Mechanisms of edge-localized-mode mitigation by external-magnetic-field perturbations

Resonant pedestal pressure reduction induced by a thermal transport enhancement due to stochastic magnetic boundary layers in high temperature plasmas

Good alignment of the magnetic field line pitch angle with the mode structure of an external resonant magnetic perturbation (RMP) field is shown to induce modulation of the pedestal electron pressure p(e) in high confinement high rotation plasmas at the DIII-D tokamak with a shape similar to ITER, the next step tokamak experiment. This is caused by an edge safety factor q95 resonant enhancement of the thermal transport, while in contrast, the RMP induced particle pump out does not show a significant resonance. The measured p(e) reduction correlates to an increase in the modeled stochastic layer width during pitch angle variations matching results from resistive low rotation plasmas at the TEXTOR tokamak. These findings suggest a field line pitch angle resonant formation of a stochastic magnetic edge layer as an explanation for the q95 resonant character of type-I edge localized mode suppression by RMPs.

Sheared plasma rotation in partially stochastic magnetic fields

It is shown that resonant magnetic perturbations generate sheared flow velocities in magnetized plasmas. Stochastic magnetic fields in incomplete chaos influence the drift motion of electrons and ions differently. Using a fast mapping technique, it is demonstrated that a radial electric field is generated due to the different behavior of passing particles (electrons and ions) in tokamak geometry; magnetic trapping of ions is neglected. Radial profiles of the polodial velocity resulting from the force balance in the presence of a strong toroidal magnetic field are obtained. Scaling laws for plasma losses and the forms of sheared plasma rotation profiles are discussed.

Elucidation of the heat-flux limit from magnetic-island heating

Recent experiments on heating of magnetic islands in a tokamak are analyzed to assess plasma transport characteristics. By comparing with the experimental data, both perpendicular and parallel components of the electron heat conductivity in the island are determined. As a consequence, the so-called heat-flux limit factor xi, the ratio of the parallel heat conduction flux in a collisionless plasma to that transferred by free-streaming electrons, can be estimated. The found factor xi does not contradict that established earlier by interpreting laser plasma experiments.