A relation between the mean average energy of accelerated ions epsilon i and the maximum rate of current rise in a vacuum discharge is established. The relationship takes the power form epsilon i varies as i1.3 for different ion species over a wide range of discharge parameters for i>i0=3*108 A s-1. For smaller values of i the corresponding value of epsilon i is almost independent of the discharge parameters. The ion mass and charge-dependence of epsilon i are also discussed.

The report presents the results from experimental investigation of micropinch formation in the plasma of a vacuum discharge induced by a 6 ns laser pulse of energy J = 0.5–200 mJ (at a storage voltage from 4 to 15 kV and the discharge current range of 6–26 kA, respectively). The discharge gap images were obtained using a pinhole camera in the EUV and soft X-ray ranges of 15–73 eV and 80–284 eV energy. It is shown that micropinch formation in the plasma cathode jet occurs, mainly, in the matter evaporated by the laser pulse at the discharge ignition near the moment when the current derivative reaches the maximum. It is found that the cathode jet may consist of several pinched areas, and each of them has its own structure, and the improvement of the discharge and laser radiation parameters allows us to reach a stable single pinching of plasma. The parameters of the micropinch (the plasma compression ratio, size, and position of the emitting area in the interelectrode gap) as well as the current flow through the interelectrode gap, at the given storage voltage, are completely governed by the laser radiation characteristics.

An analysis of a wide set of events, which have been observed in cathode plasma jet of vacuum arcs and sparks, is presented. In particular, they are (i) the substantial decrease of cross-section of cathode jet in a steady-state vacuum arc far from the cathode, (ii) the appearance of high charge states of ions under discharge current increase and pulse duration decrease and (iii) the significant enhancement of the energy of ions in cathode plasma jet with increase of the current rise rate and of the interelectrode gap length. We concluded that these effects, revealed within a wide range of discharge parameters, are similar in nature and could be explained by cathode plasma jet pinching out of the near-cathode region. This qualitative conclusion was supported by quantitative estimation of magnetic compression influence on plasma properties. Such estimations were obtained from theoretical models which have been developed to describe both the steady-state jet and a jet with increasing current.

No abstract

The travel of plasma flow produced by a dc arc through a transport system based on a curved magnetic field was studied. The characteristics of the system were the absence of a curved metallic plasma guiding duct ('open architecture') and the fact that the magnetic field coils were non-coaxial to the plasma flow. By means of Langmuir probe measurements it was shown that both shape and position of the cathode plasma flow at the exit of the transport system were governed by variation of currents of the magnetic coils as well as by biasing of a special electrode inserted into the plasma flow. It was found that with parameters of the transport system held constant, the plasma ions with lower m/Z were deflected more, e.g. Al ions were deflected more than Ti ions. For an arc with a composite cathode, consisting of mainly Cr-Fe-Ni, the profile of atoms of these elements at the exit of the transport system was measured by x-ray fluorescence spectrometry. The results obtained were consistent with the probe measurements, hence the transport system, in principle, may be used for spatial separation of a multi-component (in masses) plasma flow.

Ion parameters in a cathode plasma jet of a vacuum spark with a discharge energy of a few joules were measured. The studies were performed by a time-of-flight method with the help of an energy analyser. It was found that the discharge plasma generated a short-run beam of multiply charged ions of the cathode material at the initial stage of the discharge firing. The ions had charge states from Z = + 1 up to Z = + 18. When the initial capacitor voltage was varied within the ranges of 0.3-2.5 kV, the mean ion charge increased from +4.3 to +9.0.

No abstract

The formation of a current-plasma shell is studied during the expansion of a laser-ignited low-power vacuum-discharge cathode plasma jet into the interelectrode gap. The shell geometry is found to be determined by the mode of laser-plasma expansion at the discharge ignition stage. It is shown that the increase in the laser-beam focal spot area on the cathode surface leads to the increase in the matter density and the decrease in the density gradient in the discharge gap and to transition from the spherical laser-plasma expansion mode to the jet mode. The latter considerably stabilizes the current transfer in the discharge plasma, even during the development of the hydrodynamic sausage instability in it.