Lichtenberg Figures In Liquid And Supercritical Helium

Photographic Lichtenberg figures were taken in cryogenic (4.2 – 5.9 K) high density helium including liquid and supercritical helium by applying lightning impulse voltages. The Lichtenberg figures in the cryogenic high density helium had a larger extent with negative polarity than with positive polarity. This polarity effect is consistent with the breakdown voltage in cryogenic high density helium in a non-uniform field, whereas common insulating fluids have the opposite polarity effect in both the Lichtenberg figure and breakdown voltage. This result is accounted for by the depletion of free electrons in cryogenic high density helium.