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Glebov, V. Yu.

Publications and source records attributed to Glebov, V. Yu..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

3D xRAGE simulation of inertial confinement fusion implosion with imposed mode 2 laser drive asymmetry

Low-mode asymmetries represent an important obstacle to achieving high-gain inertial confinement fusion implosions. As a step in learning how to control such effects, an OMEGA experiment with imposed mode 2 laser drive asymmetries was done to study the expected signatures of this type of asymmetry [M. Gatu Johnson et al., PRE 2018]. In the present work, a 3D xRAGE simulation including the stalk mount has been brought to bear on the data from that experiment. Furthermore, comprehensive comparisons between simulated and measured observables are made. Good agreement between simulated and measured x-ray image-inferred shell trajectories, bang times and neutron emission widths are seen, showing that the hydrodynamics are well captured in the simulation. Asymmetries seen in simulated and measured time-resolved and time-integrated x-ray images and areal densities also compare well, showing impact of both stalk and mode 2. On the other hand, important differences in measured and simulated neutron emission histories, yield, and ion temperature (T ion ) asymmetries are seen, suggesting that the simulation is overestimating shock yield. Overall, the results clearly demonstrate the importance of considering all asymmetry sources when interpreting measured signatures of asymmetry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

2 H(p,γ) 3 He cross section measurement using high-energy-density plasmas

An absolute cross section for the radiative capture reaction 2 H(p,γ) 3 He has been measured at the OMEGA laser facility using inertially confined plasmas. These high-temperature plasmas are created by imploding a fuel-containing capsule using laser ablation, and are advantageous in that they better mimic astrophysical systems. We measure an S factor for this reaction of 0.429 ± 0.026 stat ± 0.072 sys eV b at E c.m . = 16.35 ± 0.40 keV, which is higher than the adopted evaluations. Furthermore, this reaction is important as a source of nuclear energy in protostars and brown dwarfs. It is also a critical reaction during big-bang nucleosynthesis, and an accurate cross section can be used as a constraint on cosmology.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

A suite of neutron time-of-flight detectors to measure hot-spot motion in direct-drive inertial confinement fusion experiments on OMEGA

A suite of six neutron time of flight detectors capable of measuring the primary DT neutron energy spectrum has recently been completed on the OMEGA Laser System. The detectors are positioned along multiple quasi-orthogonal lines of sight (LOS’s) in either a stand-alone, collinear, or antipodal configuration. The collinear detector configuration enables one to measure the neutron velocity along the detector LOS independent of the neutron-production history, while the antipodal detector configuration enables one to directly measure of the hot-spot velocity along the detector axis and Gamow velocity shift due to the plasma ion temperature. Using these six measurements of the primary DT neutron energy spectrum, the neutron-averaged hot-spot velocity and Gamow velocity shift of DT fusion neutrons have been measured in cryogenic experiments on OMEGA for the first time. Finally, the detector suite is operable between DT neutron yields of 1 × 10 13 to 2 × 10 14 with an uncertainty of ~14 km/s in the neutron-averaged hot-spot velocity measurement.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Impact of stalk on directly driven inertial confinement fusion implosions

Low-mode asymmetries have emerged as one of the primary challenges to achieving high-performing inertial confinement fusion (ICF) implosions. In direct-drive ICF, an important potential seed of such asymmetries is the capsule stalk mount, the impact of which has remained a contentious question. In this paper, we describe the results from an experiment on the OMEGA laser with intentional offsets at varying angles to the capsule stalk mount, which clearly demonstrates the impact of the stalk mount on implosion dynamics. The angle between stalk and offset is found to significantly impact observables. Specifically, a larger directional flow is observed in neutron spectrum measurements when the offset is toward rather than away from the stalk, while an offset at 42° to the stalk gives minimal directional flow but still generates a large flow field in the implosion. No significant directional flow is seen due to stalk only. Time-integrated x-ray images support these flow observations. A trend is also seen in implosion yield, with lower yield obtained for offsets with a smaller angle than with a larger angle toward the stalk. Radiation hydrodynamic simulations using 2D DRACO and 2D/3D Chimera not including the stalk mount and using 2D xRAGE including the stalk mount are brought to bear on the data. The yield trend, the minimal directional flow with stalk only, and the larger flow enhancement observed with the offset toward the stalk are all reproduced in the xRAGE simulations. Finally, the results strongly indicate that the stalk impact must be considered and mitigated to achieve high-performing implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Response of a lead-free borosilicate-glass microchannel plate to 14-MeV neutrons and γ-rays

