DISTORTIONS IN THE CURRENT-VOLTAGE CHARACTERISTICS OF A ROCKET-BORNE LANGMUIR PROBE, CAUSED BY THE FORMATION OF PLASMA SHEATH: SOME NEW RESULTS

Formation of plasma sheath surrounding a sensor surface is known to distort the current-voltage characteristics of the sensor. Several sheath models that try to explain the experimental obseIvations exist. Rocketborne Langmuir probe measurements made from Natal, Brazil, on Oct 31, 1986, at 2259 hrs LST, provided some new results on the plasma sheath effect on the voltage-current characteristics of the conventional type of LP sensor. As the sensor potential increased from 0 to +4V the sensor current first increased and reached a maximum, as expected, but then showed an unexpected significant decrease before attaining the expected saturation level. A varying potential--drop across the plasma sheath, that develops surrounding the LP sensor seems to be responsible for these distortions in the LP characteristics.