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High-efficiency tokamak plasma refuelling with cryogenic pellets injected from the magnetic high-field side is demonstrated. In this novel injection scheme, a blower gun was used to inject deuterium pellets (up to 130 m/s at up to 17 Hz) through a guiding tube from the magnetic high-field side of the ASDEX Upgrade divertor tokamak. In contrast to standard low-field side injection, these experiments, performed in ELMy H-mode discharges, showed almost no rapid loss of particles and energy. Consequently, under identical starting conditions, the plasma refuelling efficiency was up to 4 times as large as for the standard injection scheme with virtually unchanged energy confinement. It is suggested that the large, nearly instantaneous particle losses in the standard scheme are mainly due to the toroidal drift force pushing deposited material towards the low-field side plasma edge and eventually out of the plasma column in the case of shallow pellet penetration. In contrast, for shallow high-field side injection, this drift is directed towards the plasma core and therefore enhances bulk fuelling. In this new scheme, a further benefit is derived from enhanced pellet shielding, and hence deeper pellet penetration, caused by the ablated material drifting in the same direction as the solid pellet in the case of high-field side injection.

Additional information

Authors: LANG P T ET AL, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/304 EN (1996) 24pp.
Availability: Available from the Max-Planck-Institut für Plasmaphysik, 85748 Garching bei München (DE)
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