In microchannel plate applications, such as in space telescopes, night-vision devices, or time-of-flight particle detection, reducing the sensitivity to signals from background sources, such as γ-rays, is beneficial for the system design and performance. The response of a single-stage lead-free borosilicate-glass microchannel plate to 14-MeV neutrons and γ-rays produced via (n, γ) reactions in surrounding structures was investigated at OMEGA. The average efficiency values for secondary electron production were found to be (5.1 ± 0.7) × 10−3 for 14-MeV neutrons and (4.9 ± 1.1) × 10−3 for ⟨1.5⟩-MeV γ-rays.

Parker, C. E. (ORCID:0000000303626984)↗
DOE OSTI2019

Deuteron breakup induced by 14-MeV neutrons from inertial confinement fusion

Measurements are reported for the angle-averaged double-differential cross section $\langle$d 2 σ/dE n dΩ n $\rangle$ 0°< θ < 7.4° for the breakup reaction 2 H ($n,2n$) 1 H, induced by 14-MeV neutrons generated using an inertial confinement fusion platform. A bright neutron source, created on the OMEGA Laser System [Boehly et al., Opt. Commun. 133, 495 (1997)] with a luminosity of L = 10 24 s -1 , was used to irradiate deuterated targets. The absolute yields and energy spectra from the breakup neutrons emitted in a forward-angle geometry (θ = 0° to 7.4°) were detected with a sensitive, high-dynamic-range neutron time-of-flight spectrometer. The cross-section data, measured for neutron energy range from 0.5 to 10 MeV, is well reproduced by a theoretical calculation employing realistic nucleon–nucleon and three-nucleon forces.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Fuel-shell interface instability growth effects on the performance of room temperature direct-drive implosions

Performance degradation in direct-drive inertial confinement fusion implosions is caused by several effects, one of which is Rayleigh-Taylor (RT) instability growth during the deceleration phase. In room-temperature plastic target implosions, deceleration-phase RT growth is enhanced by the density discontinuity and finite Atwood number at the fuel-shell interface. In this paper, the Atwood number of the interface is systematically varied by altering the ratio of deuterium to tritium (D:T) within the DT gas fill. It is shown that the stability of the interface is best characterized by the effective Atwood number, which is primarily determined by radiation heating of the shell and not by the composition of the fuel. Both simulation and experimental data show that yield performance scales with the fraction of D and T present in the fuel and that the observed inferred ion temperature asymmetry $(ΔT_i = T_i^{max} - T_i^{min})$, which indicates the presence of long-wavelength modes, has a small sensitivity to the different D:T ratios.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

A platform for nuclear physics experiments with laser-accelerated light ions

A novel platform for nuclear physics experiments has been observed on the high-energy, short-pulse OMEGA EP Laser System. Planar foil targets are irradiated with a 10-ps, 1-kJ infrared beam focused to an intensity of the order of 10 18 W/cm 2 . Relativistic electrons generated in the laser–target interaction escape the target, generating a very large electrostatic field, which extracts ions from the target’s back surface and accelerates them to MeV energies. The energetic ion flow from the back side of this primary target creates neutrons and charged particles through nuclear reactions in a secondary target placed in the ion flow. Charged-particle detectors were used to measure the energy spectra of the ions. The energy spectrum of the neutrons generated in the secondary target was measured using scintillator-based neutron time-of-flight detectors. First experiments to confirm the performance of this setup studied d(d,n) 3 He and 9 Be(d,n) 10 B reactions. This experimental platform is suitable especially for survey-type studies of nuclear reactions and for reactions that involve rare or radioactive ions like tritium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Impact of imposed mode 2 laser drive asymmetry on inertial confinement fusion implosions

