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Energy deposition characteristics in the ASDEX divertors have been analysed over a wide range of discharges and wall conditions during ohmically heated, additionally heated, or lower hybrid current drive experiments. Poloidally and toroidally resolved energy deposition patterns are particularly sensitive to changes in the edge safety factor, the type and power level of additional heating used, and the vertical position of the plasma. Poloidal in-out asymmetries, which typically favour the low-field side by a factor of 2.5 in ohmic discharges, commonly range between a factor of 2.5 and 4.5 in additionally heated experiments and in extreme cases can be as large as a factor of 5.6. At the same time, toroidal asymmetries on individual target rings are found to range between a factor of 1.4 and 3.8 in typical ICRH and NBI cases with extreme LHCD cases of 4.3. A model, proposed to explain the cause of discharge asymmetries, is compared with the experimental observations. Under some conditions, for example during LHCD experiments, the model is in good agreement with the data. In other situations it appears that effects not yet incorporated in the model are needed to explain the data. A method is proposed for suppressing discharge asymmetries which may generally improve the divertor performance as well.

Additional information

Authors: EVANS T E, General Atomics, San Diego (US);ASDEX TEAM, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP III/154 EN (1991)
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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