PARAMETRIC DECAY IN THE EDGE PLASMA OF ASDEX DURING FAST WAVE HEATING IN THE ION CYCLOTRON FREQUENCY RANGE
Two types of parametric decay instabilities were observed in the scrape-off layer of ASDEX during hydrogen second harmonic heating, in the single- as well as in a two-ion-species plasma. The first type was identified as decay into an ion Bernstein wave and an ion cyclotron quasimode, and the second as decay into an ion Bernstein wave and a low frequency electron quasimode. The parametric decay processes are due to the high electric fields near the fast wave antennas. Theoretical growth rate calculations predict a threshold electric field which is in reasonable agreement with the values estimated from a full-wave code, modelling the relevant experiments. These parametric decay processes, as well as the harmonics of the generator frequency also seen in the scrape-off layer, provide a mechanism that might contribute to the observed direct energy deposition in the edge plasma and to ICRF-induced impurity production.
Bibliographic Reference: REPORT IPP III/129, 1988, AVAILABILITY: MAX-PLANCK-INSTITUT, MUENCHEN, D
Record Number: 1989126086900 / Last updated on: 1989-05-01
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