The development of the discharge plasma in a hydrogen spark at small pd values

The development of plasma parameters in a spark discharge is studied using spectroscopic techniques. It is observed that a transition from a molecular glow discharge to a fully ionized arc channel plasma takes place in the discharge column after initiation of a radial shock wave. Finally the transition from a γion process to a cathode spot mechanism initiates an axial shock wave of Mach number M =1·38 moving through the fully ionized channel from cathode towards anode.