The development of the apparatus to measure electric field in the presence of ionisation

Abstract

An Introductory survey of investigations in the Earth’s Atmosphere and beyond, gives evidence from phenomena such as Aurora, Dynamo Theory, and Ionospheric irregularities, for the desirability of detecting and measuring electrostatic fields in these regions, The electrical phenomena associated with isolated conductors in ionised regions are discussed, and the differences and similarities between electrical measurements in laboratory plasmas and extraterrestrial plasmas are pointed out. Estimates for the electric fields and currents interacting with an exposed conductor isolated from the main body of a rocket or satellite in the extra terrestrial plasma are obtained. Considering these estimates, a theory for a device to detect such fields and currents is obtained. This device is in effect, two field mills each having the layout first put forward by Malan and Schonland (1950), rotating about the same axis but working at two different frequencies. This allows two equations to be set up which may be solved for applied field or for applied current. The means for testing and calibrating such an instrument in the laboratory are discussed and the test chamber constructed for the preliminary model is described, and an idea of the results obtained is given. The construction of a mill for flight in an aerobe-Hi rocket, and of apparatus for its accurate calibration is described, and results given for the field, and current sensitivities of both ‘halves’ of the mill. The field sensitivities (9.0 x 10(^-6) and 6 x 10(^-6). Volts/v/m. approx) are as much as 85% of the outputs predicted by theory, but the current sensitivities are best expressed by powers, less than unity, of the applied current, giving for total currents greater than 10(^-9)amps; (V – a) = (10(^10)I)(^b) where V is the mill output, I is the total applied current, a. is the mill output when I <10(^-10)amps, the lowest sensitivity of the current measuring element in the calibration circuit (a. is negligibly different from zero output) and b is the slope of V against I plotted on log. Log. axes. The interpretation of the ‘field and current’ total mill output signals is discussed, and suggestions made to explain departures from theoretical predictions.