Imposed magnetic field and hot electron propagation in inertial fusion hohlraums

Strozzi, D. J.; Perkins, L.J.; Marinak, M. M.; Larson, David J.; Koning, J. M.; Logan, B.G.

doi:10.1017/s0022377815001348

Cited by 27 publications

(18 citation statements)

References 26 publications

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“…Previous work has considered the effect of an imposed field on capsule performance 4 and hohlraum conditions. 19 Simulations are performed using the radiation-hydrodynamics code HYDRA 20 both with and without MHD 21 included. Here, kinetic and nonlocal effects on heat transport are neglected.…”

Section: Introductionmentioning

confidence: 99%

Simulation of self-generated magnetic fields in an inertial fusion hohlraum environment

et al. 2017

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We present radiation-hydrodynamic simulations of self-generated magnetic field in a hohlraum, which show an increased temperature in large regions of the underdense fill. Non-parallel gradients in electron density and temperature in a laser-heated plasma give rise to a self-generated field by the “Biermann battery” mechanism. Here, HYDRA simulations of three hohlraum designs on the National Ignition Facility are reported, which use a partial magnetohydrodynamic (MHD) description that includes the self-generated source term, resistive dissipation, and advection of the field due to both the plasma flow and the Nernst term. Anisotropic electron heat conduction parallel and perpendicular to the field is included, but not the Righi-Leduc heat flux. The field strength is too small to compete significantly with plasma pressure, but affects plasma conditions by reducing electron heat conduction perpendicular to the field. Significant reductions in heat flux can occur, especially for high Z plasma, at modest values of the Hall parameter, Ωeτei≲1, where Ωe=eB/mec and τei is the electron-ion collision time. The inclusion of MHD in the simulations leads to 1 keV hotter electron temperatures in the laser entrance hole and high-Z wall blowoff, which reduces inverse-bremsstrahlung absorption of the laser beam. This improves propagation of the inner beams pointed at the hohlraum equator, resulting in a symmetry shift of the resulting capsule implosion towards a more prolate shape. The time of peak x-ray production in the capsule shifts later by only 70 ps (within experimental uncertainty), but a decomposition of the hotspot shape into Legendre moments indicates a shift of P2/P0 by ∼20%. This indicates that MHD cannot explain why simulated x-ray drive exceeds measured levels, but may be partially responsible for failures to correctly model the symmetry.

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Section: Introductionmentioning

confidence: 99%

Simulation of self-generated magnetic fields in an inertial fusion hohlraum environment

et al. 2017

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“…The MagnetoInertial Fusion Electric Discharge System has been developed to provide steady state magnetic fields for long time-scales relative to the experiments. An experiment on the Omega Laser Facility with a 7.5 T external axial magnetic field imposed on an Omega-scale hohlraum measured a rise in observed temperature along the hohlraum axis [5] and modeling showed that external fields can guide hot electrons from laser-plasma interactions [6] through the hohlraum, rather than the capsule [7]. From Ohm's Law, it has been shown that electron heat transport advects such magnetic fields through the Nernst effect [8][9][10][11][12][13][14] in addition to well-known processes like "frozen-in-flow" and resistive diffusion.…”

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confidence: 99%

“…Accurate modeling of these quantities has implications for laser plasma interactions [5,6] and hot electron propagation [7] in the gas fill and understanding hot spots on the dense plasma that generate X-rays. The kinetic electron transport and B field physics presented here could affect details of X-ray drive if incorporated into full-scale radiationhydrodynamics modeling (including reduced phenomenological laser-plasma interaction models) of indirect drive with externally applied B-field.…”

