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We report on the first accurate validation of low-Z ion-stopping formalisms in the regime ranging from low-velocity ion stopping—through the Bragg peak—to high-velocity ion stopping in well-characterized high-energy-density plasmas. These measurements were executed at electron temperatures and number densities in the range of 1.4–2.8 keV and 4×10^{23}–8×10^{23} cm^{−3}, respectively. For these conditions, it is experimentally demonstrated that the Brown-Preston-Singleton formalism provides a better description of the ion stopping than other formalisms around the Bragg peak, except for the ion stopping at v_{i}∼0.3v_{th}, where the Brown-Preston-Singleton formalism significantly underpredicts the observation. It is postulated that the inclusion of nuclear-elastic scattering, and possibly coupled modes of the plasma ions, in the modeling of the ion-ion interaction may explain the discrepancy of ∼20% at this velocity, which would have an impact on our understanding of the alpha energy deposition and heating of the fuel ions, and thus reduce the ignition threshold in an ignition experiment. ©2019, U.S. DOE (grant no. DE-NA0002949)

Magnetic fields are ubiquitous in the Universe. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of the luminous matter. The standard theoretical model for the origin of these strong magnetic fields is through the amplification of tiny seed fields via turbulent dynamo to the level consistent with current observations. However, experimental demonstration of the turbulent dynamo mechanism has remained elusive, since it requires plasma conditions that are extremely hard to re-create in terrestrial laboratories. Here we demonstrate, using laser-produced colliding plasma flows, that turbulence is indeed capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. These results support the notion that turbulent dynamo is a viable mechanism responsible for the observed present-day magnetization., Seventh Framework Programme (European Commission) (Grant 256973), Seventh Framework Programme (European Commission) (Grant 247039), United States. Department of Energy (Lawrence Livermore National Laboratory. Contract B591485), United States. Department of Energy (Grant DE-NA0003539)

Few-body nuclear physics often relies upon phenomenological models, with new efforts at the ab initio theory reported recently; both need high-quality benchmark data, particularly at low center-of-mass energies. We use high-energy-density plasmas to measure the proton spectra from [superscript 3]He+T and [superscript 3]He + [superscript 3]He fusion. The data disagree with R-matrix predictions constrained by neutron spectra from T+T fusion. We present a new analysis of the [superscript 3]He + [superscript 3]He proton spectrum; these benchmarked spectral shapes should be used for interpreting low-resolution data, such as solar fusion cross-section measurements., United States. Department of Energy (Grant DE-NA0001857), United States. Department of Energy (Grant DE-FC52-08NA28752), United States. Department of Energy (Grant DE-FG02-88ER40387), United States. Department of Energy (Grant DE-NA0001837), United States. Department of Energy (Grant DE-AC52-06NA25396)), Lawrence Livermore National Laboratory (B597367), University of Rochester. Laboratory for Laser Energetics (415935-G), University of Rochester. Fusion Science Center (524431), National Laser User’s Facility (DE-NA0002035)

A study of the transition from collisional to collisionless plasma flows has been carried out at the National Ignition Facility using high Mach number (M>4) counterstreaming plasmas. In these experiments, CD-CD and CD-CH planar foils separated by 6–10 mm are irradiated with laser energies of 250 kJ per foil, generating ∼1000 km/s plasma flows. Varying the foil separation distance scales the ion density and average bulk velocity and, therefore, the ion-ion Coulomb mean free path, at the interaction region at the midplane. The characteristics of the flow interaction have been inferred from the neutrons and protons generated by deuteron-deuteron interactions and by x-ray emission from the hot, interpenetrating, and interacting plasmas. A localized burst of neutrons and bright x-ray emission near the midpoint of the counterstreaming flows was observed, suggesting strong heating and the initial stages of shock formation. As the separation of the CD-CH foils increases we observe enhanced neutron production compared to particle-in-cell simulations that include Coulomb collisions, but do not include collective collisionless plasma instabilities. The observed plasma heating and enhanced neutron production is consistent with the initial stages of collisionless shock formation, mediated by the Weibel filamentation instability.

