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This work comprises results obtained using the new centrifuge injection system for the two first years of pellet injection experiments at Asdex Upgrade. The main aim of the pellet injection investigation is to develop scenarios allowing for a more flexible plasma density control by means of injection of cryogenic solid hydrogen pellets. While the injection of pellets during ohmic discharges was found to be most efficient and also improves the plasma performance, increasing the auxiliary heating power causes a detoriation of the pellet fuelling efficiency. A further strong reduction of the pellet fuelling efficiency by an additional process was observed for the more reactor relevant conditions of shallow particle deposition during H-mode phases. With injection during type I ELMy H-mode phases, each pellet was found to trigger the release of an ELM and therefore cause particle losses mainly from the edge region. In the type I ELMy H-mode, only sufficient pellet penetration allowed noticeable, persistent particle depositon in the plasma by the pellets. Applying adequate pellet injection conditions and favourable scenarios using combined pellet and gas puff refuelling, significant density ramp-up, to densities exceeding the empirical Greenwald limit by up to a factor of two, was achieved even for strongly heated H-mode plasmas.

Additional information

Authors: LANG P T ET AL, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/296 EN (1996) 36pp.
Availability: Available from the Max-Planck-Institut für Plasmaphysik, 85748 Garching bei München (DE)
Record Number: 199610710 / Last updated on: 1996-06-21
Original language: en
Available languages: en