339 research outputs found
Modified parameterization of the Li-Petrasso charged-particle stopping power theory
No full textCharged-particle energy loss or “stopping power” in plasmas has been studied theoretically and experimentally, with important applications in modeling fusion experiments. Dense plasmas relevant to inertial fusion are theoretically challenging, but several models have been developed. Here, we report several physically motivated modifications to the parameterization of the Li-Petrasso stopping-power model. The new parameterization described in this work leads to larger discrepancies between the Li-Petrasso model and both other theories and experi- mental data near the Bragg peak for plasma stopping, corroborating recent conclusions that the Li-Petrasso model is not accurate in this regime [Frenje et al., Phys. Rev. Lett. 122, 015002 (2019)]. Conversely, our modified parameterization agrees better with other theories in the high-velocity limit
Electron-ion thermal equilibration after spherical shock collapse
No full textA comprehensive set of dual nuclear product observations provides a snapshot of imploding inertial confinement fusion capsules at the time of shock collapse, shortly before the final stages of compression. The collapse of strong convergent shocks at the center of spherical capsules filled with D[subscript 2] and [subscript 3]He gases induces D-D and D-[superscript 3]He nuclear production. Temporal and spectral diagnostics of products from both reactions are used to measure shock timing, temperature, and capsule areal density. The density and temperature inferred from these measurements are used to estimate the electron-ion thermal coupling and demonstrate a lower electron-ion relaxation rate for capsules with lower initial gas density.New York State Energy Research and Development AuthorityDepartment of EnergyLaboratory for Laser EnergeticsDepartment of Energy Office of Inertial Confinement Fusio
Numerical simulation of exploding pusher targets
No full textExploding pusher targets, i.e. gas-filled large aspect-ratio glass or plastic shells, driven by a strong laser- generated shock, are widely used as pulsed sources of neutrons and fast charged particles. Recent experiments on exploding pushers provided evidence for the transition from a purely fluid behavior to a kinetic one [1]. Indeed, fluid models largely overpredict yield and temperature as the Knudsen number Kn (ratio of ion mean-free path to compressed gas radius) is comparable or larger than one. At Kn = 0.3 - 1, fluid codes reasonably estimate integral quantities as yield and neutron-averaged temperatures, but do not reproduce burn radii, burn profiles and DD/DHe3 yield ratio. This motivated a detailed simulation study of intermediate-Kn exploding pushers. We will show how simulation results depend on models for laser- interaction, electron conductivity (flux-limited local vs nonlocal), viscosity (physical vs artificial), and ion mixing.
∗Work partially supported by Sapienza Project C26A15YTMA, Sapienza 2016 (n. 257584), and Eurofusion Project AWP17-ENR- IFE-CEA-01
Ion-kinetic simulation of D-3He gas-filled ICF target implosions with moderate to large Knudsen number
No full textExperiments designed to investigate the transition to non-collisional behavior in D3He-gas ICF target implo- sions display increasingly large discrepancies with respect to simulations by standard hydrodynamics codes as the expected ion mean-free-paths λc increase with respect to the target radius R (i.e. when the Knudsen number NK = λc/R grows). To take properly into account large NK’s, multi-ion-species Vlasov-Fokker- Planck computations of the inner gas in those capsules have been performed, for two different values of NK, one moderate and one large. The results, including nuclear yield, reactivity-weighted ion temperatures, nu- clear emissivities and surface brightness, have been compared with experimental data and with the results of hydrodynamical simulations, some of which include an ad-hoc modeling of kinetic effects. The experimental results are quite accurately rendered by the kinetic calculations in the smaller-NK case, much better than by the hydrodynamical calculations. The kinetic effects at play in that case are thus correctly understood. However, in the higher-NK case, the agreement is much worse. The remaining discrepancies are shown to arise from kinetic phenomena (e.g., inter-species diffusion) occurring at the gas-pusher interface, which should be investigated in future work
Fusion Yield Enhancement in Magnetized Laser-Driven Implosions
