H-mode barrier control with external magnetic perturbations

While present plasma scenarios rely on self generated plasma conditions, active control with ergodic divertor coils provide the means to operate in H-mode with divertor and SOL plasma conditions that are compatible with the technical constraints. The stochastisation of field lines in the vicinity of the separatrix, will produce a localized enhancement of electron heat transport. This will provide a control on the edge temperature,(and thus pressure) barriers. Consequently, the local current profile, which is essentially bootstrap, will be modified. H-mode edge barriers can be controlled and type I Elms avoided in this way. Such controls are required for advanced regimes. The paper will discuss this in light of the theoretical and experimental advances of the last years: Tore Supra experiments gave evidence of the fine tuning capability of the perturbation on a well defined magnetic configuration while JFT-2M experiments showed that the edge stochastisation of the X point configuration has widened the operating windows of the type III ELM regime. The possible implementations of such control in a medium size tokamak (DIII-D) and eventually on ITER will also be described. (C) 2003 Elsevier Science B.V. All rights reserved