JET-P(91)63

Fast Wave Heating and Current Drive in JET: Present Results and Future Plans

A review is given of recent fast wave heating and current drive experiments on the JET tokamak. The heating studies encompass both minority cyclotron damping and direct electron absorption of the fast wave. In these experiments, a maximum power level of 22MW has been coupled to limiter plasmas. Bulk ion heating by minority ICRH has been demonstrated both in plasmas near the density limit and in pellet fueled H-mode discharges which reached a record thermal fusion product nd(o) teTi(0) = 7.8xl020m­3skeV. Electron heating by highly energetic minority tails appears to produce a saturation in the central electron temperature with increasing power per electron. Broadening of the heating profile by fast ion orbit effects could be the cause of this saturation. High quality H-modes have been produced with ICRF alone. With dipole phasing, te values up to 2.8 tgoldston have been obtained; with monopole phasing the enhancement factor over Goldston L-mode scaling is about 1.7. 3He minority ions have been accelerated up to lMeV tail temperature which is optimum for the 3He-D fusion reaction and have produced 140kW of non-thermal 3He-D fusion power. In high beta plasmas direct damping of the fast wave by combined TTMP and electron Landau damping has been observed. Current drive experiments include synergistic effects with LHCD, boostrap current with ICRF alone and minority ion current drive. The combination of LHCD and ICRH with monopole phasing produces an efficiency factor g = 0.4x1020m­2A/W due to damping of fast waves on the tail electrons generated by the LHCD. Up to 70% of the plasma current has been driven by the bootstrap current in lMA, bp ~ 2 plasmas. The broadening of the current profile stabilises the sawteeth. Phasing the ICRF antenna currents at 90o has a dramatic effect on sawteeth when the minority resonance layer is near the q = l surface. Normal sawteeth become monster sawteeth for +90o phase and are strongly destabilised for a phase of ­90o. An optimum power level is found for stability as expected from minority current drive theory.
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JETP91063 1.59 Mb