Radio-frequency impedance probes

The behaviour of radio-frequency probes in a magneto-ionic environment is important in connection with their use for measurement of ionospheric parameters and in the design of aerials for rockets and satellites. The present theoretical treatment of radio-frequency probes is outlined and applied to systems of differing configurations. The difficulties which arise when the wave frequency is not large compared with the gyro-magnetic and plasma frequencies are discussed, including especially the origin of the resistive term which can be finite, even in a collisionless plasma. Some attention is given to the effect of the plasma sheath which may surround a probe system. A number of practical systems are described and the problems in interpreting impedance measurements are considered.