Snowplow-like behavior in the implosion phase of wire array Z pinches

Lebedev, S. V.; Beg, F. N.; Bland, S. N.; Chittenden, J. P.; Dangor, A. E.; Haines, M. G.

doi:10.1063/1.1466466

Cited by 108 publications

(73 citation statements)

References 24 publications

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“…The breaks form at this time due to the highly non-uniform ablation rate along the length of the wires; the ablation rate is modulated at a predictable "fundamental" wavelength. 6,7 Once the wires are broken the array undergoes a snowplough like implosion, 8,9 followed by the stagnation of the accrued kinetic energy as an intense pulse of soft x-ray radiation. 10,11 This paper presents the results of a series of experiments conducted in order to investigate the dynamics of wire array plasmas during the ablation phase.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2013

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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

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Section: Introductionmentioning

confidence: 99%

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

et al. 2013

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“…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. In addition, an increase of the wire number, up to the optimum, improves symmetry which in turn makes the implosion and stagnation even more stable.…”

Section: B Stagnated Plasma Scalingmentioning

confidence: 77%

“…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. …”

Section: Discussion Of the Results And Comparison With 2d And 3d mentioning

confidence: 99%

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

et al. 2011

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We report results of the experimental campaign, which studied the initiation, implosion dynamics, and radiation yield of tungsten wire arrays as a function of the wire number. The wire array dimensions and mass were those of interest for the Z-pinch driven Inertial Confinement Fusion (ICF) program. An optimization study of the x-ray emitted peak power, rise time, and full width at half maximum was effectuated by varying the wire number while keeping the total array mass constant and equal to $5.8 mg. The driver utilized was the $20-MA Z accelerator before refurbishment in its usual short pulse mode of 100 ns. We studied single arrays of 20-mm diameter and 1-cm height. The smaller wire number studied was 30 and the largest 600. It appears that 600 is the highest achievable wire number with present day's technology. Radial and axial diagnostics were utilized including crystal monochromatic x-ray backlighter. An optimum wire number of $375 was observed which was very close to the routinely utilized 300 for the ICF program in Sandia.

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“…Importantly, ablation proceeds in a nonuniform way along each wire, with an axial modulation of the ablation rate. This creates highly non-uniform initial conditions for the main (snowplough-like) implosion phase, 22 causing some fraction of the array mass to be left behind at large radius. This trailing mass limits the convergence of the current toward the axis, and hence limits x-ray power produced at stagnation of the pinch.…”

Section: Introductionmentioning

confidence: 99%

Characterisation of the current switch mechanism in two-stage wire array Z-pinches

et al. 2015

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In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA, 240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inverse wire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wire array, before rapidly switching the majority of the generator current into the load after a 100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse is presented. Measurements of the load resistivity and energy deposition suggest significant bulk heating of the array mass occurs. The ∼5 kA pre-pulse delivers ∼0.8 J of energy to the load, leaving it in a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse array begins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicate that the main current switch may evolve in part as a plasma flow switch, driven by the expansion of a magnetic cavity and plasma bubble along the length of the load array. Analysis of implosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, corresponding to a doubling of the generator dI/dt. Potential scaling of the device to higher current machines is discussed.

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Snowplow-like behavior in the implosion phase of wire array Z pinches

Cited by 108 publications

References 24 publications

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

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

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

Characterisation of the current switch mechanism in two-stage wire array Z-pinches

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