Bonn 2000 – wissenschaftliches Programm
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P: Plasmaphysik
P 14: Magnetischer Einschluss III
P 14.5: Vortrag
Freitag, 7. April 2000, 12:30–12:45, HS V
Pellet refueling in H-mode plasmas: a comparison of ASDEX Upgrade und JET — •P.T. Lang1, O. Gruber1, L. Horton2, T.T.C. Jones2, A. Lorenz1, M. Maraschek1, V. Mertens1, J. Neuhauser1, G. Saibene2, ASDEX Upgrade1, and JET Teams2 — 1Max Planck Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, D-85748 Garching — 2JET Joint Undertaking, Abingdon, Oxfordshire, United Kingdom
Injection of cryogenic hydrogen isotope pellets from the magnetic high field side has been shown to bear the possibility to overcome the H-mode density limit in tokamaks. Using this technique both, in ASDEX Upgrade and JET, operation at densities far beyond the Greenwald density was achieved while maintaining H-mode conditions. However, the plasma energy confinement degrades while the pellet train is injected, but can recover after the sequence faster than the pellet induced density surplus decays. Further enhancement of the performance can be achieved by optimization of the pellet fueling cycle, minimizing particle and power losses following pellet injection. These losses were associated with bursts of ELMs triggered by the injection. Showing similar behaviour at ASDEX Upgrade and JET, the bursts are composed of typically 3-7 single ELMs expelling thermalized pellet deposited particles from the plasma column. However, ELM bursts in JET can last significantely longer (100 ms compared to 10 ms) and cause stronger degradation of the initial plasma energy content (0.5 times compared to 0.1 times) than at ASDEX Upgrade.