The vacuum arc spot-a high pressure phenomenon

Abstract

Inertial confinement is assumed for the initial phase of the cathode spot of a vacuum arc in the case of fast heating. The plasma is therefore isochorically heated (up to 20000 K), leading to pressures of about 10 GPa. The spot plasma is strongly coupled, so the effective ionization energies of the first successive steps of ionization tend to zero. This may explain the highly charged ions found in vacuum discharges despite the low plasma spot temperature derived here. The spot plasma parameters obtained from the condition of fast heating agree quite well with values obtained in other ways for the explosive mode of development of the vacuum arc plasma.

Detailed numerical simulation of cathode spots in vacuum arcs: Interplay of different mechanisms and ejection of droplets

“…models of vacuum arc-cathode interactions that assume a continuous metal-plasma transition without an interface. [47][48][49] The approach to the modeling of cathode spots employed in this work does not assume a continuous metal-plasma transition nor do the modeling results reveal microexplosions, but the question as to whether a wide-range EOS should be implemented is still relevant.…”

Comment on `Ignition of a welding arc during a short-circuit of melted electrodes'

“…However, they neither furnished any direct evidence in support of their hypothesis nor did they mention pertaining details published by other authors who dealt with the issues concerned (e.g. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]).…”

“…Other authors, except [9], share the opposite point of view that ignition of the arc is always mediated by an explosion out of the liquid metal bridge. Explosion and ignition inevitably coincide, both locally and temporally, not just in welding but also with exploding wires [7]. Furthermore, it has been commonly accepted that the explosion is closely linked with the occurrence of highly unwelcome spatter.…”

“…With 100 A and 0.01 mm diameter, the axial pressure due to the own magnetic field can easily be calculated to exceed the atmospheric pressure by a factor of 12.6! A paper by Hess [7] can be recommended for those who are not aware of the crucial role played by isochoric heating in the case of confinement largely by inertia. Such dynamic confinement can quickly lead to a pressure and a temperature as high as 10 GPa (far over the critical point for the liquid-gas transition) and 20 000 K, respectively.…”

“…It would also not be worth quarrelling about how, in detail, the detonation creates ions. For information concerning the threshold temperature for the transition from liquid into the plasma state, I refer the reader to the paper by Hess [7].…”