Heating (3He)-H JET Plasmas with Multiple Mode Conversion Layers

The constructive interference effect described by Fuchs et al. shows that the mode conversion and thereby the overall heating efficiency can be enhanced significantly when an integer number of fast wave wavelengths can be folded in between the (high field side) fast wave cutoff and the ion-ion hybrid layer(s) at which the ion Bernstein or ion cyclotron waves are excited. This effect was already experimentally identified in (3He)-D plasmas and was recently tested in (3He)-H JET plasmas. The latter is a so-called 'inverted' scenario which differs significantly from the (3He)-D scenarios since the mode-conversion layer is positioned between the low field side edge of the plasma and the ion-cyclotron layer of the minority 3He ions (whereas the order in which an incoming wave encounters these layers is inverted in a 'regular' scenario), and because much lower 3He concentrations are needed to achieve the mode conversion heating regime. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the 3He concentration were observed in the JET experiments. The unwanted presence of both 4He and D in the discharges gave rise to 2 mode conversion layers rather than a single one. This together with the fact that the location of the high field side fast wave cutoff is a sensitive function of the parallel wave number and that one of the confluences' locations critically depends on the'3He concentration makes the interpretation of the results more complex but also more interesting:
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