The remarkable discovery by the Chandra X-ray observatory that the Crab nebula’s jet periodically changes direction provides a challenge to our understanding of astrophysical jet dynamics. It has been suggested that this phenomenon may be the consequence of magnetic fields and magnetohydrodynamic instabilities, but experimental demonstration in a controlled laboratory environment has remained elusive. Here we report experiments that use high-power lasers to create a plasma jet that can be directly compared with the Crab jet through well-defined physical scaling laws. The jet generates its own embedded toroidal magnetic fields; as it moves, plasma instabilities result in multiple deflections of the propagation direction, mimicking the kink behaviour of the Crab jet. The experiment is modelled with three-dimensional numerical simulations that show exactly how the instability develops and results in changes of direction of the jet., United States. Department of Energy (Grant DE-FG03-09NA29553), United States. Department of Energy (Grant DE-SC0007168), University of Rochester. Laboratory for Laser Energetics (414090-G), National Laser User’s Facility (DE-NA0000877), University of Rochester. Fusion Science Center (415023-G), Lawrence Livermore National Laboratory (B580243)

A new technique that uses inertial confinement implosions for measuring low-energy nuclear reactions important to nuclear astrophysics is described. Simultaneous measurements of n–D and n–T elastic scattering at 14.1 MeV using deuterium–tritium gas-filled capsules provide a proof of principle for this technique. Measurements have been made of D(d,p)T (dd) and T(t,2n)[superscript 4]He (tt) reaction yields relative to the D(t,n)[superscript]He (dt) reaction yield for deuterium–tritium mixtures with fT/fD between 0.62 and 0.75 and for a wide range of ion temperatures to test our understanding of the implosion processes. Measurements of the shape of the neutron spectrum from the T(t,2n)[superscript 4]He reaction have been made for each of these target configurations., National Laser User’s Facility (Grant NA0000877), United States. Dept. of Energy (Grant DE-FG52-09NA29553), University of Rochester. Fusion Science Center (Rochester Subaward 415023-G, UR Account 5-24431), University of Rochester. Laboratory for Laser Energetics (Grant 412160-001G), Lawrence Livermore National Laboratory (Grants B580243 and DE-AC52-07NA27344)

Anomalous reduction of the fusion yields by 50% and anomalous scaling of the burn-averaged ion temperatures with the ion-species fraction has been observed for the first time in D[superscript 3]He-filled shock-driven inertial confinement fusion implosions. Two ion kinetic mechanisms are used to explain the anomalous observations: thermal decoupling of the D and [superscript 3]He populations and diffusive species separation. The observed insensitivity of ion temperature to a varying deuterium fraction is shown to be a signature of ion thermal decoupling in shock-heated plasmas. The burn-averaged deuterium fraction calculated from the experimental data demonstrates a reduction in the average core deuterium density, as predicted by simulations that use a diffusion model. Accounting for each of these effects in simulations reproduces the observed yield trends., United States. National Nuclear Security Administration (Grant DE-NA0001857), University of Rochester. Fusion Science Center (Grant 415023-G), National Laser User’s Facility (Grant DE-NA0002035), University of Rochester. Laboratory for Laser Energetics (Grant 415935-G), Lawrence Livermore National Laboratory (Grant B600100)

We measured the stopping of energetic protons in an isochorically heated solid-density Be plasma with an electron temperature of ~32 eV, corresponding to moderately coupled [(e[superscript 2]/a)/(k[subscript B]T[subscript e] + E[subscript F]) ~ 0.3] and moderately degenerate [k[subscript B]T[subscript e]/E[subscript F] ~ 2] “warm-dense matter” (WDM) conditions. We present the first high-accuracy measurements of charged-particle energy loss through dense plasma, which shows an increased loss relative to cold matter, consistent with a reduced mean ionization potential. The data agree with stopping models based on an ad hoc treatment of free and bound electrons, as well as the average-atom local-density approximation; this work is the first test of these theories in WDM plasma., United States. Dept. of Energy (Grant DE-NA0001857), United States. Dept. of Energy (Grant DE-FC52-08NA28752), Lawrence Livermore National Laboratory (Grant B597367), University of Rochester. Laboratory for Laser Energetics (Grant 415935-G), University of Rochester. Fusion Science Center (Grant 524431), National Laser User’s Facility (Grant DE-NA0002035), National Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374)

