Edge localized mode control with an edge resonant magnetic perturbation

Date

2005-04-28

Authors

Moyer, R. A
Evans, T. E
Osborne, T. H
Thomas, P. R
Becoulet, M.
Harris, J.
Finken, K.-H
Boedo, J. A
Doyle, E. J
Fenstermacher, M. E

Journal Title

Journal ISSN

Volume Title

Publisher

American Institute of Physics

Abstract

A low amplitude (δbr∕BT=1 part in 5000) edge resonantmagnetic field perturbation with toroidalmode number n=3 and poloidal mode numbers between 8 and 15 has been used to suppress most large type I edge localized modes(ELMs) without degrading core plasma confinement. ELMs have been suppressed for periods of up to 8.6 energy confinement times when the edge safety factor q95 is between 3.5 and 4. The large ELMs are replaced by packets of events (possibly type II ELMs) with small amplitude, narrow radial extent, and a higher level of magnetic field and density fluctuations, creating a duty cycle with long “active” intervals of high transport and short “quiet” intervals of low transport. The increased transport associated with these events is less impulsive and slows the recovery of the pedestal profiles to the values reached just before the large ELMs without the n=3 perturbation. Changing the toroidal phase of the perturbation by 60° with respect to the best ELM suppression case reduces the ELM amplitude and frequency by factors of 2–3 in the divertor, produces a more stochastic response in the H-mode pedestal profiles, and displays similar increases in small scale events, although significant numbers of large ELMs survive. In contrast to the best ELM suppression case where the type I ELMs are also suppressed on the outboard midplane, the midplane recycling increases until individual ELMs are no longer discernable. The ELM response depends on the toroidal phase of the applied perturbation because intrinsic error fields make the target plasma nonaxisymmetric, and suggests that at least some of the variation in ELM behavior in a single device or among different devices is due to differences in the intrinsic error fields in these devices. These results indicate that ELMs can be suppressed by small edge resonantmagnetic field perturbations. Extrapolation to next-step burning plasma devices will require extending the regime of operation to lower collisionality and understanding the physical mechanism responsible for the ELM suppression.

Description

Keywords

Keywords: Density fluctuation; Edge localized mode (ELM); Fusion plasmas; Particle impulse; Error analysis; Extrapolation; Magnetohydrodynamics; Perturbation techniques; Plasma confinement; Plasma density; Plasma devices; Random processes; Safety factor; Transport

Citation

Source

Physics of Plasmas

Type

Journal article

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