Suppression of large edge localized modes with edge resonant magnetic fields in high confinement DIII-D plasmas

Evans, T. E.; Rudakov, D. L.; Rhodes, T. L.; Fenstermacher, M. E.; Groth, M.; Wang, G.; West, W. P.; Lasnier, C. J.; Groebner, R. J.; Osborne, T. H.; Pretty, D. G.; Doyle, E. J.; Schaffer, M. J.; Reimerdes, H.; Ohyabu, N.; Masuzaki, S.; Zeng, L.; La Haye, R. J.; Jackson, G. L.; Wade, M. R.; Watkins, J. G.; Finken, K. H.; Bécoulet, M.; Harris, J. H.; Boedo, J. A.; Thomas, P. R.; Moyer, R. A.

doi:10.1088/0029-5515/45/7/007

Journal Article

Suppression of large edge localized modes with edge resonant magnetic fields in high confinement DIII-D plasmas

Evans, T. E. ; Moyer, R. A. ; Watkins, J. G. ; Osborne, T. H. ; Thomas, P. R. ; Bécoulet, M. ; Boedo, J. A. ; Doyle, E. J. ; Fenstermacher, M. E. ; Finken, K. H.FZJ* ; Groebner, R. J. ; Groth, M. ; Harris, J. H. ; Jackson, G. L. ; La Haye, R. J. ; Lasnier, C. J. ; Masuzaki, S. ; Ohyabu, N. ; Pretty, D. G. ; Reimerdes, H. ; Rhodes, T. L. ; Rudakov, D. L. ; Schaffer, M. J. ; Wade, M. R. ; Wang, G. ; West, W. P. ; Zeng, L.

2005
IAEA Vienna

Nuclear fusion 45, 595 - 607 (2005) [10.1088/0029-5515/45/7/007]

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Please use a persistent id in citations: http://hdl.handle.net/2128/1898 doi:10.1088/0029-5515/45/7/007

Abstract: Large sub-millisecond heat pulses due to Type-I edge localized modes (ELMs) have been eliminated reproducibly in DIII-D for periods approaching nine energy confinement times (tau(E)) with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-l ELM impulses during a coil pulse is less than 0.4% of plasma current. Based on magnetic field line modelling, the perturbation fields resonate with plasma flux surfaces across most of the pedestal region (0.9 <= psi(N) <= 1.0) when q(95) = 3.7 +/- 0.2, creating small remnant magnetic islands surrounded by weakly stochastic field lines. The stored energy, beta(N), H-mode quality factor and global energy confinement time are unaltered by the magnetic perturbation. Although some isolated ELMs occur during the coil pulse, long periods free of large Type-l ELMs (Delta t > 4-6 tau(E)) have been reproduced numerous times, on multiple experimental run days in high and intermediate triangularity plasmas, including cases matching the baseline ITER scenario 2 flux surface shape. In low triangularity, lower single null plasmas, with collisionalities near that expected in ITER, Type-l ELMs are replaced by small amplitude, high frequency Type-II-like ELMs and are often accompanied by one or more ELM-free periods approaching 1-2 tau(E). Large Type-I ELM impulses represent a severe constraint on the survivability of the divertor target plates in future burning plasma devices. Results presented in this paper demonstrate that non-axisymmetric edge magnetic perturbations provide a very attractive development path for active ELM control in future tokamaks such as ITER.

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