Monoenergetic-proton radiographs of laser-generated, high-Mach-number plasma jets colliding at various angles shed light on the structures and dynamics of these collisions. The observations compare favorably with results from 2D hydrodynamic simulations of multistream plasma jets, and also with results from an analytic treatment of electron flow and magnetic field advection. In collisions of two noncollinear jets, the observed flow structure is similar to the analytic model’s prediction of a characteristic feature with a narrow structure pointing in one direction and a much thicker one pointing in the opposite direction. Spontaneous magnetic fields, largely azimuthal around the colliding jets and generated by the well-known ∇T[subscript e] × ∇n[subscript e] Biermann battery effect near the periphery of the laser spots, are demonstrated to be “frozen in” the plasma (due to high magnetic Reynolds number Re[subscript M] ~ 5 × 10[superscript 4]) and advected along the jet streamlines of the electron flow. These studies provide novel insight into the interactions and dynamics of colliding plasma jets., United States. Dept. of Energy (University of Rochester. Laboratory for Laser Energetics. National Laser User’s Facility DE-FG52-07NA28 059), United States. Dept. of Energy (University of Rochester. Laboratory for Laser Energetics. National Laser User’s Facility DE-FG03-03SF22691), Lawrence Livermore National Laboratory (B543881), Lawrence Livermore National Laboratory (LDRD-08-ER-062), University of Rochester. Laboratory for Laser Energetics (414090-G), University of Rochester. Fusion Science Center (412761-G)

Clear evidence of the transition from hydrodynamiclike to strongly kinetic shock-driven implosions is, for the first time, revealed and quantitatively assessed. Implosions with a range of initial equimolar D[superscript 3]He gas densities show that as the density is decreased, hydrodynamic simulations strongly diverge from and increasingly overpredict the observed nuclear yields, from a factor of ∼2 at 3.1 mg/cm[superscript 3] to a factor of 100 at 0.14 mg/cm[superscript 3]. (The corresponding Knudsen number, the ratio of ion mean-free path to minimum shell radius, varied from 0.3 to 9; similarly, the ratio of fusion burn duration to ion diffusion time, another figure of merit of kinetic effects, varied from 0.3 to 14.) This result is shown to be unrelated to the effects of hydrodynamic mix. As a first step to garner insight into this transition, a reduced ion kinetic (RIK) model that includes gradient-diffusion and loss-term approximations to several transport processes was implemented within the framework of a one-dimensional radiation-transport code. After empirical calibration, the RIK simulations reproduce the observed yield trends, largely as a result of ion diffusion and the depletion of the reacting tail ions., United States. Dept. of Energy (Grant DE-NA0001857), United States. Dept. of Energy (Grant DE-FC52-08NA28752), University of Rochester. Fusion Science Center (5-24431), National Laser User’s Facility (DE-NA0002035), University of Rochester. Laboratory for Laser Energetics (415935-G), Lawrence Livermore National Laboratory (B597367)

A strong nonhydrodynamic mechanism generating atomic fuel-shell mix has been observed in strongly shocked inertial confinement fusion implosions of thin deuterated-plastic shells filled with [superscript 3]He gas. These implosions were found to produce D[superscript 3]He-proton shock yields comparable to implosions of identical shells filled with a hydroequivalent 50∶50 D[superscript 3]He gas mixture. Standard hydrodynamic mixing cannot explain this observation, as hydrodynamic modeling including mix predicts a yield an order of magnitude lower than was observed. Instead, these results can be attributed to ion diffusive mix at the fuel-shell interface., United States. Dept. of Energy (Grant DE-NA0001857), University of Rochester. Fusion Science Center (Grant 5-24431), National Laser User’s Facility (Grant DE-NA0002035), University of Rochester. Laboratory for Laser Energetics (Grant 415935-G), Lawrence Livermore National Laboratory (Grant B597367), United States. National Nuclear Security Administration (Stewardship Science Graduate Fellowship DE-FC52-08NA28752)

