Characterization of Channel Structures Observed in the Radiation-Induced Dielectric Breakdown of Polymethyl Methacrylate for Space Applications

Dielectric breakdown due to solar radiation poses a significant problem for polymers in space. This type of component failure can be modeled in bulk dielectric materials, such as polymethyl methacrylate (PMMA). We irradiate the PMMA with an electron accelerator to accumulate space charge within the bulk, this we discharge by mechanical insult to force an electrical breakdown. This process forms permanent dendritic breakdown patterns, colloquially known as electrical trees. Here we study and categorize these trees using optical and electron microscopy by computer vision, and X-ray computed tomography.<br/> <br/>We investigate the various types of discharge. Other authors [1,2] have categorized the discharge channel structures into branch and bush types by their morphology. However, our analysis provides the first characterization of novel discharge channel types only observed in radiation-based dielectric breakdown [3]. We provide a structural description including a heuristic analysis and channel diameter measurements.<br/> <br/>We confirm the presence of branch and bush discharge structures and characterize a novel discharge structure and transition channel type, both of which suggest gaps in the present understanding of the physical processes at play.<br/> <br/>Acknowledgements:<br/>This work is supported by the Defense Advanced Research Projects Agency<br/> <br/>References:<br/>1. R. Schurch, S. M. Rowland, R. S. Bradley and P. J. Withers, in IEEE Transactions on Dielectrics and Electrical Insulation, vol. 21, no. 1, pp. 53-63, 2014, doi: 10.1109/TDEI.2013.003911.<br/>2. L. A. Dissado and J. C. Fothergill, in “Electrical Degradation and Breakdown in Polymers,” ed. Peter Peregrinus Ltd., (London, UK) 1992.<br/>3. K. Sturge, et al, in “Dynamics of High-Speed Electrical Tree Growth in Electron-Irradiated Polymethyl Methacrylate,” Science, (in press).