Ion Cyclotron Heating
Radiofrequency (RF) antenna systems that excite compressional Alfven or "fast" waves, typically operating in the frequency range of 10-120 MHz, are used for both cyclotron magnetic resonance heating of ions and non-resonant heating of electrons. In addition to heating plasmas to the high internal temperatures needed to initiate fusion reactions, RF waves can be used to drive plasma currents, tailor internal pressure profiles, improve energy confinement, and stabilize plasmas. RF systems on present major U.S. experiments are capable of supplying 3-6 MW of power to their plasmas; future reactors such as ITER may need an order of magnitude more power.
There are technology challenges to reliable operation of RF wave launchers with hundreds of amps of current flowing at tens of thousands of volts a few cm from a hot, electrically conducting plasma. Deleterious interactions between the plasma and antenna must be minimized, large electromagnetic forces operating on the antenna structure during plasma disruptions must be withstood, techniques to maintain power delivery to the plasma's rapidly varying electrical load must be developed, and components compatible with the high flux neutron environment of future reactors must be deployed. Although antenna component development and qualification on dedicated test facilities is followed as much as possible, the intimate close coupling between the antenna and plasma ultimately demands that final technology assessment and improvement be carried out on operating plasma experiments. We have designed, fabricated, and operated multimegawatt RF antennas on major U.S. and international experiments.