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confidence: 99%

Kinetic modeling of Nernst effect in magnetized hohlraums

et al. 2016

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We present nanosecond timescale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's Law, including Nernst advection of magnetic fields. In addition to showing the prevalence of non-local behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in-flux would suggest. Non-locality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling.There has been recent interest in the role of applied magnetic fields in high-energy-density plasmas [1-3] for inertial fusion energy applications [4]. The MagnetoInertial Fusion Electric Discharge System has been developed to provide steady state magnetic fields for long time-scales relative to the experiments. An experiment on the Omega Laser Facility with a 7.5 T external axial magnetic field imposed on an Omega-scale hohlraum measured a rise in observed temperature along the hohlraum axis [5] and modeling showed that external fields can guide hot electrons from laser-plasma interactions [6] through the hohlraum, rather than the capsule [7]. From Ohm's Law, it has been shown that electron heat transport advects such magnetic fields through the Nernst effect [8][9][10][11][12][13][14] in addition to well-known processes like "frozen-in-flow" and resistive diffusion. Dimensionless numbers comparing the ratio of the magnitudes of the Nernst term to the bulk plasma flow term, R N 1 [10], and the Hall term, H N 1 [13], suggest that Nernst convection should be the dominant mechanism for magnetic field transport in a hohlraum. Such a hot and semi-collisional environment is, however, rich in nonequilibrium effects that may complicate the magnetic field dynamics.Laser heating of the plasma results in steep temperature gradients, typically O(3 keV/50 µm). The collisional * archis@ucla.edu † agrt@umich.edu mean-free-path of a 3 keV electron is O(10 µm), depending on the plasma density. Since λ mfp /L < 100, nonlocality can be expected to be important [15]. The steep temperature gradients caused by intense laser heating in a hohlraum have been shown to result in non-local heat flow [16,17]. Careful consideration of the electron population with 2v th < v < 4v th is required as these carry most of the heat. Additionally, inverse-bremsstrahlung heating of a plasma [18,19] not only leads to deviations from Braginskii transport [20], but also new transport terms [21,22]. Both non-locality and laser heating result in modifications to the distribution function an...

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“…The prescribed 2-D time-dependent radiation drive asymmetry 14 is incorporated from the beginning of the drivephase. Magnetic field effects on the hohlraum (which can affect the radiation asymmetry 27,28 ) are not considered here. At 15.7 ns, which corresponds to the peak radiation temperature, the 2-D simulations are reconstructed into 3-D Cartesian for the stagnation phase.…”

Section: Simulation Setupmentioning

confidence: 99%

Perturbation modifications by pre-magnetisation of inertial confinement fusion implosions

et al. 2019

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Pre-magnetisation of inertial confinement fusion implosions on the National Ignition Facility has the potential to raise current high-performing targets into the ignition regime [Perkins et al. "The potential of imposed magnetic fields for enhancing ignition probability and fusion energy yield in indirect-drive inertial confinement fusion," Phys. Plasmas 24, 062708 (2017)]. A key concern with this method is that the application of a magnetic field inherently increases asymmetry. This paper uses 3-D extended-magnetohydrodynamics Gorgon simulations to investigate how thermal conduction suppression, the Lorentz force, and a-particle magnetisation affect three hot-spot perturbation scenarios: a cold fuel spike, a time-dependent radiation drive asymmetry, and a multi-mode perturbation. For moderate magnetisations (B 0 ¼ 5 T), the single spike penetrates deeper into the hot-spot, as thermal ablative stabilisation is reduced. However, at higher magnetisations (B 0 ¼ 50 T), magnetic tension acts to stabilise the spike. While magnetisation of a-particle orbits increases the peak hot-spot temperature, no impact on the perturbation penetration depth is observed. The P4-dominated radiation drive asymmetry demonstrates the anisotropic nature of the thermal ablative stabilisation modifications, with perturbations perpendicular to the magnetic field penetrating deeper and perturbations parallel to the field being preferentially stabilised by increased heat-flows. Moderate magnetisations also increase the prevalence of high modes, while magnetic tension reduces vorticity at the hot-spot edge for larger magnetisations. For a simulated high-foot experiment, the yield doubles through the application of a 50 T magnetic field-an amplification which is expected to be larger for higher-performing configurations.

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Imposed magnetic field and hot electron propagation in inertial fusion hohlraums

Cited by 27 publications

References 26 publications

Simulation of self-generated magnetic fields in an inertial fusion hohlraum environment

Simulation of self-generated magnetic fields in an inertial fusion hohlraum environment

Kinetic modeling of Nernst effect in magnetized hohlraums

Perturbation modifications by pre-magnetisation of inertial confinement fusion implosions

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