RMP ELM suppression in DIII-D plasmas with ITER similar shapes and collisionalities

Abstract

Large Type-I Edge Localized Modes (ELMs) are completely eliminated with small n = 3 resonant magnetic perturbations (RMP) in low average triangularity, " = 0.26, plasmas and in ITER Similar Shaped (ISS) plasmas, " = 0.53, with ITER relevant collisionalities v e " # 0.2. Significant differences in the RMP requirements and in the properties of the ELM suppressed plasmas are found when comparing the two triangularities. In ISS plasmas, the current required to suppress ELMs is approximately 25% higher than in low average triangularity plasmas. It is also found that the width of the resonant q 95 window required for ELM suppression is smaller in ISS plasmas than in low average triangularity plasmas. An analysis of the positions and widths of resonant magnetic islands across the pedestal region, in the absence of resonant field screening or a self-consistent plasma response, indicates that differences in the shape of the q profile may explain the need for higher RMP coil currents during ELM suppression in ISS plasmas. Changes in the pedestal profiles are compared for each plasma shape as well as with changes in the injected neutral beam power and the RMP amplitude. Implications of these results are discussed in terms of requirements for optimal ELM control coil designs and for establishing the physics basis needed in order to scale this approach to future burning plasma devices such as ITER.

ELM control strategies and tools: status and potential for ITER

“…Density pump-out could be minimized at DIII-D and to some level compensated the by injection of small pellets; however pellet fuelling at a high rate lead to the increase of plasma collisionality and the re-appearance of type-I ELMs [62]. Strong gas puffing or pellet fuelling recovered the lost density at JET but at the expense of a reduced confinement (gas) or introducing additional ELMs (pellets) [64].…”

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

“…The large type-I ELMs would represent a particular concern for the ITER divertor if they were not controlled [1], and the application of external Resonant Magnetic Perturbations (RMPs) is one of the most promising method to control them. Indeed, the total suppression of the type-I ELMs by RMPs was demonstrated in DIII-D [2,3] and later in ASDEX upgrade [4] and KSTAR [5]; the strong mitigation of the ELM size was also obtained in the JET [6], MAST [7] and NSTX [8] tokamaks, motivating the use of this method in ITER [2,9]. The non-linear MHD theory and modeling made significant progress to refine the understanding of the RMP interaction with the plasma [10][11][12][13][14][15].…”

Resonant Pedestal Pressure Reduction Induced by a Thermal Transport Enhancement due to Stochastic Magnetic Boundary Layers in High Temperature Plasmas

“…Therefore, the control of the ELM instabilities is a high priority physics issue for ITER. Using a periodic perturbation of the field line trajectories forming a stochastic magnetic edge layer applies a generic physics mechanism for improvement of this man-made high energy state.The complete suppression of type-I ELMs by application of small edge RMP fields, having a dominant toroidal mode number n ¼ 3, was demonstrated at DIII-D [6] and explored for ITER similar shape (ISS) plasmas with high averaged triangularity " $ 0:5 at ITER-relevant, low pedestal electron collisionality à e $ 0:1 [7]. This led to a proposal for a RMP coil set for ITER [8]; for preparation of this undertaking, plans are being made to equip practically every large tokamak in the world with RMP coils.…”

“…This new finding was confirmed for comparable discharges at fixed q 95 ¼ 3:5, i.e., the most reliable ELM suppression working point. As the actual values of T e , n e , and p e depend strongly on wall condition [19], collisionality [16], and plasma shape [7], the results are taken from discharge FIG. 1 (color).…”