On the mechanism of electric breakdown under low-pressure discharge in helium

It us shown that the left branch of the Paschen curve is determined by the gas phase breakdown, which is caused by the electron avalanche at pD ≥ (pD)e and by the gas ionization by fast positive ions at pD < (pD)e. The (pD)e threshold value is evaluated, and it is established that the E/p ratio is the main parameter determining the gas breakdown.