Investigation of ablation and implosion dynamics in linear wire arrays

Иванов, В. В.; Sotnikov, V. I.; Haboub, A.; Sarkisov, G.; Presura, R.; Cowan, T. E.

doi:10.1063/1.2716665

Cited by 20 publications

(24 citation statements)

References 23 publications

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“…Inductive current division still allows current to be distributed throughout the wires in a planar array, but causes current to peak in the few wires near the edge of the array with the outermost wires carrying a factor of 2-3 times more current than the innermost wires [27]. We expect this to be the most reasonable assumption for planar arrays, given the observations that the inner wires ablate and so must carry some current [6], but also that the inner wires experience little acceleration while the implosion commences at the outer wires and cascades inward [7] implying that somewhat less current flows in the inner wires. Modeling with inductive division best reproduces the latter observation.…”

Section: Return Current Cagementioning

confidence: 99%

“…The planar array distributes the initial mass profile radially, which is not intuitively optimal for providing high implosion velocity. Laser shadowgraphy indicates, however, that the wires implode in a cascade, with magnetic Rayleigh-Taylor implosion instabilities being stabilized to some extent as the implosion front impacts each adjacent wire on its way toward the axis [7]. This may suggest that a linear array mitigates instabilities as a multiply nested wire array; nested cylindrical wire arrays have been previously demonstrated to enhance the radiated x-ray power and shorten the pulse due to mitigation of the magnetic Rayleigh-Taylor implosion instability [1] as the current is switched from the outer to the inner array during the implosion [8].…”

Section: Introductionmentioning

confidence: 99%

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Planar wire array performance scaling at multi-MA levels on the Saturn generator.

Chuvatin

Jones²,

Vesey³

et al. 2007

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A series of twelve shots were performed on the Saturn generator in order to conduct an initial evaluation of the planar wire array z-pinch concept at multi-MA current levels. Planar wire arrays, in which all wires lie in a single plane, could offer advantages over standard cylindrical wire arrays for driving hohlraums for inertial confinement fusion studies as the surface area of the electrodes in the load region (which serve as hohlraum walls) may be substantially reduced. In these experiments, mass and array width scans were performed using tungsten wires. A maximum total radiated x-ray power of 10±2 TW was observed with 20 mm wide arrays imploding in ∼100 ns at a load current of ∼3 MA, limited by the high inductance. Decreased power in the 4-6 TW range was observed at the smallest width studied (8 mm). 10 kJ of Al K-shell x-rays were obtained in one Al planar array fielded. This report will discuss the zero-dimensional calculations used to design the loads, the results of the experiments, and potential future research to determine if planar wire arrays will continue to scale favorably at current levels typical of the Z machine. Implosion dynamics will be discussed, including x-ray self-emission imaging used to infer the velocity of the implosion front and the potential role of trailing mass. Resistive heating has been previously cited as the cause for enhanced yields observed in excess of jxB-coupled energy. The analysis presented in this report suggests that jxBcoupled energy may explain as much as the energy in the first x-ray pulse but not the total yield, which is similar to our present understanding of cylindrical wire array behavior.4 Acknowledgment

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Section: Return Current Cagementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Planar wire array performance scaling at multi-MA levels on the Saturn generator.

Chuvatin

Jones²,

Vesey³

et al. 2007

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“…Inductive current division still allows current to be distributed throughout the wires in a planar array, but causes current to peak in the few wires near the edge of the array with the outermost wires carrying a factor of 2-3 times more current than the innermost wires [11]. We expect this to be the most reasonable assumption for planar arrays, given the observations that the inner wires ablate and so must carry some current [8], but also that the inner wires experience little acceleration while the implosion commences at the outer wires and cascades inward [11,13] implying that somewhat less current flows in the inner wires. Modeling with inductive division best reproduces the latter observation.…”

Section: Pre-shot 0d-type Modeling For Load Designmentioning

confidence: 99%

“…This could be a detrimental effect, leading to large MRT spatial broadening of the imploding mass, or it could be a positive effect leading to robust gap formation and high convergence in the MRT bubble regions. At the same time, the distributed mass in planar wire arrays is expected to help stabilize MRT growth during the implosion as the implosion front continues to snowplow wire material [11,12,13] (analogous to nested cylindrical arrays). It is not clear which of these effects will dominate the performance of planar wire arrays.…”

