions.

The main applications include so-called Edge Localised Modes (ELMs), radiative instabilities leading to disruptions and MHD instabilities driven unstable by the population of fast particles in the plasma originating from fusion reactions and external heating.