Yield reduction via the Knudsen layer effect in a mixture of fuel and pusher material

McDevitt, Christopher J.; Tang, Xian-Zhu; Guo, Zehua

doi:10.1088/1361-6587/aaee5a

Cited by 3 publications

(2 citation statements)

References 47 publications

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“…In the early phase, about few hundred pico-seconds after the laser ablation, the density of the converged plasmas at the center of the hohlraum is quite low. The Knudsen number (N k is defined as the ratio of ion mean-free-path to minimum target radius) is large enough for the ions to move freely in the converged plasmas [39,[40][41][42][43][44]. Part of the neutrons are emitted based on the kinetic effect (beam-thermal and beam-beam reactions), and contribute a pseudo high ion temperature derived from the measured neutron time-of-flight (nTOF) spectrum.…”

Section: The Principle and Schematic Of Scpfmentioning

confidence: 99%

The investigation of spherically convergent plasma fusion as a high-flux neutron source with a long-pulsed laser driving

Yan¹,

Ren²,

Chen³

et al. 2022

Nucl. Fusion

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The spherically convergent plasma fusion (SCPF) scheme is a robust approach to provide a high-brightness pulsed neutron source. The performance of the SCPF driven by the long-pulsed laser is investigated. The experiments, with the laser pulse duration in a range of 0.5ns to 3ns, were implemented on ShenGuang-II Upgrade facility and a 100kJ level laser facility. The intensity of the laser beam was about multiple 1014W/cm2. The measured D-D reaction neutron yields were in a range of 7.3×108 to 1.01×1011, while the driven laser energies were in a range of 2.1kJ to 100.5kJ. The temporal self-emitted X-ray flux and image were measured. They shew that the plasma core could be maintained for a longer time in the long duration shots. The neutron reaction rate was measured on the 100kJ level laser facility. The full width at half maximum (FWHM) reached about 1ns in the shot with 2ns duration laser. The scaling law of the measured yields respect to the laser power and the pulse duration were presented. The neutron yield was possible to be increased by increasing the power and extending the duration.

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Section: The Principle and Schematic Of Scpfmentioning

confidence: 99%

The investigation of spherically convergent plasma fusion as a high-flux neutron source with a long-pulsed laser driving

Yan¹,

Ren²,

Chen³

et al. 2022

Nucl. Fusion

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“…A more detailed discussion that clarifies the various compensating effects due to disparate plasma temperatures for pusher and fuel remnants, which involves a detailed collisional-radiative modeling, is given in a followup paper [29]. It is also interesting to note that although this letter uses gold pusher for quantitative illustration, the effect of a plastic pusher on fusion yield, albeit in simplified feature geometries of what one can expect from Rayleigh-Taylor mix, has been recently quantified by solving the tail ion Fokker-Planck equation [30] using the fluid-kinetic hybrid formulation [22]. Further works to quantify this effect on fusion yield in specific implosion platforms are hopefully motivated by the physics explained here.…”

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confidence: 99%

Diffusive tunneling of Gamow fuel ions in a mixture of fusion fuel and inert pusher

Tang¹,

Elder²,

McDevitt³

et al. 2018

EPL

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Hydrodynamic mix produces small features for inter-mixed deuterium-tritium fuel and inert pusher materials. The dynamical reduction of size for the fuel cells that are segmented by pusher layers lead to greater local Knudsen numbers, which tend to aggravate the Knudsen layer fusion reactivity reduction. While the increasing yield reduction with increasing Knudsen number of the fuel region is straightforwardly anticipated, we show that once the pusher materials is stretched sufficiently thin by hydrodynamic mix, the fast fuel ions diffusively tunnel through them with minimal energy loss, so the Knudsen layer yield reduction becomes alleviated. This yield recovery can occur in a chunk-mixed plasma, significantly before the far more stringent, asymptotic limit of an atomically homogenized fuel and pusher assembly.

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Diffusive tunneling in an isobaric but non-isothermal fuel-pusher mixture

et al. 2019

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The hydrodynamic mix of fusion fuel and inert pusher can simultaneously generate smaller fuel pockets and finer pusher layers that separate them. Smaller fuel pockets have greater local Knudsen numbers, which tend to exacerbate the Knudsen layer reactivity reduction. A thinner pusher layer separating the neighboring fuel pockets, on the other hand, can enable the diffusive tunneling of Gamow fuel ions through the pusher layer and hence alleviate the Knudsen layer reactivity degradation. Here, the diffusive tunneling phenomenon describes a random walk process by which the Gamow fuel ions from one fuel pocket can traverse the inert pusher layer to join a neighboring fuel pocket without losing much of their energy. This is made possible by the much slower collisional slowing down rate compared with the pitch angle scattering rate of light fuel ions with heavier pusher ions. In an isobaric target mixture where fuel and pusher segments can have distinct temperatures, due to their different compressibilities, the temperature effect on the critical pusher layer areal density below which diffusive tunneling can occur, which is a property of the hydrodynamic mix, is understood by computing the ion charge state distribution using a collisional radiative model. This information is fed into the collisionality evaluation, enabling a parametric scan of the diffusive tunneling physics in terms of the target pressure, fuel, and pusher temperatures. It is found that when the gold pusher layer has a temperature above 1 keV, the variation of the pusher temperature has little effect on the critical areal mass density below which diffusive tunneling can occur. If the pusher layer is 1 keV or below, the critical areal mass density rises sharply, indicating that for a stronger fuel-pusher temperature disparity, the onset of diffusive tunneling will be at an earlier stage of the hydrodynamic mix when the fuel-pusher mixing structures are of less reduced size.

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Yield reduction via the Knudsen layer effect in a mixture of fuel and pusher material

Cited by 3 publications

References 47 publications

The investigation of spherically convergent plasma fusion as a high-flux neutron source with a long-pulsed laser driving

The investigation of spherically convergent plasma fusion as a high-flux neutron source with a long-pulsed laser driving

Diffusive tunneling of Gamow fuel ions in a mixture of fusion fuel and inert pusher

Diffusive tunneling in an isobaric but non-isothermal fuel-pusher mixture

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