No full textEnhancement of the ion temperature and fusion yield has been observed in magnetized laser-driven inertial confinement fusion implosions on the OMEGA Laser Facility. A spherical CH target with a 10 atm D[subscript 2] gas fill was imploded in a polar-drive configuration. A magnetic field of 80 kG was embedded in the target and was subsequently trapped and compressed by the imploding conductive plasma. As a result of the hot-spot magnetization, the electron radial heat losses were suppressed and the observed ion temperature and neutron yield were enhanced by 15% and 30%, respectively.United States. Dept. of Energy (Cooperative Agreement No. DE-FC02-04ER54789)United States. Dept. of Energy (Cooperative Agreement No. DE-FC03-92SF19460
Investigation of the transition between hydrodynamic and kinetic regimes for DT exploding pushers at OMEGA and the NIF
No full textPrevious experiments were conducted to
study the transition from hydrodynamic-like to ion kinetic regimes
for D3He exploding pushers [1], demonstrating the importance of an
ion kinetic approach for formulating more robust predictions of implosion
characteristics. This presentation details a series of planned
experiments at the OMEGA Facility and the NIF using thin-glass
exploding pushers with DT fuel. D and T ions have the same charge,
unlike D and 3He, yet their masses are unaltered from the D and
3He case. This allows for the investigation of whether ion-thermal
decoupling and species separation are largely a result of charge or
mass. [2] The initial gas fill pressure will be varied in order to scan
the transition from strongly hydrodynamic to strongly kinetic implosions,
while leveraging the expansive diagnostic suite developed
at NIF and OMEGA.∗This work was supported in part by LLE, the U.S. DoE (NNSA,
NLUF) and LLNL.
1M. Rosenberg et al., Phys. Rev. Lett. 112, 185001.
2H. Rinderknecht et al., Phys. Rev. Lett. 114, 025001
Plasma-Density Determination from X-Ray Radiography of Laser-Driven Spherical Implosions
No full textThe fuel layer density of an imploding laser-driven spherical shell is inferred from framed x-ray radiographs. The density distribution is determined by using Abel inversion to compute the radial distribution of the opacity κ from the observed optical depth τ. With the additional assumption of the mass of the remaining fuel, the absolute density distribution is determined. This is demonstrated on the OMEGA laser system with two x-ray backlighters of different mean energies that lead to the same inferred density distribution independent of backlighter energy.New York State Energy Research and Development AuthorityUniversity of RochesterU.S. Department of Energy, Office of Inertial Confinement Fusion (Cooperative Agreement No. DE-FC52-08NA28302
Pressure-driven, resistive magnetohydrodynamic interchange instabilities in laser-produced high-energy-density plasmas
No full textRecent experiments using proton backlighting of laser-foil interactions provide unique opportunities for studying magnetized plasma instabilities in laser-produced high-energy-density plasmas. Time-gated proton radiograph images indicate that the outer structure of a magnetic field entrained in a hemispherical plasma bubble becomes distinctly asymmetric after the laser turns off. It is shown that this asymmetry is a consequence of pressure-driven, resistive magnetohydrodynamic (MHD) interchange instabilities. In contrast to the predictions made by ideal MHD theory, the increasing plasma resistivity after laser turn-off allows for greater low-mode destabilization (m>1) from reduced stabilization by field-line bending. For laser-generated plasmas presented herein, a mode-number cutoff for stabilization of perturbations with m>∼[8πβ(1+D[subscript m]k⊥(2)γmax(−1))](1/2) is found in the linear growth regime. The growth is measured and is found to be in reasonable agreement with model predictions.University of Rochester Fusion Science CenterLaboratory for Laser EnergeticsLawrence Livermore National LaboratoryDepartment of Energ
Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas
No full textThe demonstration of magnetic field compression to many tens of megagauss in cylindrical implosions of inertial confinement fusion targets is reported for the first time. The OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with a strong external field (>50 kG) from a specially developed magnetic pulse generator. This seed field was trapped (frozen) in the shock-heated gas fill and compressed by the imploding shell at a high implosion velocity, minimizing the effect of resistive flux diffusion. The magnetic fields in the compressed core were probed via proton deflectrometry using the fusion products from an imploding D[subscript 3]He target. Line-averaged magnetic fields between 30 and 40 MG were observed.New York State Energy Research and Development AuthorityUniversity of RochesterU.S. Department of Energy (Grant No. DE-FG02-04ER54768 and Cooperative Agreement Nos. DE-FC02-ER54789 and DE-FC52- 08NA28302,
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