ELM-related fluctuations in PBX-M H-modes

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Abstract
Edge Localized Modes have been studied in PBX-M discharges with high data sampling rate magnetic diagnostics with good spatial coverage. High frequency (>or=250 kHz) activity appears prior to the increase in the Dalpha emission. While this high frequency activity is global, with high coherence for all coils both on the inside and outside midplane, there is no identifiable mode structure. A very intense outward ballooning feature appears simultaneously with the increase in the Dalpha emission, and lasts for about 5 msec. The toroidal mode structure of this feature is clearly identifiable, consisting of a series of toroidal harmonics from n=3 to 8, at frequencies given by fn=f0+n Delta f, where Delta f=20-30 kHz and f0=30-50 kHz. This feature may be caused by the kinetic ballooning mode.