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In the initial phase of ITER H plasmas will be used in order to avoid activating the machine. The reference ICRF healing scenarios rely on minority species such as Helium (3He) or deuterium (D). These schemes’ distinctive feature comes from the presence of the fast magnetosonic wave ion-ion hybrid resonance/cut-off pair, between the antennas and the minority cyclotron layer. In order to document these unusual heating schemes, ICRF experiments were carried out recently on JET. First, the use of 3He ions in H plasmas was investigated with a sequence of discharges in which 5 MW of ICRF power was coupled to the plasma and the 3He concentration was varied from below 1% up to 10%. The inverted minority heating regime was observed at low concentrations (up to ∼2%). Energetic tails in the 3He distribution were observed with effective temperatures up to 300 keV and central electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and central electron temperature up to 8 keV. All these experiments systematically used power modulation techniques to assess the radial profiles of the wave absorption by the electrons. Secondly, experiments to study the ICRF heating of D minority ions in H were performed. This heating scheme proved much more difficult since modest quantities of C6+ impurity, which has the same Z/A ratio than the D minority ions, led us directly into the mode conversion regime. This effect preventing any absorption by D ions at minority cyclotron layer, could make the (D)H scenario not suitable for the non-active phase of ITER. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

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. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]