A Review of Anode Phenomena in Vacuum Arcs

Abstract

This paper discusses arc modes at the anode, experimental results pertinent t o anode phenomena, and theoretical explanations of anode phenomena.A vacuum arc can exhibit five anode discharge modes: (1) a low current mode in which the anode is basically passive, acting only as a collector of particles emitted from the cathode; (2) a second low current mode that can occur if the electrode material is readily sputtered (a flux of sputtered atoms will be emitted by the anode); (3) a footpoint mode, characterized by the appearance of one or more small luminous spota on the anode (footpoints are generally much cooler than the true anode spota present in the last two modes); (4) an anode spot mode in which one large or several small anode spots are present (such spots are very luminous, have a temperature near the atmospheric boiling point of the anode material, and are a copious source of vapor and ions); and ( 5 ) an intense arc mode where an anode spot is present, but accompanied by severe cathode erosion.The arc voltage is relatively low and quiet in the two low current. modes and the intense arc mode. It is usunlly high and noisy in the footpoint mode, and it can be either in the anode spot mode. Anode erosion is low, indeed negative, in the two low current modes, and it is low to moderate in thc footpoint mode. Severe anode erosion occurs in both the anode spot and intense arc modes.The dominant mechanism controlling the formation of an anode spot appears to depend upon the electrode geometry, the electrode material, and the current waveform of the particular vacuum i i rc being considered. I n specific experimental conditions, either magnetic constriction in the gap plasma, or gross anode melting, or local snode evaporation can trigger the transition. However, the most probable explanation of anode spot formation is a combination theory, which considers magnetic constriction in the plasma together with the fluxes of material from the anode and cathode as well as the thermal, electricnl, and geometric effects of the anode in analyzing the behavior of the anode and the nearby plasmn.

A hot refractory anode vacuum arc: nonstationary plasma model

“…1). was obtained by balancing re-evaporation from the anode with the radial plasma from the interelectrode gap: (2) where gap width; atom mass; radial plasma velocity at the radial boundary of the gap. In (2), the radial plasma flux is assumed to be singly charged ions, i.e., it was assumed that the plasma is highly, but singly, ionized [10].…”

“…The HAVA has been reviewed by Miller [2] and studied in detail by Erich et al [3]- [7]. In the HAVA, the metallic vapor is produced by anodic evaporation [3], [7].…”

High-current vacuum arc: The relationship between anode phenomena and the average opening velocity of vacuum interrupter

“…Anode plays an active role in the transition process of the discharge. Miller [1][2][3][4] pointed out that the vacuum arcs exhibit two low-current anode discharge modes and three high-current anode discharge modes. The transition from a low-current anode mode to a high-current anode mode depends on the contact material, the contact geometry (contact diameter, contact gap, etc.…”

“…The parameters influencing formation of an anode footpoint and/or an anode spot are well established [3] . I c , the current at which an anode spot forms, increases with the anode diameter and decreases with the contact gap [3] .…”

“…In the two low-current anode modes the anode is basically passive or the anode emits a flux of sputtered atoms. The three high-current anode discharge modes include a footpoint mode, an anode spot mode and an intense arc mode [1][2][3][4] .…”