Kinetic estimate of the shielding of resonant magnetic field perturbations by the plasma in DIII-D

Abstract

Effects of linear plasma response currents on non-axisymmetric magnetic field perturbations from the I-coil used for Edge Localized Mode mitigation in DIII-D tokamak are analyzed with the help of a kinetic plasma response model developed for cylindrical geometry. It is shown that these currents eliminate the ergodization of the magnetic field in the core plasma and reduce the size of the ergodic layer at the edge. A simple balance model is proposed which qualitatively reproduces the evolution of the plasma parameters in the pedestal region with the onset of the perturbation.It is suggested that the experimentally observed density pump-out effect in the long mean free path regime is the result of a combined action of ion orbit losses and magnetic field ergodization at the edge.

Impact of screening of resonant magnetic perturbations in three dimensional edge plasma transport simulations for DIII-D

“…16 of introducing ad hoc helical current sheets on resonant magnetic surfaces. As there are indications that RMPs are (partially) screened inside the plasma, [17][18][19] we consider the case of weak RMP penetration and compare this to the extreme cases of full penetration (i.e., no screening, the vacuum approximation) and full screening (i.e., the axisymmetric configuration without RMPs).…”

Plasma transport in stochastic magnetic field caused by vacuum resonant magnetic perturbations at diverted tokamak edge

“…Under fixed externally applied RMP fields, the present study includes most of the relevant transport physics selfconsistently, but assumes that the electrostatic potential Φ variations within a flux surface and the RMP-induced changes to turbulence transport are negligible. Plasma screening is suspected to play an important role in the actual RMP distribution, but is difficult to calculate [17][18][19][20][21]. Numerical simulation of plasma screened RMPs, self-consistently with kinetic plasma dynamics, electric field response and plasma rotation, is currently under invetigation and will be a subject of a future report.…”

On the confinement of passing alpha particles in a tokamak-reactor with resonant magnetic field perturbations shielded by plasma currents

“…Predictions of such shielding by linear kinetic 5 and drift MHD 6 models agree by order of magnitude. As a result of the shielding, the island width which follows from the vacuum model for the perturbation field is reduced up to two orders of magnitude.…”

“…One of the most likely reasons is that the perturbations are strongly shielded by plasma response currents at resonant rational magnetic surfaces 5 . Predictions of such shielding by linear kinetic 5 and drift MHD 6 models agree by order of magnitude.…”

“…5. This model has been used earlier for the estimation of RMP effects on the magnetic configuration in the presence of a plasma typical for experiments on ELM mitigation in DIII-D.…”