Abstract
Experiments have been carried out on the JET tokamak to investigate differences between multiple and single frequency ICRH operation with ICRH power in the range of 3 to 8 MW using H and 3He minority heating. High‐energy neutral particle analysis and gamma‐ray emission tomography are used to measure fast ions, including their radial localisation. For 3 MW of 3He minority heating, the fast 3He ion profile is broader according to the gamma emission data and the fast ion tail temperature Ttail and energy content Wfast are lower with polychromatic ICRH than monochromatic ICRH. Polychromatic ICRH has the advantage of producing smaller‐amplitude and shorter‐period sawteeth, consistent with a lower fast ion pressure inside q = 1, and higher Ti/Te ratios (i.e. similar Ti at lower Te). At high powers with resonances in the centre and/or on the low field side, the data indicates a larger fraction of trapped ions and a lower Ttail for polychromatic ICRH. Experimental results are compared with theoretical predictions.
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