Hot electron measurements in ignition relevant <i>Hohlraums</i> on the National Ignition Facility

Dewald, E. L.; Thomas, C. A.; Hunter, Steve L.; Divol, L.; Meezan, N. B.; Glenzer, S. H.; Suter, L. J.; Bond, E.; Kline, J. L.; Celeste, J.; Bradley, D. K.; Bell, P. M.; Kauffman, R. L.; Kilkenny, J. D.; Landen, O. L.

doi:10.1063/1.3478683

Cited by 61 publications

(39 citation statements)

References 10 publications

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“…The electron distribution is calculated from the measurement of the Bremsstrahlung hard x-ray emitted through the hohlraum wall by energetics electrons with the FFLEX diagnostic [18][19][20]. The 10 FFLEX channels are absolutely calibrated, and their spectral responses include the detailed hohlraum composition (gold wall and aluminum case).…”

Section: Inferring Srs On the 235 • Conementioning

confidence: 99%

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Michel¹,

Divol²,

Town³

et al. 2011

Phys. Rev. E

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By using three tunable wavelengths on different cones of laser beams on the National Ignition Facility, numerical simulations show that the energy transfer between beams can be tuned to redistribute the energy within the cones of beams most prone to backscatter instabilities. These radiative hydrodynamics and laser-plasma interaction simulations have been tested against large scale hohlraum experiments with two tunable wavelengths, and reproduce the hohlraum energetics and symmetry. Using a third wavelength provides a greater level of control of the laser energy distribution and coupling in the hohlraum, and could significantly reduce stimulated Raman scattering losses and increase the hohlraum radiation drive while maintaining a good implosion symmetry.

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Section: Inferring Srs On the 235 • Conementioning

confidence: 99%

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Michel¹,

Divol²,

Town³

et al. 2011

Phys. Rev. E

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“…Hot electron populations in NIF hohlraums are inferred by hard x-ray measurements made with the FFLEX diagnostic [61,62]. The data suggests two hot electron populations with distinct temperatures of ∼18 and ∼100 keV.…”

Section: Simulations Including Hot Electron Pre-heatmentioning

confidence: 99%

Capsule modeling of high foot implosion experiments on the National Ignition Facility

Clark

Kritcher

Milovich

et al. 2017

Plasma Phys. Control. Fusion

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This paper summarizes the results of detailed, capsule-only simulations of a set of high foot implosion experiments conducted on the National Ignition Facility (NIF). These experiments span a range of ablator thicknesses, laser powers, and laser energies, and modeling these experiments as a set is important to assess whether the simulation model can reproduce the trends seen experimentally as the implosion parameters were varied. Two-dimensional (2D) simulations have been run including a number of effects-both nominal and off-nominal-such as hohlraum radiation asymmetries, surface roughness, the capsule support tent, and hot electron pre-heat. Selected three-dimensional simulations have also been run to assess the validity of the 2D axisymmetric approximation. As a composite, these simulations represent the current state of understanding of NIF high foot implosion performance using the best and most detailed computational model available. While the most detailed simulations show approximate agreement with the experimental data, it is evident that the model remains incomplete and further refinements are needed. Nevertheless, avenues for improved performance are clearly indicated.

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“…These energetic electrons are believed to be generated through two-plasmon decay [31] and stimulated Raman scattering in gas-filled hohlraums and may degrade implosion performance of a cryogenic fuel layer by decompressing the fuel [32]. The Filter-Fluorescer Experiment (FFLEX) diagnostic measures hard x-ray bremsstrahlung emission over specific energy bands and is used to infer suprathermal electron generation [33]. A conventional gas-filled hohlraum with a 1.2 MJ (4-shock) drive generated nearly 1 kJ of suprathermal electrons; in comparison, 1.2 MJ (2-shock) drive in the NVH generated approximately 10 J. Suprathermal electrons also introduce a high background on diagnostics, limiting measurement capabilities; the low x-ray background of the NVH improves signal measurements, presenting new implosion diagnostic opportunities, for example with Compton radiography or proton time-of-flight detectors [34] to measure fuel-ablator density variations.…”

Section: Fig 2 (Color Online) (A)mentioning

confidence: 99%

First High-Convergence Cryogenic Implosion in a Near-Vacuum Hohlraum

Hopkins¹,

Meezan²,

Pape³

et al. 2015

Phys. Rev. Lett.

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124

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Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ∼ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 × 10 15 neutrons, with 20% calculated alpha heating at convergence ∼27×. Inertial confinement fusion (ICF) experiments implode millimeter-scale deuterium-tritium (DT) filled spherical capsules, compressing and heating the DT fuel to fusion conditions and releasing energy [1]. Indirect-drive ICF places the fuel-filled capsule at the center of a high-Z radiation enclosure (hohlraum) and strikes the inside walls of the hohlraum with laser power. This produces an internal bath of x rays-a radiation drive which ablates and implodes the fuel-filled capsule. The National Ignition Facility (NIF) [2,3] drives this process using 192 frequency-tripled laser beams (351 nm at 3ω), which enter a cylindrical hohlraum through laser entrance holes (LEHs) at each end. The laser beams are pointed through the LEHs to provide various angles of drive to the capsule such that the superposition of drives can be spherically symmetric throughout the implosion time.Typically, ICF experiments on the NIF have utilized plastic (CH) capsules inside gold hohlraums filled with helium at densities ranging from 0.96 [4] to 1.6 mg=cm Although vacuum hohlraums were initially considered, the long pulse duration for CH capsules led to choosing higher densities of hohlraum fill [7,8] to minimize expansion of the interior gold wall [ Fig. 1(a)] [9]. The intended effect is to maintain an open path for laser propagation to the wall for the full pulse duration.In this Letter, we report on the first experimental campaign on the NIF using near-vacuum hohlraums (NVH) to drive a high convergence cryogenic DT layered capsule implosion. A NVH has a hohlraum fill density of 0.03 mg=cm 3 helium, more than an order of magnitude lower density than conventional gas-filled hohlraums (0.96-1.6 mg=cm 3 ). Symmetry of implosions driven with the NVH is controlled through direct adjustments to the inner and outer beam power balance rather than relying on beam wavelength separations [10] and the resultant crossbeam energy transfer [11,12]. Unlike earlier research on true "vacuum" hohlraums [13][14][15], the NVH...

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Hot electron measurements in ignition relevant Hohlraums on the National Ignition Facility

Cited by 61 publications

References 10 publications

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Capsule modeling of high foot implosion experiments on the National Ignition Facility

First High-Convergence Cryogenic Implosion in a Near-Vacuum Hohlraum

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