Modeling of edge control by ergodic fields in DIII-D, JET and ITER

The reduction of the heat and particles loads on the Plasma Facing Components (PFCs) due to Type I Edge Localized Modes (ELMs) remains a significant research problem for the international tokamak program. Among the possible approaches of ELMs control is the use of an external perturbing coils to ergodise the edge magnetic fields, thereby increasing the thermal and particle losses in the region of the H-mode barrier and ensuring that the pressure gradient required to trigger Type I ELMs is never attained. A resonant magnetic perturbation (RMP) generated by I-coils in DIII-D has been proven to be able to suppress the type I ELMs reliably without significant degradation of plasma confinement [R. Moyer, et al., Phys. of Plasmas 12, 05611 (2005)]. The paper presents recent modeling results of the Type I ELMs control using stochastic boundaries for the possible future ITER and JET control systems using the realistic experiment in DIII-D as a reference case. A number of possible designs of the external and in-vessel coils ITER are analyzed taking into account physical, technical and space constraints. For typical H-mode scenario and six upper and six lower coils (n=3) configuration ∼400 kA current is needed for external coils and ∼20 kA for in-vessel coils mounted on the blanket modules in order to generate DIII-D-like magnetic perturbation spectrum in ITER. The heat transport and Type I ELMs suppression modelling in the presence of the external magnetic perturbation was done using non-linear code TELM [M. Becoulet, et al., Nucl. Fusion, 45 (2005) 1284] for DIII-D, JET and ITER. The mechanism of the increased heat transport in ergodic fields is the appearance of a radial component of the heat flux parallel to the field lines, due to the radial component of the magnetic field. The first results based on the nonlinear MHD modeling in X-point geometry [G. Huysmans, Plasma Phys. Control Fus. 47 (2005) 2107] taking self-consistent plasma response on the external magnetic perturbation are presented. The most important mechanism of the pressure reduction in the presence of the magnetic perturbation identified is the plasma density transport due to the E x B drift. It was demonstrated that an amplification of the external magnetic perturbation is possible near the threshold for tearing modes. (author)