Fields of short radio-frequency probes in a magnetized plasma

The diagnostics of a magnetized plasma can be done by measuring the spacings of the interference structure in the angular distribution of the field of a properly excited probe in the plasma. In this paper the effect of probe dimensions on the interference structure is investigated. The sheath around the probe is found to have profound effects on the angular distribution of both the phase and the amplitude of the filed of the probe. This investigation reveals that only thin electric dipole of half-length less than 30 Debye lengths or so is useful for the plasma diagnostics