Plasma heating experiments have been carried out at twice the ion cyclotron frequency in a single quadrupole minimum-|B| end plug mirror of the Phaedrus tandem mirror. The application of 23 kW of RF power increased the average ion energy by a factor of five and doubled the electron temperature. The ion heating was characterized by strong tail heating and a concentration of the hot-ion population between the two resonance zones of the mirror. Best ion heating was observed with the resonance zone located 11.5 ± 2 cm from the midplane, this being approximately halfway between the antenna and the midplane. Electron heating was observed even under conditions where little ion heating was seen.
On the role of electron energy distribution function in double frequency heating of electron cyclotron resonance ion source plasmas