Effect of the global to local magnetic field ratio on the ablation modulations on X-pinches driven by 80 kA peak current

Abstract

We report the results of experiments where a quantitative analysis of the behavior of ablation modulations in X-pinches (including wavelength and contrast between streams) was carried out as a function of distance from the cross-point, and consequently, as a function of the global to local magnetic field ratio. Experiments were performed using two tungsten wires of 10 µm diameter in an X-pinch configuration on a pulsed power generator capable of producing an 80 kA current over a 50 ns rise time. We compare these findings directly to three-dimensional magneto-hydrodynamic (MHD) simulations using the MHD resistive code GORGON. Here, we demonstrate a dependence between the magnetic field ratio and ablation properties, suggesting a transition to a classical m = 0 instability far from the cross-point. Additionally, we examine the ablation properties of similar Z number nickel and copper wire X-pinches.

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

“…The momentum and the J × B force have a common origin located at the tail of the arrows. The influence of the J × B force is discussed, taking into account the local and global magnetic field dynamics [19,20,65]. The J × B force units are in Gauss 2 and the scaling factor used is c∆l/4π, where c is the speed of light (in CGS) and ∆l = 0.001 cm is the unit length used in the simulation.…”

“…Various numerical codes have been developed and evolved in order to describe the physical behavior of plasmas. Purely Eulerian grid codes like GORGON [15][16][17][18][19][20][21][22], purely Lagrangian like MULTI-2D [23][24][25] or arbitrary Lagrangian Eulerian (ALE) codes like ALEGRA [26][27][28][29] and MACH2 [30,31], are capable to describe astrophysical and laboratory plasmas. Also, codes like ATHENA and ZEUS or FLASH, were evaluated and tested among others in the Noh Z-Pinch problem and implosion dynamics of wire-array Z-pinches [32][33][34].…”

“…Most of the developed approximation models combine the hydrodynamics and Maxwell's equations in moving media with displacement currents neglected [24][25][26][27][28][29][35][36][37], hence the values of the magnetic field at the boundaries are subjected to instant modification since retaining fields do not exist. When displacement currents are included, the complete electromagnetic equations are considered, thus the boundary conditions are imposed in accordance to the propagation of the electromagnetic waves [7,[15][16][17][18][19][20][21][22].…”

Investigation into the dynamics of laser-cut foil X-pinches and their potential use for high repetition rate operation

“…This likely explains the strong periodic streams propagating to the axis all along the legs later in time, as opposed to previous observations of m ¼ 0 instabilities along the wires far from the cross-point. 19 As no work has been done to examine the dynamics of tantalum wire Xpinches or arrays, there is no data for comparison to the results presented here. Figure 3(a) shows a radiograph from a Ta foil X-pinch with three meshes of different void and wire widths.…”

“…Tapering added strength and reduced the likelihood of pinching along the X-pinch limbs as was observed in previous experiments. 19 The finished foil X-pinch had extra tabs on the left and right of the cross-point to support the array during loading into the electrodes. The tabs were removed after securing the electrode-target assembly in the vacuum chamber.…”