Axial plasma jet characterization on a microsecond x-pinch

Abstract

The jets produced on a microsecond x-pinch (quarter period T1/4 ∼ 1 μs, dI/dt ∼ 0.35 kA/ns) have been studied through light-field schlieren imaging and optical framing photographs across 4 different materials: Al, Ti, Mo, and W. The axial velocity of the jets was measured and exhibited no dependence on atomic number (Z) of the wire material. There may be a dependence on another factor(s), namely, the current rise rate. The average axial jet velocity across all four materials was measured to be 2.9 ± 0.5 × 106 cm/s. The average jet diameter and the average radial jet expansion rate displayed inverse relationships with Z, which may be attributed to radiative cooling and inertia. Asymmetry between the anode and cathode jet behavior was observed and is thought to be caused by electron beam activity. The mean divergence angle of the jet was found to vary with wire material and correlated inversely with the thermal conductivity of the cold wire. Optical images indicated a two-layer structure in Al jets which may be caused by standing shocks and resemble phenomena observed in astrophysical jet formation and collimation. Kinks in the jets have also been observed which may be caused by m = 1 MHD instability modes or by the interaction of the jet with the electrode plasma.

A numerical study on laboratory plasma dynamics validated by low current x-pinch experiments

“…This discrepancy is justified by the fact that the radiative explosion effect which takes place this time period of the plasma dynamics is not considered in the simulation. However, the compression velocity (~11.5 km s −1 ) is very well predicted in agreement with the experimental data of this study and also of other studies [5].…”

“…The simulation results show exactly the same expansion velocity. This is an effective velocity, due to the contribution of the coronal plasma ablation in the jet bulk density, that compared to the simulated sound speed at the jet tip results to a Mach number equal to 4, that is consistent to relative works [5,61].…”

“…Pulsed power plasma devices loaded as Zpinch, x-pinch, wire arrays or liners, have the ability to reproduce a vast variety of plasmas, among others dense plasmas for fusion studies, laboratory astrophysics plasmas, dense and hot point source plasmas for hard x-ray generation and lower density hot plasmas. Such plasma production is essential for basic plasma physics studies like for instance plasma instabilities generation but also for important plasma applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”

High performance simulations of a single X-pinch

“…Figure 2 shows typical simulation results of the plasma density distributions on the slices through the plane of the wires at three consecutive times (20 ns, 40 ns and 60 ns), to provide insights on the plasma evolution from the current start, until the late times of the pinching effect and the plasma electrode gap formation [4,32,49,[68][69][70][71][72]. The velocity in vector representation is shown on the density contours.…”

“…At 40 ns, under the action of the Lorentz force on the smaller mass areas of the neck, two tightly compressed regions at ±0.08 mm from the cross point are observed. Moreover, an isolated island of plasma is also generated at the centre of this region by both codes [4,32,68,71,72]. The expansion of the density island is computed by GORGON to have a width of 0.70 mm and a height of 0.16 mm while the PLUTO simulation results demonstrate a width of 0.44 mm, and a height of 0.10 mm.…”