Effect of Fluence on Electron Deposited Charge Distributions in Polytetrafluoroethylene

Charge embedded in highly-insulating dielectric polymers such as polytetrafluoroethylene (PTFE) are important in many applications from high voltage DC power transmission to spacecraft charging. Fluence of the incident electrons can change the resulting charge distribution in potentially unexpected ways. While the magnitude of the measured charge distribution will obviously increase with increased fluence, the shape of the distribution may also change. This can be due to effects such as radiation induced conductivity, damage to material, and interactions between embedded and incident electrons. To test the effects of fluence on charge deposition in PTFE, several samples of 150 µm thick PTFE were irradiated with varying fluence. This was achieved with an 80 keV monoenergetic electron beam with flux ranging from 0.3-1 nA/cm² flux for 2-8 minutes resulting in fluence from 36-480 nC/cm². The embedded charge distributions were then measured in ambient conditions with a pulsed electroacoustic (PEA) system. The measurements were then compared to show the differences in the resulting charge distributions. The effects of varying fluence include changes in the shape, magnitude, position, and introduction of positive charge in the measured distributions.