Section: Planar Wire Array Implosion Dynamicsmentioning

confidence: 99%

“…The planar array distributes the initial mass profile radially, which is not intuitively optimal for providing high implosion velocity. Numerical modeling [11,12] and laser shadowgraphy measurements [13] indicate, however, that the wires implode in a cascade, with magnetic Rayleigh-Taylor implosion instabilities being stabilized to some extent as the implosion front impacts each adjacent wire on its way toward the axis. This suggests that a linear array mitigates instabilities in a manner analogous to a multiply nested wire array; nested cylindrical wire arrays have been previously demonstrated to enhance the radiated x-ray power and shorten the pulse due to mitigation of the magnetic Rayleigh-Taylor (MRT) implosion instability [2] as the current is switched from the outer to the inner array during the implosion [14].…”

Section: Chapter 1 Introductionmentioning

confidence: 99%

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Compact wire array sources: power scaling and implosion physics.

Serrano¹,

Chuvatin

Jones³

et al. 2008

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A series of ten shots were performed on the Saturn generator in short pulse mode in order to study planar and small-diameter cylindrical tungsten wire arrays at ∼5 MA current levels and 50-60 ns implosion times as candidates for compact z-pinch radiation sources. A new vacuum hohlraum configuration has been proposed in which multiple z pinches are driven in parallel by a pulsed power generator. Each pinch resides in a separate return current cage, serving also as a primary hohlraum. A collection of such radiation sources surround a compact secondary hohlraum, which may potentially provide an attractive Planckian radiation source or house an inertial confinement fusion fuel capsule. Prior to studying this concept experimentally or numerically, advanced compact wire array loads must be developed and their scaling behavior understood. The 2008 Saturn planar array experiments extend the data set presented in Ref.[1], which studied planar arrays at ∼3 MA, 100 ns in Saturn long pulse mode. Planar wire array power and yield scaling studies now include current levels directly applicable to multi-pinch experiments that could be performed on the 25 MA Z machine. A maximum total x-ray power of 15 TW (250 kJ in the main pulse, 330 kJ total yield) was observed with a 12-mm-wide planar array at 5.3 MA, 52 ns. The full data set indicates power scaling that is sub-quadratic with load current, while total and main pulse yields are closer to quadratic; these trends are similar to observations of compact cylindrical tungsten arrays on Z. We continue the investigation of energy coupling in these short pulse Saturn experiments using zero-dimensional-type implosion modeling and pinhole imaging, indicating 16 cm/μs implosion velocity in a 12-mm-wide array. The same phenomena of significant trailing mass and evidence for resistive heating are observed at 5 MA as at 3 MA. 17 kJ of Al K-shell radiation was obtained in one Al planar array fielded at 5.5 MA, 57 ns and we compare this to cylindrical array results in the context of a K-shell yield scaling model. We have also performed an initial study of compact 3 mm diameter cylindrical wire arrays, which are alternate candidates for a multi-pinch vacuum hohlraum concept. These massive 3.4 and 6 mg/cm loads may have been impacted by opacity, producing a maximum x-ray power of 7 TW at 4.5 MA, 45 ns. Future research directions in compact x-ray sources are discussed. 4 AcknowledgmentWe thank M. Lopez (1675), G. T. Liefeste (1675), and J. L. Porter (1670) for providing load hardware and diagnostic support; L.B. Nielsen-Weber (1675) and D.S. Nielsen (1675) for extensive support of diagnostic installation, fielding, and film processing;

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Investigation of asymmetry of wire-array Z pinches at stagnation using a 4-channel laser diagnostic

Иванов

Anderson

2016

High Energy Density Physics

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Asymmetry of wire-array Z-pinches at stagnation was investigated using four synchronized laser beams at the wavelength of 266 nm. These beams were spaced at 45° with respect to each other, allowing a full view of the pinch from four directions. The laser pulse duration was 0.2 ns, with a <0.1 ns temporal accuracy between the four channels. Strong asymmetry was found in Z pinches produced by implosion of asymmetrical wire array loads. Anisotropy of the wire-array Z pinch arises due to the asymmetric implosion and development of plasma instabilities. Understanding the three-dimension structure of Z-pinches is important for interpretation of data from x-ray and laser diagnostics.

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Investigation of ablation and implosion dynamics in linear wire arrays

Cited by 20 publications

References 23 publications

Planar wire array performance scaling at multi-MA levels on the Saturn generator.

Planar wire array performance scaling at multi-MA levels on the Saturn generator.

Compact wire array sources: power scaling and implosion physics.

Investigation of asymmetry of wire-array Z pinches at stagnation using a 4-channel laser diagnostic

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