Breakdown strength of PPLP and kapton in liquid hydrogen and comparison with liquid nitrogen

Electricity transmission with superconducting cables uses various cooling media. Liquid hydrogen (LH2) is well suited for magnesium diboride (MgB2), but the breakdown strength of LH2-impregnated insulation has not been tested yet. In this letter, polypropylene laminated paper (PPLP) and polyimide (Kapton) insulation structures are tested in the same conditions in LH2 and LN2 (liquid nitrogen). The results show that Kapton presents a similar behavior for both cooling media whereas PPLP exhibits a lower shape parameter, i.e. a broader breakdown event scattering, in LH2 than in LN2 though scale parameters, i.e. breakdown strength at 63% cumulative probability, are similar.