Constriction of a high-pressure glow discharge in hydrogen

An image converter was used as a fast streak camera to study the glow-to-arc transition in a uniform field hydrogen discharge gap (160-460 Torr pressure). The maximum discharge current was about 850 A. For the first 20-30 shots or so, with stainless steel electrodes, the constriction of the glow always started at the cathode irrespective of pressure and overvoltage. When the electrodes became conditioned, i.e. after about 100 shots, the constriction was initiated at the anode for overvoltages up to a critical value depending on the gas pressure. Above the critical overvoltage the constriction began at the cathode, and at the critical overvoltage the constriction was initiated in mid-gap and propagated in both directions.