Abstract
Significant levels of parametric decay activity and correlated edge ion heating were observed during injection of high power ion Bernstein waves (IBWs) in DIII-D. Both minority hydrogen ions and majority deuterium ions showed the formation of a high energy perpendicular tail; no parallel heating was observed. The edge ion heating and the parametric decay activity were both strongest when an ion cyclotron harmonic was present at the plasma edge. Ion tail formation had a power threshold of several hundred kilowatts, above which the tail size increased with antenna power; a comparable power threshold for parametric decay instability (PDI) was observed. Both the PDI and the associated edge deuterium heating were found to be sensitive to the hydrogen-to-deuterium ratio
Highlights
The application of externally launched ion Bernstein waves (IBW) to heat a tokamak plasma was proposed [l,23 in 1979
IBW heating combines the advantages of lower hybrid heating and fast wave heating in the ion cyclotron range of frequencies (ICRF)
In some recent fast wave heating experiments, parametric decay instabilities (PDI) have been observed [3,4].Though the presence of parametric decay processes at some low level does not necessarily constitute a problem for an RF heating scheme, in at least one large tokamak, JT-60,the PDI has been found to be well correlated with enhanced impurity production [5,6]
Summary
The application of externally launched ion Bernstein waves (IBW) to heat a tokamak plasma was proposed [l,23 in 1979. The processes shown in Fig. 1include the following: (i) decay into an IBW and an ion cyclotron quasimode (ICQ), the latter having frequencies which correspond to the deuterium, and/or hydrogen ion cyclotron frequency; (ii) decay into an LBW and an electron Landau damped quasi-mode (ELDQ); (iii) resonant decay into two ion Bernstein waves. All of these processes have been observed in the DIII-D IBW experiments.
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