TSDC spectra of polyimide aged in a simulated space environment

Thermally stimulated discharge current (TSDC) techniques have been used to examine the behaviour of polyimide insulation that has been subjected to an aging procedure comprising gamma irradiation under vacuum to a dose of 500 kGy followed by thermal treatment under vacuum. The thermal treatment consisted of two regimes, one cycling between room temperature and 420 K with a 24 hour period and the other constant at a temperature of 420 K. Results are presented for samples which have been subjected to these conditions for periods between 6 and 24 months and are compared with those obtained from pristine material. It is observed that marked changes in the TSDC characteristics are brought about by the different aging procedures