Shock front formation at vacuum arc anodes

Abstract

A vacuum arc plasma jet between copper electrodes is considered as a supersonic hydrodynamic jet (the primary plasma jet) that bombards the anode and sputters and/or reflects ions (secondary plasma). An initial primary ion jet velocity of v0=1.5×104 m/s is assumed. The time-dependent interaction between primary and secondary ions is considered for primary ion concentrations of n0=1018 and 1019 m−3 and for a Cu-Cu self-sputtering yield coefficient of β=0.2. It is found by numerical calculation that the primary jet is decelerated by the collisions with the secondary ions. In the case where the mean free path in the primary plasma is much less than the interelectrode gap (l11≪L) and the mean free path for the primary-secondary ion collision is much more than the interelectrode gap (l12≫L), the primary jet decelerates, but initially remains supersonic, while at a later time the deceleration is to a subsonic value, and a shock front appears. For a primary ion concentration of n0=1018 m−3 and an initial secondary ion velocity ≈0.1×v0, a shock front appears at time t≈245×L/v0 while for n0=1019 m−3, at t≈135×L/v0.

Anode jet in a high-current vacuum arc

“…Then, the collision of the fluxes with subsequent slowing down may lead to the formation of an ionization-recombi nation front (IRF), in which the resonance charge exchange in ion-atom collisions is the main ioniza tion mechanism of the anode flux neutral component. With regard to the results reported in [11], this exchange may cause the formation of a sheath of excited atoms with an ion halo around it. The structure of such a front is shown in Fig.…”

“…In this case, the cathode plasma flux may slow down to a stop. In contrast to [11], where both fluxes were considered as a highly ionized plasma, we assume that the anode plasma is weakly ionized. Then, the collision of the fluxes with subsequent slowing down may lead to the formation of an ionization-recombi nation front (IRF), in which the resonance charge exchange in ion-atom collisions is the main ioniza tion mechanism of the anode flux neutral component.…”

“…These find ings can be discussed using the model described in [11]. According to [11], collisions between the cathode plasma propagating with a velocity of 10 6 cm/s and the anode plasma propagating with a lower velocity may form a stable wavefront in the arc gap. In this case, the cathode plasma flux may slow down to a stop.…”

Sub- and supersonic expansion of an arc channel in liquid

“…A theory of the discharge and the hydrodynamic waves which it produces in the surrounding liquid would be of value not only in understanding these phenomena but also in optimizing applications. Gidalevich et al [8,9] considered shock wave propagation in water during thermal expansion of the discharge channel. However, the subsonic stage of the channel expansion and the transonic expansion regime were not considered to date.…”

“…However, the subsonic stage of the channel expansion and the transonic expansion regime were not considered to date. The objective of this work was to develop a model of the subsonic discharge channel expansion and to connect it with the supersonic solution developed earlier [8,9]. In addition, the curvature of the plasma channel was taken into account.…”