Characteristics of moderate current vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses

Abstract

A comparative study of the characteristics of moderate-current (∼10kA), low-energy (⩽20J) vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses is performed. Temporal profiles of the x-ray emission, discharge current, and anode voltage measured in vacuum discharge created between a planar titanium cathode and a conical point-tip anode are observed to be quite different for the two regimes of the laser pulse duration. While cathode plasma jet pinching is clearly observed in the discharge created by low-energy (∼5mJ), 27 ps full width at half-maximum (FWHM) laser pulses, a feeble pinching occurred for 4 ns (FWHM) laser pulses only above a threshold energy of ∼250mJ. In addition to the multiple K-shell x-ray pulses emitted from the titanium anode up to 100 ns, evidence of a much harder x-ray component (hν>100keV) is also seen in the discharge triggered by picosecond laser pulses.

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

“…2͒ indicates the formation of pinch ͑plasma point͒ at the cathode plasma jet front. [16][17][18] However, the observation of high-energy ions could not be solely attributed to the formation of pinch in the discharge as similar TOF ion signals were recorded for laserpulse energy in the range of 2-600 mJ, whereas formation of pinch at the front of cathode plasma jet was observed only for small laser pulse energies of ϳ2 -20 mJ. Moreover, the formation of pinch occurred much later, ϳ150-160 ns, after initiation of the 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.…”

“…This has also been confirmed by pin-hole imaging of the discharge gap. [16][17][18] Next, the TOF signals of ion were studied. Figure 3͑a͒ shows a typical TOF ion signal recorded for Al cathode for d = 13.5 mm at an anode voltage of 20 kV and laser pulse energy of 2-5 mJ.…”

“…[11][12][13][14][15] We have observed occurrence of cathode-plasma jet pinching in a moderate-current ͑few kiloamperes͒, lowenergy ͑Յ20 J͒ vacuum discharge triggered by 27 ps duration laser pulses. 16,17 Recently, we have reported the formation of single pinched plasma point in the cathode plasma jet of the discharge. 18 In this paper, we report a study on ion generation in the cathode plasma jet of the vacuum spark discharge using time of flight ͑TOF͒ technique and compare them with that observed from laser-produced plasma plume.…”

Laser triggering of spark gap switches with less than 100μJ’s of energy

“…Examples include 5mJ/20 kV [8], 1mJ/10kV [9], 6.2mJ/80kV [10], 1mJ/43kV [11], 3mJ/3.6kV [12], 10mJ/30kV [7], 3.4mJ/500kV [13] and 200nJ/84kV [14]. Low laser energy in itself is insufficient.…”