Modelling of Effects of Ripple-Induced Thermal Ion Losses on JET and JT-60U H-mode Plasmas

The discreteness of the toroidal magnetic field coil configuration in tokamaks shows up as ripple in the toroidal magnetic field, which results in ripple losses of both thermal and fast ions. In the H-mode, which is characterised by the formation of an edge transport barrier with a reduction of transport to a low ion neo-classical level, the influence of additional ion thermal transport due to ripple losses at the edge may be very discernible. Experimental observations seem to go in line with this assumption. In a recent series of dimensionless pedestal identity experiments at JET and JT-60U, a noticeable difference in pedestal performance and ELM frequency was found between the two machines despite a good match in the main dimensionless plasma parameters . The stronger toroidal magnetic field ripple at JT-60U has been proposed as a possible reason for these differences.
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