Low−temperature dielectric loss in polyethylene

A calorimetric technique was used to accurately determine the dielectric loss tangent of both additive−free and commerical grades of polyethylene at liquid−helium temperature. We found that the loss tangent of polyethylene often exhibits a broadened dielectric relaxation peak. Although this peak is centered in the kilohertz region, its existence increases the loss tangent at 60 Hz. Thus, the possibility of the elimination or reduction of this peak is important in evaluating the suitability of polyethylene as an insulator for a superconducting ac power transmission line. We have measured the intrinsic dielectric loss tangent of polyethylne and have found it to be ∼5×10−6. In addition, by systematically studying the influence of chemical additives on the dielectric loss, we have found the conditions necessary to obtain polyethylene exhibiting this low loss using present industrial production methods.