Breakdown characteristics of He gas at cryogenic temperature and low pressure

The breakdown of He between plane electrodes was investigated under conditions similar to those of the operation of superconducting magnets at room temperature and 4 K. It was found that the breakdown voltage in the Paschen minimum was higher than expected at room temperature, which was explained by the presence of impurity. An additional effect observed, especially at low pressures, is that the measured pressure in the vacuum vessel does not seem to agree with the pressure of the electrode gap. Furthermore a helium leak of 1 Pa 1/s was introduced between the electrodes. No measurable influence of this leak was found within the measuring accuracy at low temperatures