The ten long-pulse laser beams of the Orion facility have been considered as a direct driver for the irradiation of a spherical capsule. The intrinsic root-mean-square illumination non-uniformity
σ
0
...has been evaluated assuming circular and elliptical super-Gaussian laser intensity profiles. Calculations accounting for nominal uncertainties in power imbalance, pointing error and target positioning have shown a degradation of the irradiation uniformity. Non-uniformity of the irradiation as a function of the capsule radius has been calculated and it has been shown that the use of the polar direct drive technique significantly improves the quality of the irradiation. Finally, it is found that an elliptical focal shape provides better symmetry results in comparison to circular ones, whilst the laser-capsule coupling is reduced.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
An axially symmetric laser beam configuration irradiating a spherical capsule has been considered in the context of inertial confinement fusion (ICF). The laser beams are located at co-latitudes 49° ...and 131° and mimic the quad positions in the second cone of the Laser Mégajoule Facility. The capsule is directly irradiated by the laser beams whose energy deposition generates a nearly spherical shock wave. Two-dimensional hydrodynamic numerical simulations have been performed to analyse the non-uniformity of the shock wavefront launched inward throughout the target. Different laser intensity profiles, calculated by the illumination model, have been tested. The performance, in terms of shock non-uniformity, has been compared, and it is found that with an appropriate choice of the laser intensity profile it is possible to control the shock non-uniformity at early times.
Three-dimensional (3D) hydrodynamic numerical simulations of laser driven thin-shell gas-filled microballoons have been carried out using the computer code MULTI-3D Ramis et al., Phys. Plasmas 21, ...082710 (2014). The studied configuration corresponds to experiments carried at the ORION laser facility Hopps et al., Plasma Phys. Controlled Fusion 57, 064002 (2015). The MULTI-3D code solves single-temperature hydrodynamics, electron heat transport, and 3D ray tracing with inverse bremsstrahlung absorption on unstructured Lagrangian grids. Special emphasis has been placed on the genuine 3D effects that are inaccessible to calculations using simplified 1D or 2D geometries. These include the consequences of (i) a finite number of laser beams (10 in the experimental campaign), (ii) intensity irregularities in the beam cross-sectional profiles, (iii) laser beam misalignments, and (iv) power imbalance between beams. The consequences of these imperfections have been quantified by post-processing the numerical results in terms of capsule nonuniformities (synthetic emission and absorption images) and implosion efficiency (convergence ratio and neutron yield). Statistical analysis of these outcomes allows determination of the laser tolerances that guarantee a given level of target performance.
Inertial confinement fusion: a defence context Randewich, Andrew; Lock, Rob; Garbett, Warren ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
11/2020, Volume:
378, Issue:
2184
Journal Article
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
7.
Inertial confinement fusion Randewich, Andrew; Lock, Rob; Garbett, Warren ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
11/2020, Volume:
378, Issue:
2184
Journal Article
Abstract
The use of the Laser MegaJoule facility within the shock ignition scheme has been considered. In the first part of the study, one-dimensional hydrodynamic calculations were performed for an ...inertial confinement fusion capsule in the context of the shock ignition scheme providing the energy gain and an estimation of the increase of the peak power due to the reduction of the photon penetration expected during the high-intensity spike pulse. In the second part, we considered a Laser MegaJoule configuration consisting of 176 laser beams that have been grouped providing two different irradiation schemes. In this configuration the maximum available energy and power are 1.3 MJ and 440 TW. Optimization of the laser–capsule parameters that minimize the irradiation non-uniformity during the first few ns of the foot pulse has been performed. The calculations take into account the specific elliptical laser intensity profile provided at the Laser MegaJoule and the expected beam uncertainties. A significant improvement of the illumination uniformity provided by the polar direct drive technique has been demonstrated. Three-dimensional hydrodynamic calculations have been performed in order to analyse the magnitude of the azimuthal component of the irradiation that is neglected in two-dimensional hydrodynamic simulations.
A direct-drive shock ignition scheme in the context of the Laser MegaJoule facility has been considered. The irradiation uniformity provided by two laser beam configurations using a total of 10 or 20 ...quads to drive the first compression phase has been analyzed. Firstly, a numerical method is used to optimize the laser intensity profiles in the context of the illumination approximation model; then these profiles are used to calculate the irradiation non-uniformity of a spherical target of radius
r
0
= 1000
μ
m assuming the beam uncertainties: power imbalance 5%, pointing error 50
μ
m and target positioning 20
μ
m. These uncertainties deteriorate the quality of the irradiation increasing considerably the irradiation non-uniformity; moreover, it is found that the pointing error provides the major contribution to the degradation of the irradiation. A strategy to mitigate the negative effect induced by the beam uncertainties is proposed. It consists in using a composite profile in each beam: a first large and flat intensity profile provides a background that reduces pointing error and target positioning effects, whilst a second overlapping profile optimizes the illumination irradiation. It is found that the introduction of the flat background with an intensity of 55% with respect to the maximum intensity reduces by about 40% the non-uniformity of the irradiation due to beam uncertainties.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Predicting and matching radiation wave propagation with computational models has proven difficult. Information provided by experiments studying radiation flow has been limited when only radiation ...breakout is measured. We have developed the COAX (co-axial) diagnostic platform to provide spatial temperature profiles of a radiation wave through low density foams as a more detailed constraint for simulations. COAX uses a standard, laser-driven OMEGA-60 halfraum to drive radiation down a titanium-laden silicon oxide foam. Point-projection X-ray absorption spectroscopy perpendicular to the radiation flow measures the spatial profile of titanium ionization. The spectroscopic measurement utilizes a broadband capsule backlighter. Imaging and streak spectroscopy are used to characterize the size and spectrum of this source. Radiography provides an additional constraint by capturing the developing shock as the radiation flow becomes subsonic. The DANTE diagnostic is used to measure the halfraum temperature. We provide a spectroscopic analysis of COAX data to determine temperature, and we describe experimental sources of uncertainty. The temperature is obtained by comparison to multi-temperature synthetic spectra post-processed from radiation-hydrodynamics simulations. Quantitative comparison between data and synthetic spectra generated from temperature profiles at relevant simulation times enable determination of a peak temperature of 114 ± 8 eV at 265 ± 22.4 μm from the halfraum. This represents an improvement over the temperature uncertainties of previous radiation flow experiments. Further refinements to the spectroscopic analysis could achieve ± 4 eV. The combination between space-resolved spectroscopy and radiography enables us to determine the distance from the halfraum of both the radiation front and the shock front at the time of measurement. For the example shown in this paper the radiation front position is 600–630 μm at 3.43 ± 0.16 ns and the shock front position is 633 μm at 3.3 ± 0.24 ns.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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