Low-mode asymmetries have emerged as one of the primary challenges to achieving high-performing inertial confinement fusion implosions. These asymmetries seed flows in the implosions, which will manifest as modifications to the measured ion temperature (Tion) as inferred from the broadening of primary neutron spectra. The effects are important to understand both to learn to control and mitigate low-mode asymmetries, and to experimentally more closely capture thermal Tion used as input in implosion performance metric calculations. In this paper, results from and simulations of a set of experiments with a seeded mode 2 in the laser drive are described. The goal of this intentionally asymmetrically driven experiment was to test our capability to predict and measure the signatures of flows seeded by the low-mode asymmetry. The results from these experiments (first discussed in M Gatu Johnson et al, Phys. Rev. E 98, 051201(R) (2018)) demonstrate the importance of interplay of flows seeded by various asymmetry seeds. In particular, measured Tion and self-emission x-ray asymmetries are expected to be well captured by interplay between flow seeded by the imposed mode 2 and the capsule stalk mount. Measurements of areal density asymmetry also indicate the importance of the stalk mount as an asymmetry seed in these implosions. The simulations brought to bear on the problem (1D LILAC, 2D xRAGE, 3D ASTER and 3D Chimera) show how thermal Tion is expected to be significantly lower than Tion as inferred from the broadening of measured neutron spectra. They also show that the electron temperature is not expected to be the same as Tion for these implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Tripled yield in direct-drive laser fusion through statistical modelling

Accurate predictive models are essential to the design of high-performance, laser-fusion experiments. Here, we report the development of a promising statistical approach that has been used to quantitatively predict and design several cryogenic deuterium-tritium (DT) implosions on the OMEGA Laser System, leading to the tripling of the fusion yield to its highest value for direct-drive laser fusion of DT-layered targets. When scaled to National Ignition Facility laser energies of 1.9 MJ, these targets are predicted to produce a fusion energy output of ~500 kJ—several times larger than current fusion yields achieved at that facility. Future applications of this approach will guide the exploration of the vast parameter space for the conditions required for thermonuclear ignition and expose gaps in our understanding of laser-fusion physics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Inferring fuel areal density from secondary neutron yields in laser-driven magnetized liner inertial fusion

A technique to infer the areal density &rho;R of compressed deuterium (D) in cylindrical implosions from the ratio of secondary D–T (deuterium–tritium) neutrons to primary D–D neutrons is described and evaluated. For &rho;R to be proportional to the ratio of D–T to D–D yield, the increase in the D–T fusion cross section with collisional slowing of the tritium must be small, requiring where TkeV is the electron temperature in keV. The technique is applied to results from laser-driven magnetized liner inertial fusion (MagLIF) targets on OMEGA, where &rho;R is certainly less than 4 mg/cm 2 . OMEGA MagLIF targets do not achieve a sufficiently high, radially integrated, axial magnetic field BR to confine the tritium, as occurs in Z MagLIF targets, because they are ~10&times; smaller in radius. The inferred areal densities show that fuel convergence is reduced by preheating, by an applied axial magnetic field, and by increasing the initial fuel density, which are key features of the MagLIF scheme. The results are compared with 1-D and 2-D magnetohydrodynamic simulations for nominal laser and target parameters, which predict areal densities 2&times; to 3&times; higher than the measurements.

Davies, J. R.↗
DOE OSTI2019

Impact of imposed mode 2 laser drive asymmetry on inertial confinement fusion implosions

Low-mode asymmetries have emerged as one of the primary challenges to achieving high-performing inertial confinement fusion implosions. These asymmetries seed flows in the implosions, which will manifest as modifications to the measured ion temperature (T ion ) as inferred from the broadening of primary neutron spectra. The effects are important to understand (i) to learn to control and mitigate low-mode asymmetries and (ii) to experimentally more closely capture thermal T ion used as input in implosion performance metric calculations. Here, in this paper, results from and simulations of a set of experiments with a seeded mode 2 in the laser drive are described. The goal of this intentionally asymmetrically driven experiment was to test our capability to predict and measure the signatures of flows seeded by the low-mode asymmetry. The results from these experiments [first discussed in M. Gatu Johnson et al., Phys. Rev. E 98, 051201(R) (2018)] demonstrate the importance of interplay of flows seeded by various asymmetry seeds. In particular, measured T ion and self-emission x-ray asymmetries are expected to be well captured by interplay between flows seeded by the imposed mode 2 and the capsule stalk mount. Measurements of areal density asymmetry also indicate the importance of the stalk mount as an asymmetry seed in these implosions. The simulations brought to bear on the problem (1D LILAC, 2D xRAGE, 3D ASTER, and 3D Chimera) show how thermal T ion is expected to be significantly lower than T ion as inferred from the broadening of measured neutron spectra. They also show that the electron temperature is not expected to be the same as T ion for these implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

