Electronic-topological transition and shear stability of the β alloys Ni-Al and TiNi

On the basis of a numerical calculation of the band contributions to the shear moduli, this paper discusses a hypothesis expressed earlier that the premartensitic softening of the lattice in Ni-Al and TiNi alloys is caused by the approach of the latter to an electronic-topological transition (ETT). It is found in both alloys that the ETT effects are substantially different in the different shear moduli: They are strong in the modulus C′ (especially in Ni-Al) and weak in C ₄₄. It can be concluded from this result that the observed premartensitic softening of C′ in Ni-Al and TiNi can actually be caused by the approach to the ETT point. At the same time, the anomalous temperature dependence of C ₄₄ observed in TiNi is apparently not associated with ETT effects. Fiz. Tverd. Tela (St. Petersburg) 39, 972–976 (June 1997)     

Spatial and temporal distribution of potential in the pseudosparkswitch

The understanding of emission and transport in the pseudospark is complex because these are related to a transition between two fundamentally different modes of electron emission. In this paper probe measurements of plasma parameters are presented providing evidence for oscillatory behavior of the current and potential during this transition. It is shown that these fluctuations are related to a glow-to-arc transition wherein smooth current growth is interrupted by cathode spot formation inside of the hollow cathode resulting in very rapid rise in current. These results support a view that quenching observed in the pseudospark is a double-layer phenomenon that occurs when emission cannot exceed secondary emission produced by ion bombardment     

Fast processes on cathode surface resulting in pseudosparkdischarge

An alternative mechanism for emission during the high-current phase of a pseudospark discharge is presented. A high current density is provided by multiple arc cathode spots which appear due to cathode-plasma breakdown. The model of plasma formation in the main gap of the pseudospark switch is discussed, together with conditions required for the initiation of spot during some tens of nanoseconds, the appearance of a moving double plasma layer, and high-current transport through the plasma-filled diode     

Observation of the luminescence between the electrodes during the rise in the spark current in a vacuum breakdown at constant voltage

The instants corresponding to the appearance of luminescence in three regions of the interelectrode gap (at the anode and cathode and in the center of the gap) were determined by means of a photomultiplier and compared with the onset of the rise in current during a dc spark vacuum breakdown. Only the luminescence at the cathode started at exactly the same moment as the rise in current. It appeared that the irreversible breakdown in the vacuum insulation during a dc breakdown was due to the development of cathode jets, as in the case of a pulsed discharge.Translated from Izvestiya VUZ, Fizika, No. 3, pp. 12–16, March, 1973.The authors wish to thank G. A. Mesyats for interest in this work and R. B. Baksht for active participation in discussing the results.     

High current density spotless vacuum arc as a glow discharge

Vacuum discharge burning between a broad cathode and a point anode made of Mo, Cu, and Cd has been studied. This discharge operates in anode vapors and shows major arc characteristics, although no craters were examined on the cathode. The secondary electron emission is involved to explain current transport within the cathode region. This discharge is interpreted as a high density low voltage glow discharge. Having discussed the present and previous findings, the conclusion has been drawn that the secondary electron emission and “hump of potential” are dominant in the vacuum arc cathode spot     

Near-cathode potential drop in a vacuum diode with explosive emission of electrons

The near-cathode potential drop u_K is studied in a high-voltage high-current (U=20–40 kV, i=100–500 A) vacuum diode with a cathode operating under explosive emission of electrons. The magnitude of U_K is estimated from oscillograms of the probe current under conditions of breakdown of the layer between the probe and the cathode-flare plasma. It is shown that u_K is the same order of magnitude as the near-cathode potential drop in vacuum arcs. U_K does not change greatly when there are sharp rises in diode current, indicating that oscillations in diode current are probably related to processes at the boundary for drawing of electrons from the flare plasma.