Design and modeling of precision solid liner experiments on Pegasus

Bowers, R.L.; Brownell, J. H.; Lee, H.; McLenithan, K. D.; Scannapieco, A. J.; Shanahan, William R.

doi:10.1063/1.367230

Cited by 23 publications

(3 citation statements)

References 4 publications

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“…End-effect instabilities were first identified as potentially problematic for MagLIF liners in Ref. [8], though others had previously observed them [82,83] and developed mitigation strategies such as conical electrode surfaces (referred to as "glide planes") [84][85][86].…”

Section: Liner Implosion Design Work To Improve Implosion Stability Amentioning

confidence: 99%

Implementing and diagnosing magnetic flux compression on the Z pulsed power accelerator

McBride

Bliss

Gómez

et al. 2015

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We report on the progress made to date for a Laboratory Directed Research and Development (LDRD) project aimed at diagnosing magnetic flux compression on the Z pulsed-power accelerator (0-20 MA in 100 ns). Each experiment consisted of an initially solid Be or Al liner (cylindrical tube), which was imploded using the Z accelerator's drive current (0-20 MA in 100 ns). The imploding liner compresses a 10-T axial seed field, B z (0), supplied by an independently driven Helmholtz coil pair. Assuming perfect flux conservation, the axial field amplification should be well described by B z (t) = B z (0) × [R(0)/R(t)] 2 , where R is the liner's inner surface radius. With perfect flux conservation, B z (t) and dB z /dt values exceeding 10 4 T and 10 12 T/s, respectively, are expected. These large values, the diminishing liner volume, and the harsh environment on Z, make it particularly challenging to measure these fields. We report on our latest efforts to do so using three primary techniques: (1) micro B-dot probes to measure the fringe fields associated with flux compression, (2) streaked visible Zeeman absorption spectroscopy, and (3) fiber-based Faraday rotation. We also mention two new techniques that make use of the neutron diagnostics suite on Z. These techniques were not developed under this LDRD, but they could influence how we prioritize our efforts to diagnose magnetic flux compression on Z in the future. The first technique is based on the yield ratio of secondary DT to primary DD reactions. The second technique makes use of the secondary DT neutron time-of-flight energy spectra. Both of these techniques have been used successfully to infer the degree of magnetization at stagnation in fully integrated Magnetized Liner Inertial Fusion (MagLIF) experiments on Z [

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Section: Liner Implosion Design Work To Improve Implosion Stability Amentioning

confidence: 99%

Implementing and diagnosing magnetic flux compression on the Z pulsed power accelerator

McBride

Bliss

Gómez

et al. 2015

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“…Numerical simulations of each experiment were performed using a 2-D Eulerian MHD code [15]. The calculation used the initial liner geometry including perturbations, the experimentally measured current history, tabular equation-of-state data, and a material strength formulation following Steinberg [12], [16].…”

Section: Two-dimensional Numerical Simulationsmentioning

confidence: 99%

Instability growth in magnetically imploded high-conductivity cylindrical liners with material strength

Reinovsky

Anderson

Atchison

et al. 2002

IEEE Trans. Plasma Sci.

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Magnetically imploded cylindrical metal shells ( -pinch liners) are attractive drivers for experiments exploring hydrodynamics and properties of materials at extreme conditions. As in all -pinches, the outer surface of a liner is unstable to magneto Rayleigh-Taylor (RT) modes during acceleration, and large-scale distortion arising from RT modes could make such liners unuseable. On the other hand, material strength in the liner should, from first principles, reduce the growth rate of RT modes, and material strength can render some combinations of wavelength and amplitude analytically stable. A series of experiments has been conducted in which high-conductivity, soft, cylindrical aluminum liners were accelerated with 6-MA, 7-s rise-time driving currents. Small perturbations were machined into the outer surface of the liner and perturbation growth monitored. Two-dimensional magneto-hydrodynamic (2-D-MHD) calculations of the growth of the initial perturbations were in good agreement with experimentally observed perturbation growth through the entire course of the implosions. In general, for high-conductivity and soft materials, theory and simulation adequately predicted the behavior of magneto-RT modes in liners where elastic-plastic behavior applies. This is the first direct verification of the growth of magneto-RT in solids with strength known to the authors.

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“…Experimental characterization of a converging shockwave in a cylindrical geometry provides fundamental benchmarks used in the modeling of 1-D and 2-D hydrodynamic phenomena from high or solid density implosions [1,2]. A high-speed laser shadowgraphy system for detailed imaging of a convergent cylindrical shockwave provides diagnosis where multiple sampling of the shock front position and radial shape are desired.…”

Section: Introductionmentioning

confidence: 99%

Development and fielding of high-speed laser shadowgraphy for electro-magnetically driven cylindrical implosions

Rodriguez

Roberts

Taylor

et al.

PPPS-2001 Pulsed Power Plasma Science 2001. 28th IEEE International Conference on Plasma Science and 13th IEEE International Pu

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A laser shadowgraphy system for high-speed imaging of a convergent cylindrical shockwave generated by an electro-magnetically driven solid density liner implosion in Lucite is described. The laser shadowgraphy system utilizes an advanced high-energy, long-pulse, frequencydoubled Nd:YAG laser for target illumination and a fast framing camera for multiple frame imaging of the shockwave as it radially converges and transits the Lucite. The time window resolution is 10 ns as determined by the fastest exposure time capable with the camera. Two onaxis symmetric implosions and two off-axis antisymmetric implosion experiments were fielded at the Air Force Research Laboratory's Shiva Star 4.2 MJ capacitor bank z-pinch facility. For each experimental shot, the shadowgraphy system captured several frames of shadowgraph images as the shockwave moved through the Lucite. Analysis of the shockwave shadowgraph image shapes is done by fitting each shadowgraph image to a generic elliptical fit function and plotting the resultant 2-D image fits for comparison. For the on-axis symmetric implosion shots, a radial shock velocity is calculated. The Lucite shock speed is seen to increase monotonically from an initial velocity of 7.9 mm/µs to a near final velocity of 13.4 mm/µs as convergence effects dominate the shock speed calculated at small radii.

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Design and modeling of precision solid liner experiments on Pegasus

Cited by 23 publications

References 4 publications

Implementing and diagnosing magnetic flux compression on the Z pulsed power accelerator

Implementing and diagnosing magnetic flux compression on the Z pulsed power accelerator

Instability growth in magnetically imploded high-conductivity cylindrical liners with material strength

Development and fielding of high-speed laser shadowgraphy for electro-magnetically driven cylindrical implosions

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