Analysis of pre-breakdown pulse activity of multi-stressed Kapton film

Kapton (polyimide) is a material that is used widely in applications in outer space and the present work describes a study of pre-breakdown electrical pulse activity under direct stress after the material has experienced an aging regime comprising different combinations of gamma radiation, vacuum and temperature, these being some of the principal environmental stimuli to be experienced in space. Following aging for periods between 6 and 18 months, test specimens were transferred to a space simulation chamber (SSC) which provides for an environment that can encompass high vacuum (10^-6 mbar), temperature within the range 80-470 K and ⁶⁰Co γ-radiation at low dose rates of several mGy/h. Here measurements of pre-breakdown pulses were made in real-time whilst experiencing different combinations of the above stimuli within the SSC. It was found that for a given applied field, the pulse activity was thermally activated in that it increased with increasing sample temperature. Also for a given radiation dose, samples subjected to long periods of thermal treatment generated more pulses than material which had experienced shorter ones. In addition, for a given aging period, thermal cycling results in a greater pulse activity than does constant temperature. These processes involve radiation-induced charge trapping and thermal detrapping and have implications for the long-term deployment of insulation in space