Control of Edge Transport Barrier relaxations using Resonant Magnetic Perturbations

Abstract

In divertor tokamak plasmas, an Edge Transport Barrier forms during the L-H transition. A poloidal shear flow has been shown to play a crucial role in the barrier sustainement. The H regime, obtained for a critical value of the heating power, is promising for the next generation of tokamak experiments such as ITER. However, an instability known as Edge Localized Mode (ELM) develops as the power is increased further. ELMs are characterized by intermittent bursts in the radial heat flux, therefore causing the transport barrier to relax quasi-periodically. Over the last decade, the possibility of controlling ELMs has become more and more plausible, as recent experiments were carried out on DIII-D using I-coils, on JET using error field correction coils, and on TEXTOR using an ergodic divertor. These experimental studies demonstrate a qualitative control over the ELMs by imposing a magnetostatic perturbation at the plasma edge. However, in order to get any quantitative result, much work has to be done in the understanding of ELM dynamics. In this work, we present results from numerical simulations of Resistive Ballooning Mode (RBM) turbulence reproducing the stabilization of barrier relaxations by a static magnetic perturbation. We focus our study on the edge region around the resonant surface q = 3. We use the TEXTOR tokamak geometry, and plasma parameters close to those used in typical experiments on this machine.In divertor tokamak plasmas, an Edge Transport Barrier forms during the L-H transition. A poloidal shear flow has been shown to play a crucial role in the barrier sustainement. The H regime, obtained for a critical value of the heating power, is promising for the next generation of tokamak experiments such as ITER. However, an instability known as Edge Localized Mode (ELM) develops as the power is increased further. ELMs are characterized by intermittent bursts in the radial heat flux, therefore causing the transport barrier to relax quasi-periodically. Over the last decade, the possibility of controlling ELMs has become more and more plausible, as recent experiments were carried out on DIII-D using I-coils, on JET using error field correction coils, and on TEXTOR using an ergodic divertor. These experimental studies demonstrate a qualitative control over the ELMs by imposing a magnetostatic perturbation at the plasma edge. However, in order to get any quantitative result, much work has to be done in the ...