Measurement and Modeling of Time Domain Dielectric Response of Insulating Materials at Cryogenic Temperature

The design and fabrication of a new experimental setup for time-domain dielectric response measurements of cryogenic electrical insulation materials for superconducting devices are described. The polarization current responses of polypropylene laminated paper (PPLP), polyimide (PI), and polyethylene (PE) at 77 K are reported. Using the extended Debye model, the dielectric response function, polarization time constant and DC electrical conductivity of PPLP, PI, and PE are derived at 77 K. The differences in the dielectric response of the materials between room temperature and 77 K and liquid nitrogen and pressurized helium gas, both at 77 K, are discussed. The 77 K polarization time constant is much larger than the corresponding room temperature value due to the lower DC electrical conductivity at 77 K. The polarization time constant of an insulating material has a marginal sensitivity to the cryogenic medium. The fundamental data and its relevance in designing electric insulation systems of cryogenic DC power system components such as superconducting devices are presented.