Characteristics of the cyclotron harmonic resonances found by impedance probe experiments in a laboratory plasma

The RF impedance of an antenna in a thermal magnetized plasma shows resonances associated with the electron cyclotron harmonic frequency. To understand the impedance probe observations in the thermal anisotropic plasma, characteristics of the cyclotron harmonic resonances have been examined. We verified that both the series and parallel types of the resonances occurred in a laboratory experiment. The resonance effect became clear when the static magnetic field was nearly parallel to the cylindrical probe axis. In this case the cyclotron harmonic resonances would act to smear the upper hybrid resonance, the measurement of which is essential to know the electron density. It was also found that the 2nd order of the cyclotron harmonic series resonance sometimes became much clearer than the plasma sheath resonance which is a main series resonance in the cold plasma. The ion sheath surrounding the probe probably played a significant role to produce such unique resonance characteristics in the thermal plasma. (author)