Pinch effect in vacuum arc plasma sources under moderate discharge currents

Abstract

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.

Fast ion generation in the cathode plasma jet of a multipicosecond laser-triggered vacuum discharge

“…1,2,[16][17][18] The process of occurrence of cathode plasma jet pinching in a vacuum discharge may be broadly understood as follows. 2 The process begins with the trigger pulse ͑electrical/laser͒ creating the cathode plasma, which starts expanding toward the anode. Initially the temperature and density of the plasma are high so that thermal plasma pressure is much higher than the pressure exerted by the self-generated magnetic field.…”

“…19,20 However, there is no common understanding about the origin of the high-energy ions. 2,14,15,21 Along with high-energy protons of ϳ4 -5 MeV, carbon ͑Z max =4͒ and aluminum ͑Z max =6͒ ions of 10-15 MeV energy were observed by Plyutto, for applied anode voltage of ϳ300 kV, for a diode gap of 1-2 cm. In the recent experiments 11 performed at Irkutsk State University ͑ISU͒, Russia, generation of multiple charged ions of the cathode material has been reported in a small-voltage ͑up to 2.5 kV͒, low-energy ͑up to 10 J͒ electrical-triggered vacuum spark discharge.…”

“…9,10 A different mode of pinch effect, viz., cathode plasma jet pinching, has been observed in moderate-current ͑few hundreds of amperes to few kiloamperes͒ vacuum arcs and sparks. 2 In this case, pinching occurs in the cathode plasma jet expanding with a free boundary, whereas in the highcurrent ͑ϳ100 kA͒ discharges discussed previously, it occurs in the plasma column bound by the electrodes after shorting of the diode gap. Generation of high-energy, multiple-charged ions of cathode material has also been reported in vacuum sparks and arcs associated with occurrence of cathode plasma jet pinching.…”

Ion acceleration in vacuum arc cathode plasma jets with large rates of current rise

“…An important question is the mechanism of plasma acceleration in the cathode jets. Recently, in short pulsed high-current vacuum arcs [2], [3] and earlier for sparks [4], [5], a considerable increase of the ion energy in comparison to longer duration low current arcs has been observed. The measured ion energy range in microsecond arcs with current is 1-10 keV (high energy) while for I, 100-A millisecond arcs it is only about 100 eV (low energy) [6]- [8].…”

Source of metal ions with a variable velocity

“…Fig.Z(a)presents a typical plot of the discharge current for the initial capacitor voltage of 0.8 kV andFig.2(b)shows the corresponding signal h m the %-a Lyd4 The scheme of experiments. 1, capacitor; 2, cathode; 3, anode; 4, igniter; 5, suppressing grid ; 7,collector, collector.…”