Experiments measuring the initial energy deposition, expansion rates and morphology of exploding wires with about 1 kA/wire

Abstract

Wire-array Z-pinch implosion experiments begin with wire heating, explosion, and plasma formation phases that are driven by an initial 50–100 ns, 0–1 kA/wire portion of the current pulse. This paper presents expansion rates for the dense, exploding wire cores for several wire materials under these conditions, with and without insulating coatings, and shows that these rates are related to the energy deposition prior to plasma formation around the wire. The most rapid and uniform expansion occurs for wires in which the initial energy deposition is a substantial fraction of the energy required to completely vaporize the wire. Conversely, wire materials with less energy deposition relative to the vaporization energy show complex internal structure and the slowest, most nonuniform expansion. This paper also presents calibrated radial density profiles for some Ag wire explosions, and structural details present in some wire explosions, such as foam-like appearance, stratified layers and gaps.

Wire number dependence of the implosion dynamics, stagnation, and radiation output of tungsten wire arrays at Z driver

“…31 When the wire number becomes larger than the optimum number ($375 6 25), the wire cores start merging very early during the prepulse stage of the load current pulse, the precursor plasma inside the array becomes negligible or non-existent, and the wire array pinches as a thin shell which is prone to instabilities. Applying this explanation to W and Al experimental results, we estimate wire core sizes and core expansion velocities close to those independently measured in Imperial College and Cornell University, 28,29,33,34 This finding further reinforces the plausibility of our speculations. In addition, analytical calculations 35 and 2D model simulations 26 suggest the enhanced Z-pinch stability due to plasma distribution inside the array prior the onset of wire motion.…”

“…These estimates are in reasonably good agreement with the independently measured core sizes for both materials. 28,[31][32][33][34] The above discussion suggests that the optimum IWG op is the gap where the wire coronas merge very early during the prepulse stage of the load current pulse, the precursor plasma inside the array becomes negligible or non-existent, and the wire array pinches as a thin ($50l for W and $220l for Al) shell. Analytical calculations 35 and 2D model simulations 26 support this assumption and suggest that the plasma distribution inside the array, prior to the onset of the wire motion, enhances the pinch stability.…”

Ablation dynamics in wire array Z-pinches under modifications on global magnetic field topology

“…Since $1 kA/wire is needed for breakdown, the influence of different resistances should impact on the energy deposited on the solid wires mainly during the first $10 ns of the discharge, until the very low resistivity coronal plasma conducts the greater part of the current. 22,23 In any case, the resolution of the electrical diagnostics is limited by the use of an integrator circuit for the Rogowski coil and the level of electrical noise at very early times. On the contrary, during most of discharge, it can be assumed that the load current is divided on the wires based on their self-inductance ratio considering them as parallel inductors for the load.…”

Experimental observation of plasma formation and current transfer in fine wire expansion experiments.

“…Before the magnetic pressure is large enough to cause implosion the individual wires melt, vaporize and expand 3,4 .…”