Influence of the laser plasma-expansion specific on a cathode jet formation and the current stability in a laser-ignited vacuum discharge

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.

Study of the possibility for increasing the emission of soft x-rays from the plasma of a low-energy vacuum discharge triggered by a laser

“…Figure 4 shows a spectrum obtained for discharge parameters U=16 kV, J=150 mJ, P=10 10 W cm −2 , and the spot diameter 700 μm (the 'soft' focusing mode). A comparison of figures 3 and 4 shows that in the soft focusing mode, the intensity of the spectrum increases 1.5-2 times as a whole, which is explained, according to [17], by an increase in the amount of the working substance evaporated by the laser beam with the greater diameter. In this case, the strongest (3-5 times) increase in the intensity of lines is observed in the region λ<60 Å, indicating the blue shift of the 'center of gravity' of the short-wavelength range of the spectrum.…”

“…Thus, these studies show that the increase in the discharge and laser pulse energy in the sharply focused laser beam cannot provide the increase in the plasma temperature. In connection with the assumed possibility of improving the parameters of the pinch plasma by increasing the area of the laser beam focal spot [17], series of experiments were performed in which all the three parameters, U, J and the focal beam diameter, were varied.…”

“…One of the possible ways to solve this problem is the defocusing of a laser beam ('soft' focusing mode), which leads to a transition from a spherical to a jet type of the cathodic plasma expansion into the interelectrode gap [17]. The latter can facilitate the compression of the plasma by the own magnetic field of the current due to a decrease in the radial velocity plasma expansion.…”

Micro-pinch formation and extreme ultraviolet emission of laser-induced discharge plasma*

“…Micro-pinch usually occurs near the front of cathode plasma jet in the first few hundreds of nanoseconds. [30] At this moment, a large part of plasma in the gap comes from the laser ablation, a small part comes from the current ablation, the plasma is mainly concentrated near the cathode, the current is relatively low, only a small part of the plasma can satisfy the relationship: P m > P t , therefore only a 'neck' or a 'point' zone of high temperature forms.…”

Determining the spatial distribution of laser-induced plasma by laser-induced voltaic measurement

“…The * Authors to whom any correspondence should be addressed. generation process of LIP is instantaneous, which involves complex physical processes during the laser-matter interaction, plasma formation and subsequent expansion [10][11][12][13]. Understanding these processes in LIPs is beneficial for the further optimization and development of different applications.…”