Boundary probe for measurement of current density and electric-field strength—with special reference to ionised gases

Abstract

An active probe is described that is suitable for measurement of current density J and electric-field strength E over an electrode boundary. It is capable of high mechanical resolution, since spatial accuracy of 0.5 mm is readily obtainable. Calibration of the probe is in terms of its mechanical dimensions, so that J may be determined to within ±1%, and E to within ±5%. The measurement of E is dependent on those situations where the motion of carriers is due to electrical drift; so that, in gases, the mean free path of ions should be less than a probe diameter. No such restriction applies to J. The probe has an interesting characteristic that is shown to have considerable generality in ionised air at s.t.p. It may prove to possess much wider generality. The method is presented and verified for static fields. Gaseous discharges and electrolytes may be usefully examined, and their conductivity measured directly.