The Characteristics of a Space-Vehicle-Borne Charged Particle Sensor

摘要

An expression is developed for the current flow to n spheres with known potential differences between them in a drifting Maxwellian plasma. By equating this to zero and solving the resulting equation numerically, one obtains the potential of the spheres relative to the plasma. A charged particle sensor mounted on a space vehicle is then investigated, represented by a two-sphere system. The current-voltage characteristic produced by sweeping the potential difference between the two spheres is derived and shown to be distorted by the variation of the vehicle potential. A method of correction, that is, by the introduction of a third sphere, is described. The effects of area ratio, temperature, and drift velocity are investigated. An attempt is made to use this method to throw some light on the case where the vehicle is cylindrical. The added complications owing to the attitude sensitivity of the system as soon as any electrode becomes nonspherical are immediately apparent. Finally, the implications of the theory in temperature determination from the sensor characteristic are discussed. (Author)