Pulsed dye laser diagnostics of vacuum arc cathode spots

The ignition and arc phases of vacuum arcs were investigated using differential dye laser absorption photography with simultaneous high spatial (micrometer) and temporal (nanosecond) resolution. The discharge duration was 800 ns, the current 50-150 A, the electrode material copper, and the cathode-anode distance less than 50 mu m. A 0.4 ns laser pulse (tunable, gamma =480-530 nm) was used to obtain momentary absorption photographs of the cathode region. During ignition, an optically thick anode plasma expanded toward the cathode, decaying within 25 ns after bridging the electrode gap. In the arc phase, a fragmentary structure of the cathode spots was observed in situ for the first time. The microspots have a characteristic size of 5-10 mu m. They appear and disappear on a nanosecond time scale. The plasma density of the microspots was estimated to be greater than (3-6)*10/sup 26/ m/sup -3/. >

[1]  A. Anders.  A Formulary for Plasma Physics , 1990 .

[2]  P. Siemroth,et al.  Investigations of the Current Density in the Cathode Spot of a Vacuum Arc , 1985 .

[3]  B. Djakov,et al.  Cathode spot structure and dynamics in low-current vacuum arcs , 1974 .

[4]  N. B. Volkov,et al.  The ionic composition of the non-ideal plasma produced by a metallic sphere isothermally expanding into vacuum , 1991 .

[5]  V. Rakhovsky.  Critical parameters of the cathode region of a vacuum arc , 1990 .

[6]  B. Juttner,et al.  Current Density in Arc Spots , 1985, IEEE Transactions on Plasma Science.

[7]  C. Wieckert.  The expansion of the cathode spot plasma in vacuum arc discharges , 1987 .

[8]  V. Puchkarev,et al.  Current density and the cathode spot lifetime in a vacuum arc at threshold currents , 1990 .

[9]  A. Anders,et al.  Vacuum arc cathode spot parameters from high‐resolution luminosity measurements , 1992 .

[10]  L. Sena.  Fission of the Cathode Spot of a Low-Pressure Arc , 1971 .

[11]  J. Daalder.  Diameter and Current Density of Single and Multiple Cathode Discharges in Vacuum , 1974 .

[12]  B. Juttner.  Formation time and heating mechanism of arc cathode craters in vacuum , 1981 .

[13]  G. A. Lyubimov,et al.  The cathode spot of a vacuum arc , 1978 .

[14]  B. Juttner.  Characterization of the Cathode Spot , 1987, IEEE Transactions on Plasma Science.

[15]  S. Anders.  On the State of Ionization, Non-Ideality and Electric Conductivity of the Cathode Plasma of Vacuum Arcs , 1986 .

[16]  G. Mesyats,et al.  REVIEWS OF TOPICAL PROBLEMS: Field emission and explosive electron emission processes in vacuum discharges , 1983 .

[17]  C. Wieckert.  A Multicomponent Theory of the Cathodic Plasma Jet in Vacuum Arcs , 1987 .

[18]  S. Anders,et al.  Arc cathode processes in the transition region between vacuum arcs and gaseous arcs , 1987 .

[19]  A. Anders,et al.  Emission spectroscopy of low-current vacuum arcs , 1991 .

[20]  H. Hess.  The vacuum arc spot-a high pressure phenomenon , 1991 .

[21]  B. Juttner,et al.  Erosion Craters and Arc Cathode Spots in Vacuum , 1979 .

[22]  K. Riemann.  Theory of the cathode sheath in a vacuum arc , 1989 .