ICRF Launcher for Reduction of Impurity Production

An ion cyclotron range of frequencies (ICRF) launcher which minimizes the RF field at the resonance surface near the plasma edge to reduce impurity production is proposed. The launcher consists of a main antenna and short compensating antennas. The compensating current needed for minimizing the RF field is calculated. It is shown that the power required for the compensating antenna is reasonable. The current requirement is relatively insensitive to changing resonance location and wavenumber spectrum.