Discussion of Nonlinear Energetic Particle Issues

Boris Breizman

Institute for Fusion Studies

A population of energetic particles in plasma can excite instabilities with potentially adverse consequences for particle and energy confinement. The related theoretical picture has to be intrinsically nonlinear since instability growth times are typically much shorter than the plasma lifetime. There has been a significant progress in recent years in understanding key physics elements that control the nonlinear evolution of unstable modes. This understanding has been instrumental in the interpretation of challenging observations made on JET and TFTR. It has also led to the development of first-principle reduced numerical models. It is quite possible that, with this background, the nonlinear studies will raise to the level of credible assessment of collective effects associated with energetic particles in burning plasma. This will require a substantial expansion of numerical work to accomplish a transition from idealized models that focus on the essential physics, to fully realistic modeling relevant to specific fusion devices.