For the first time the differential cross section for the elastic neutron-triton (n-[superscript 3]H) and neutron-deuteron (n-[superscript 2]H) scattering at 14.1 MeV has been measured by using an inertial confinement fusion facility. In these experiments, which were carried out by simultaneously measuring elastically scattered [superscript 3]H and [superscript 2]H ions from a deuterium-tritium gas-filled inertial confinement fusion capsule implosion, the differential cross section for the elastic n-[superscript 3]H scattering was obtained with significantly higher accuracy than achieved in previous accelerator experiments. The results compare well with calculations that combine the resonating-group method with an ab initio no-core shell model, which demonstrate that recent advances in ab initio theory can provide an accurate description of light-ion reactions., United States. Dept. of Energy (Grant No. NA0000877), University of Rochester. Fusion Science Center (Rochester Subaward PO No. 415023-G, UR Account No. 5-24431), United States. Dept. of Energy (Grant No. DE-FG03-03SF22691), University of Rochester. Laboratory for Laser Energetics (Grant No. 412160-001G), Lawrence Livermore National Laboratory (Grant No. B504974), United States. Dept. of Energy (Grant No. DE-AC52-06NA27279)

Measurements of the neutron spectrum from the T(t,2n)[superscript 4]He (tt) reaction have been conducted using inertial confinement fusion implosions at the OMEGA laser facility. In these experiments, deuterium-tritium (DT) gas-filled capsules were imploded to study the tt reaction in thermonuclear plasmas at low reactant center-of-mass (c.m.) energies. In contrast to accelerator experiments at higher c.m. energies (above 100 keV), these results indicate a negligible n+[superscript 5]He reaction channel at a c.m. energy of 23 keV., United States. Dept. of Energy (grant no. DE-FG52-09NA29553), National Laser User’s Facility (grant no. NA0000877), University of Rochester. Fusion Science Center (subaward PO no. 415023-G, UR acct. no. 5-24431), University of Rochester. Laboratory for Laser Energetics (grant no. 412160-001G), Lawrence Livermore National Laboratory (grant nos. B580243 and DE-AC52-07NA27344)

An analytic model is developed for energetic electrons interacting with plasmas. This model rigorously treats the effects of energy loss upon Coulomb interactions and reveals several important features, including the coupling of scattering and energy loss—which previous calculations had erroneously treated as independent in cases where an electron lost a significant amount (or all) of its energy. The unique transparency and generality of these calculations allows for straightforward applications when quantitatively evaluating the energy deposition of energetic electrons in various plasmas, including those in inertial confinement fusion., LLE (Grant No. 414090-G), Fusion Science Center at University of Rochester (Grant No. 412761-G), U.S. Department of Energy Contract (Grants No. DE-FG52-07NA28059 and No. DE-FG52-06N826203)

Unique detection of electromagnetic fields and identification of field type and strength as a function of position were used to determine the nature of self-generated fields in a novel experiment with laser-generated plasma bubbles on two sides of a plastic foil. Field-induced deflections of monoenergetic 15-MeV probe protons passing through the two bubbles, measured quantitatively with proton radiography, were combined with Lorentz mapping to provide separate measurements of magnetic and electric fields. The result was absolute identification and measurement of a toroidal magnetic field around each bubble and determination that any electric field component parallel to the foil was below measurement uncertainties., Lawrence Livermore National Laboratory, Office of Defense Programs, National Laser Users Facility, Department of Energy, University of Rochester Fusion Science Center

Direct-drive implosions with 20-μm-thick glass shells were conducted on the Omega Laser Facility to test the performance of high-Z glass ablators for direct-drive, inertial confinement fusion. The x-ray signal caused by hot electrons generated by two-plasmon-decay instability was reduced by more than ~40× and hot-electron temperature by ~2× in the glass compared to plastic ablators at ignition-relevant drive intensities of ~1×10[superscript 15] W/cm[superscript 2], suggesting reduced target preheat. The measured absorption and compression were close to 1D predictions. The measured soft x-ray production in the spectral range of ~2 to 4 keV was ~2× to 3× lower than 1D predictions, indicating that the shell preheat caused by soft x-rays is less than predicted. A direct-drive-ignition design based on glass ablators is introduced., United States. Dept. of Energy. Office of Inertial Confinement Fusion (Cooperative Agreement No. DE-FC52-08NA28302), University of Rochester, New York State Energy Research and Development Authority

The 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 Authority, University of Rochester, U.S. Department of Energy, Office of Inertial Confinement Fusion (Cooperative Agreement No. DE-FC52-08NA28302)

Recent 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 Center, Laboratory for Laser Energetics, Lawrence Livermore National Laboratory, Department of Energy