Frequency dependence of helicon wave plasmas near lower hybrid resonance frequency

The frequency dependence of helicon wave plasmas has been studied at 1–25 MHz of rf power, and at magnetic fields of 200–1150 G using various gases. Maxima in the electron density occur for particular frequencies at each magnetic field. These optimum frequencies are propor-tional to magnetic field strength and inversely proportional to the discharge gas mass. The exist-ence of optimum frequencies in each magnetic field and gas mass indicates the possibility of lower hybridresonance heating effect. The experimental optimum frequencies are slightly lower than the theoretical lower hybrid resonance frequencies. The difference between the two frequencies can be explained by the Doppler shift effect.