Measurements of yield, ion temperature, areal density (rhoR), shell convergence, and bang time have been obtained in shock-driven, D2 and D3He gas-filled “exploding-pusher” inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF) to assess the impact of ion kinetic effects. These measurements probed the shock convergence phase of ICF implosions, a critical stage in hot-spot ignition experiments. The data complement previous studies of kinetic effects in shock-driven implosions. Ion temperature and fuel rhoR inferred from fusion-product spectroscopy are used to estimate the ion-ion mean free path in the gas. A trend of decreasing yields relative to the predictions of 2D draco hydrodynamics simulations with increasing Knudsen number (the ratio of ion-ion mean free path to minimum shell radius) suggests that ion kinetic effects are increasingly impacting the hot fuel region, in general agreement with previous results. The long mean free path conditions giving rise to ion kinetic effects in the gas are often prevalent during the shock phase of both exploding pushers and ablatively-driven implosions, including ignition-relevant implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Impact of asymmetries on fuel performance in Inertial Confinement Fusion

Low-mode asymmetries prevent effective compression, confinement and heating of the fuel in inertial confinement fusion (ICF) implosions and their control is essential to achieving ignition. Ion temperatures (Tion) in ICF experiments are inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn also impacts broadening and will lead to artificially inflated “Tion” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured Tion. We report on intentionally asymmetrically driven experiments at the OMEGA laser facility designed to test the ability to accurately predict and measure line-of-sight differences in apparent Tion due to low-mode asymmetry-seeded flows. Contrasted to Chimera and xRAGE simulations, the measurements demonstrate how all asymmetry seeds have to be considered to fully capture the flow field in an implosion. In particular, flow induced by the stalk that holds the target is found to interfere with the seeded asymmetry. A substantial stalk-seeded asymmetry in the areal density of the implosion is also observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Impact of asymmetries on fuel performance in inertial confinement fusion

Low-mode asymmetries prevent effective compression, confinement, and heating of the fuel in inertial confinement fusion (ICF) implosions, and their control is essential to achieving ignition. Ion temperatures (T ion ) in ICF experiments are inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn also impacts broadening and will lead to artificially inflated “T ion ” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured T ion . Here we report on intentionally asymmetrically driven experiments at the OMEGA laser facility designed to test the ability to accurately predict and measure line-of-sight differences in apparent T ion due to low-mode asymmetry-seeded flows. Contrasted to chimera and xrage simulations, the measurements demonstrate how all asymmetry seeds have to be considered to fully capture the flow field in an implosion. In particular, flow induced by the stalk that holds the target is found to interfere with the seeded asymmetry. A substantial stalk-seeded asymmetry in the areal density of the implosion is also observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Using Inertial Fusion Implosions to Measure the T + 3 He Fusion Cross Section at Nucleosynthesis-Relevant Energies

Light nuclei were created during big-bang nucleosynthesis (BBN). Standard BBN theory, using rates inferred from accelerator-beam data, cannot explain high levels of Li6 in low-metallicity stars. Using high-energy-density plasmas we measure the T(He3,?)Li6 reaction rate, a candidate for anomalously high Li6 production; we find that the rate is too low to explain the observations, and different than values used in common BBN models. This is the first data directly relevant to BBN, and also the first use of laboratory plasmas, at comparable conditions to astrophysical systems, to address a problem in nuclear astrophysics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Indications of flow near maximum compression in layered DT implosions at the National Ignition Facility

An accurate understanding of burn dynamics in implosions of cryogenically layered deuterium and tritium (DT) filled capsules, obtained partly through precision diagnosis of these experiments, is essential for assessing the impediments to achieving ignition at the National Ignition Facility (NIF). We present measurements of neutrons from such implosions. The apparent ion temperatures (Tion) are inferred from the variance of the primary neutron spectrum. Consistently higher DT than DD Tions are observed, and the difference is seen to increase with increasing apparent DT Tion. The line-of-sight r.m.s. variations of both DD and DT Tion are small, ~150 eV, indicating an isotropic source. DD neutron yields are consistently high relative to the DT neutron yields given the observed Tions. Spatial and temporal variations of the DT temperature and density, DD-DT differential attenuation in the surrounding DT fuel, and fluid motion variations contribute to DT Tion > DD Tion, but are in a 1D model insufficient to explain the data. We hypothesize that in a 3D interpretation, these effects combined could explain the results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