Results of RF Heating on JET and Future Prospects
Ion Cyclotron Resonance Heating (ICRH) has been applied to various JET plasmas with net coupled powers reaching 7MW for several seconds. Conditioningwith helium discharges is shown to be effective in controlling the density and in reducing the total radiated power to about 25% of the input power. On axis heating invariably results in long sawteeth of large amplitude. In most high power cases, a sudden bifurcation to monster sawteeth as long as 1.6s is observed. The monster sawtooth is accompanied by an improvement in energy confinement time (+20%) and by an increase in density. Central electron and ion temperatures of 7 and 5.5keV respectively have been achieved with 6.5MW of ICRF power. The heating rate is reduced with off-axis heating in agreement with diffusive heat transport models. The future RF programme on JET includes upgrading the ICRF power to 20MW and the development of current drive methods using a phased ICRF array of 8 antennae and later on a Lower Hybrid Current Drive system at 3.7GHz with a 10MW launcher.