Experiments in DIII-D toward achieving rapid shutdown with runaway electron suppression

• Published in: Physics of plasmas 2010-05, Vol.17 (5)
• Main Authors: Hollmann, E. M., James, A. N., Yu, J. H., Izzo, V. A., Commaux, N., Jernigan, T. C., Baylor, L. R., Eidietis, N. W., Parks, P. B., Wesley, J. C., Brooks, N. H., Jackson, G. L., Zeeland, M. A. van, Wu, W., Evans, T. E., Humphreys, D. A., Strait, E. J., Austin, M. E.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CLOSED PLASMA DEVICES; DOUBLET-3 DEVICE; ELECTRON DENSITY; ELECTRONS; ELEMENTARY PARTICLES; FERMIONS; IMPURITIES; INHIBITION; LEPTONS; PELLET INJECTION; PLASMA IMPURITIES; RUNAWAY ELECTRONS; SHUTDOWN; THERMONUCLEAR DEVICES; TOKAMAK DEVICES
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.3309426

Experiments have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] toward understanding runaway electron formation and amplification during rapid discharge shutdown, as well as toward achieving complete collisional suppression of these runaway electrons via massive delivery of impurities. Runaway acceleration and amplification appear to be well explained using the zero-dimensional (0D) current quench toroidal electric field. 0D or even one-dimensional modeling using a Dreicer seed term, however, appears to be too small to explain the initial runaway seed formation. Up to 15% of the line-average electron density required for complete runaway suppression has been achieved in the middle of the current quench using optimized massive gas injection with multiple small gas valves firing simultaneously. The novel rapid shutdown techniques of massive shattered pellet injection and shell pellet injection have been demonstrated for the first time. Experiments using external magnetic perturbations to deconfine runaways have shown promising preliminary results.