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Title: Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches

Abstract

The early stages of tungsten (W) wire-array Z-pinch implosions have been studied using two-frame point projection x-ray backlighting on the 1 MA COBRA pulsed power generator [J. D. Douglass, J. B. Greenly, D. A. Hammer, and B. R. Kusse, in Proceedings of the 15th IEEE International Pulsed Power Conference, Monterey, 2005 (to be published)]. X-pinch backlighter images with subnanosecond time resolution and 4-10 {mu}m spatial resolution have been obtained of individual W exploding wires in 8-wire arrays that show evolution of wire-core and coronal plasma structures. The timing of the X-pinch x-ray bursts relative to the Z-pinch initiation time was adjusted over a 50 ns time interval by varying the X-pinch mass per unit length. Wire-cores seen in two images separated in view by 120 deg. show that the expansion is remarkably azimuthally symmetric. A strong correlation is observed between the structure on the dense exploding wire-cores and the structure of the {>=}10{sup 18}/cm{sup 3} ablation plasma being drawn from radial prominences. Plasma ablation velocity was estimated to have a lower bound of 24 km/s. The wire-core expansion rate was found to be approximately constant with time over the interval 50-100 ns after the start of the current pulse. Finally,more » micron-scale axial gaps, seen as early as 70 ns into the current pulse and persisting from that time, were observed along the wire-core.« less

Authors:
; ;  [1]; ;  [1];  [2]; ;  [3]
  1. Laboratory of Plasma Studies, 439 Rhodes Hall, Cornell University, Ithaca, New York 14853 (United States)
  2. (Russian Federation)
  3. Blackett Laboratory, Imperial College, London SW7 2BZ (United Kingdom)
Publication Date:
OSTI Identifier:
20960109
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2431633; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABLATION; EXPANSION; EXPLODING WIRES; IMAGES; IMPLOSIONS; LENGTH; PLASMA; SPATIAL RESOLUTION; TIME RESOLUTION; TUNGSTEN; X RADIATION; X-RAY SOURCES

Citation Formats

Douglass, J. D., Hammer, D. A., McBride, R. D., Pikuz, S. A., Shelkovenko, T. A., P. N. Lebedev Physical Institute, Leninsky Prospect 53, Moscow 117924, Bland, S. N., and Bott, S. C. Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches. United States: N. p., 2007. Web. doi:10.1063/1.2431633.
Douglass, J. D., Hammer, D. A., McBride, R. D., Pikuz, S. A., Shelkovenko, T. A., P. N. Lebedev Physical Institute, Leninsky Prospect 53, Moscow 117924, Bland, S. N., & Bott, S. C. Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches. United States. doi:10.1063/1.2431633.
Douglass, J. D., Hammer, D. A., McBride, R. D., Pikuz, S. A., Shelkovenko, T. A., P. N. Lebedev Physical Institute, Leninsky Prospect 53, Moscow 117924, Bland, S. N., and Bott, S. C. Mon . "Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches". United States. doi:10.1063/1.2431633.
@article{osti_20960109,
title = {Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches},
author = {Douglass, J. D. and Hammer, D. A. and McBride, R. D. and Pikuz, S. A. and Shelkovenko, T. A. and P. N. Lebedev Physical Institute, Leninsky Prospect 53, Moscow 117924 and Bland, S. N. and Bott, S. C.},
abstractNote = {The early stages of tungsten (W) wire-array Z-pinch implosions have been studied using two-frame point projection x-ray backlighting on the 1 MA COBRA pulsed power generator [J. D. Douglass, J. B. Greenly, D. A. Hammer, and B. R. Kusse, in Proceedings of the 15th IEEE International Pulsed Power Conference, Monterey, 2005 (to be published)]. X-pinch backlighter images with subnanosecond time resolution and 4-10 {mu}m spatial resolution have been obtained of individual W exploding wires in 8-wire arrays that show evolution of wire-core and coronal plasma structures. The timing of the X-pinch x-ray bursts relative to the Z-pinch initiation time was adjusted over a 50 ns time interval by varying the X-pinch mass per unit length. Wire-cores seen in two images separated in view by 120 deg. show that the expansion is remarkably azimuthally symmetric. A strong correlation is observed between the structure on the dense exploding wire-cores and the structure of the {>=}10{sup 18}/cm{sup 3} ablation plasma being drawn from radial prominences. Plasma ablation velocity was estimated to have a lower bound of 24 km/s. The wire-core expansion rate was found to be approximately constant with time over the interval 50-100 ns after the start of the current pulse. Finally, micron-scale axial gaps, seen as early as 70 ns into the current pulse and persisting from that time, were observed along the wire-core.},
doi = {10.1063/1.2431633},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Shock-less dynamics were observed during the ablation phase in tungsten wire array experiments carried out on the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. This behaviour contrasts with the shock structures which were seen to dominate in previous experiments on aluminium arrays [Swadling et al., Phys. Plasmas 20, 022705 (2013)]. In this paper, we present experimental results and make comparisons both with calculations of the expected mean free paths for collisions between the ablation streams and with previously published Thomson scattering measurements of the plasma parameters in these arrays [Harvey-Thompson et al., Phys. Plasmas 19, 056303 (2012)].
  • A new wire array configuration has been used to create thin shell-like implosions in a cylindrical array. The setup introduces a {approx}5 kA, {approx}25 ns current prepulse followed by a {approx}140 ns current-free interval before the application of the main ({approx}1 MA) current pulse. The prepulse volumetrically heats the wires which expand to {approx}1 mm diameter leaving no dense wire core and without development of instabilities. The main current pulse then ionizes all the array mass resulting in suppression of the ablation phase, an accelerating implosion, and no trailing mass. Rayleigh-Taylor instability growth in the imploding plasma is inferred tomore » be seeded by {mu}m-scale perturbations on the surface of the wires. The absence of wire cores is found to be the critical factor in altering the implosion dynamics.« less
  • 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 amore » 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 = 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{sub 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.« less
  • Abstract not provided.