Instrument for Electrical Evaluation of High-Voltage Insulation Exposed to Ionospheric Plasma

The importance of dielectrics for high-voltage applications in space arises from a growing demand for large amounts of power, presently at up to about 20 kV. The most difficult insulation problem exists when the dielectric is exposed to the relatively dense ionospheric plasma. The dielectric phenomena requiring investigation are surface and volume conduction currents, photoconduction currents, nondestructive breakdowns, destructive breakdowns, and pinhole currents. There are several unusual requirements for a suitable space-dielectric evaluation instrument. Only one surface of the test dielectric is to be in contact with a solid conducting electrode. The other surface of the dielectric is completely exposed to the vacuum and unaltered (no applied conducting surface coating). Means must be provided for depositing electrical charges on the exposed surface, with negligible impact energies, to produce the desired voltage across the test dielectric. The exposed dielectric surface potential must be measured continuously. A suitable instrument has been devised and used. In it the dielectric is charged by a positive ion or an electron beam of known energy and current density.