Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches

Abstract

A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by a dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M ¼ 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al. [Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the ZT e of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well. V C 2013 American Institute of Physics. [http://dx

Shock-less interactions of ablation streams in tungsten wire array z-pinches

“…This method was successful in removing the majority of the artefacts and led to a significant improvement in the reliability of the resulting data. Although this method represents an improvement over the previous one, this change does not impact the validity of our previous work, 10 as it does not change the overall geometry of the shock structure. For comparison, Fig.…”

“…3(a) shows the results of this improved technique as applied to our previously published 32 wire aluminium array data. 10 …”

“…10,20 The positions of the fringe minima were traced for both the reference and experimental interferograms and this information was then used to construct interpolated maps of the relative fringe shift for each. The fringe shift produced by the plasma was then obtained by subtracting the reference fringe map from the experimental one.…”

“…In our previous paper, 10 we presented the results of experiments investigating the structures formed by the interactions of ablation streams in aluminium wire arrays, diagnosed using an imaging interferometry system aligned end-on to the array. The interferograms captured in these experiments showed that the electron density distributions were dominated by networks of oblique shock fronts, formed by the collisional interactions of neighbouring ablation streams as they converged towards the axis.…”

Experimental evidence for collisional shock formation via two obliquely merging supersonic plasma jets

“…Related studies include counter-streaming laser-produced plasmas supporting hohlraum design for indirect-drive inertial confinement fusion [17][18][19] and for studying astrophysically relevant shocks, [20][21][22][23][24] colliding plasmas using wire-array Z pinches, 25,26 and applications such as pulsed laser deposition 27 and laser-induced breakdown spectroscopy. 28 Primary issues of interest in these studies include the identification of shock formation, the formation of a stagnation layer [29][30][31] between colliding plasmas, and the possible role of two-fluid and kinetic effects on plasma interpenetration.…”