Enhanced confinement scenarios without large edge localized modes in tokamaks: control, performance, and extrapolability issues for ITER

Abstract

Large edge localized modes (ELMs) typically accompany good H-mode confinement in fusion devices, but can present problems for plasma facing components because of high transient heat loads. Here the range of techniques for ELM control deployed in fusion devices is reviewed. Two strategies in the ITER baseline design are emphasized: rapid ELM triggering and peak heat flux control via pellet injection, and the use of magnetic perturbations to suppress or mitigate ELMs. While both of these techniques are moderately well developed, with reasonable physical bases for projecting to ITER, differing observations between multiple devices are also discussed to highlight the needed community R&D. In addition, recent progress in ELM-free regimes, namely quiescent H-mode, I-mode, and enhanced pedestal H-mode is reviewed, and open questions for extrapolability are discussed. Finally progress and outstanding issues in alternate ELM control techniques are reviewed: supersonic molecular beam injection, edge electron cyclotron heating, lower hybrid heating and/or current drive, controlled periodic jogs of the vertical centroid position, ELM pace-making via periodic magnetic perturbations, ELM elimination with lithium wall conditioning, and naturally occurring small ELM regimes.

Observation of Flat Electron Temperature Profiles in the Lithium Tokamak Experiment

“…Methods to reduce edge neutrals without Li can also cause beneficial changes to the pedestal, reducing pedestal density and collisionality and changing the bootstrap current and density pedestal structure in C-Mod, JET, and AUG [21][22][23]. In both NSTX and the devices without Li, peeling-ballooning stability improved, allowing a higher temperature and pressure pedestal and improving confinement [24][25][26]. While no previous experiment has directly measured the hot edge, flat temperature profile, low-recycling regime, modeling of TFTR improved confinement discharges was consistent with many of the key predictions of the low-recycling theory [1,2].…”

Scaling trends of the critical E × B shear for edge harmonic oscillation onset in DIII-D quiescent H-mode plasmas

“…While H-mode exhibits energy confinement typically a factor of two better than that in low confinement (L-modes) plasmas, ELMs can be detrimental to plasma facing components, and represent a significant challenge for the design and operation of future fusion reactors [4]. As a result, interest has grown significantly in high confinement regimes with intrinsic ELM suppression [5].…”

Investigation of fast ion behavior using orbit following Monte–Carlo code in magnetic perturbed field in KSTAR

“…On the other hand, several methods to eliminate or mitigate the type-I ELM are proposed: a supersonic molecular beam injection, a pellet inection, an injection of RF wave, an utilization of MHD, an utilization of magnetic pertubation (These are comprehensively reviewed in Ref. [2]). To apply the method using magnetic pertubation to ITER, an ELM control coil system is planned to be installed in ITER.…”