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© 2021 Author(s). A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps-20 ps). Maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.

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)

We have developed an experimental platform to generate radiatively heated solid density samples for warm dense matter studies at the OMEGA laser facility. Cylindrical samples of boron and beryllium are isochorically heated by K- and L-shell emission from x-ray converter foils wrapped around the cylinders' radii. X-ray Thomson scattering (XRTS) measures the temperature and the ionization state of the samples as function of time. Temperatures approach 10 eV, and the ionization states are found to be Z[subscript B]=3 and Z[subscript Be]=2. Radiation hydrodynamics simulations were performed to confirm a homogeneous plasma state exists in the center of the sample for the duration of the experiment. Results from the study can be extended to improve understanding of radiative heating processes in the warm dense matter regime., United States. National Nuclear Security Administration. Stewardship Science Graduate Fellowship Program (Grant DENA002135)

Fuel-ion species dynamics in hydrodynamiclike shock-driven DT³He-filled inertial confinement fusion implosion is quantitatively assessed for the first time using simultaneously measured D³He and DT reaction histories. These reaction histories are measured with the particle x-ray temporal diagnostic, which captures the relative timing between different nuclear burns with unprecedented precision (∼10 ps). The observed 50±10 ps earlier D³He reaction history timing (relative to DT) cannot be explained by average-ion hydrodynamic simulations and is attributed to fuel-ion species separation between the D, T, and ³He ions during shock convergence and rebound. At the onset of the shock burn, inferred ³He/T fuel ratio in the burn region using the measured reaction histories is much higher as compared to the initial gas-filled ratio. As T and ³He have the same mass but different charge, these results indicate that the charge-to-mass ratio plays an important role in driving fuel-ion species separation during strong shock propagation even for these hydrodynamiclike plasmas., United States. Department of Energy (Grant DE-FC52-08NA28752)

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[subscript 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[subscript ion]” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured T[subscript ion]. 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[subscript 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., United States. Department of Energy (Award DE-NA0002949)

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)

The significance and nature of ion kinetic effects in D[subscript 3]He-filled, shock-driven inertial confinement fusion implosions are assessed through measurements of fusion burn profiles. Over this series of experiments, the ratio of ion-ion mean free path to minimum shell radius (the Knudsen number, N[subscript K]) was varied from 0.3 to 9 in order to probe hydrodynamic-like to strongly kinetic plasma conditions; as the Knudsen number increased, hydrodynamic models increasingly failed to match measured yields, while an empirically-tuned, first-step model of ion kinetic effects better captured the observed yield trends [Rosenberg et al., Phys. Rev. Lett. 112, 185001 (2014)]. Here, spatially resolved measurements of the fusion burn are used to examine kinetic ion transport effects in greater detail, adding an additional dimension of understanding that goes beyond zero-dimensional integrated quantities to one-dimensional profiles. In agreement with the previous findings, a comparison of measured and simulated burn profiles shows that models including ion transport effects are able to better match the experimental results. In implosions characterized by large Knudsen numbers (N[subscript K] ∼ 3), the fusion burn profiles predicted by hydrodynamics simulations that exclude ion mean free path effects are peaked far from the origin, in stark disagreement with the experimentally observed profiles, which are centrally peaked. In contrast, a hydrodynamics simulation that includes a model of ion diffusion is able to qualitatively match the measured profile shapes. Therefore, ion diffusion or diffusion-like processes are identified as a plausible explanation of the observed trends, though further refinement of the models is needed for a more complete and quantitative understanding of ion kinetic effects., United States. Department of Energy (Grant DE-NA0001857), United States. Department of Energy (Grant DE-FC52-08NA28752)

An accurate understanding of burn dynamics in implosions of cryogenically layered deuterium (D) and tritium (T) filled capsules, obtained partly through precision diagnosis of these experiments, is essential for assessing the impediments to achieving ignition at the National Ignition Facility. We present measurements of neutrons from such implosions. The apparent ion temperatures T[subscript ion] are inferred from the variance of the primary neutron spectrum. Consistently higher DT than DD T[subscript ion] are observed and the difference is seen to increase with increasing apparent DT T[subscript ion]. The line-of-sight rms variations of both DD and DT T[subscript ion] are small, ∼ 150 eV, indicating an isotropic source. The DD neutron yields are consistently high relative to the DT neutron yields given the observed T[subscript ion]. 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 a DT T[subscript ion] greater than the DD T[subscript ion], but are in a one-dimensional model insufficient to explain the data. We hypothesize that in a three-dimensional interpretation, these effects combined could explain the results., Lawrence Livermore National Laboratory (Contract No. DE-AC52- 07NA27344)

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)10.1103/PhysRevLett.117.025001] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions., United States. Department of Energy (DE-FC02-04ER54789), United States. National Nuclear Security Administration (DE-NA0001944)

Three orthogonal proton emission imaging cameras were used to study the 3D effects of low-mode drive asymmetries and target asymmetries on nuclear burn symmetry and yield in direct-drive, inertial-confinement-fusion experiments. The fusion yield decreased quickly as the burn region became asymmetric due to either drive or capsule asymmetry. Measurements and analytic scaling are used to predict how intentionally asymmetric capsule shells could improve performance by compensating for drive asymmetry when it cannot be avoided (such as with indirect drive or with polar direct drive)., United States. Department of Energy (Grant DE-NA0002726), United States. Department of Energy (Grant DE-NA0002949)

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)

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a “high-foot” laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10[superscript 16] neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel., United States. Dept. of Energy (Lawrence Livermore National Laboratory Contract 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)

The ablator couples energy between the driver and fusion fuel in inertial confinement fusion (ICF). Because of its low opacity, high solid density, and material properties, beryllium has long been considered an ideal ablator for ICF ignition experiments at the National Ignition Facility. We report here the first indirect drive Be implosions driven with shaped laser pulses and diagnosed with fusion yield at the OMEGA laser. The results show good performance with an average DD neutron yield of ~2 × 10[superscript 9] at a convergence ratio of R[subscript 0]/R ~ 10 and little impact due to the growth of hydrodynamic instabilities and mix. In addition, the effect of adding an inner liner of W between the Be and DD is demonstrated., United States. Dept. of Energy (Lawrence Livermore National Laboratory Contract DE-AC52-07NA27344)

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)

We present the first results from an experimental campaign to measure the atomic ablator-gas mix in the deceleration phase of gas-filled capsule implosions on the National Ignition Facility. Plastic capsules containing CD layers were filled with tritium gas; as the reactants are initially separated, DT fusion yield provides a direct measure of the atomic mix of ablator into the hot spot gas. Capsules were imploded with x rays generated in hohlraums with peak radiation temperatures of ~294 eV. While the TT fusion reaction probes conditions in the central part (core) of the implosion hot spot, the DT reaction probes a mixed region on the outer part of the hot spot near the ablator–hot-spot interface. Experimental data were used to develop and validate the atomic-mix model used in two-dimensional simulations., United States. Dept. of Energy (Lawrence Livermore National Laboratory Contract DE-AC52-07NA27344)

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)

Neutron time-of-flight spectra from inertial confinement fusion experiments with tritium-filled targets have been measured at the National Ignition Facility. These spectra represent a significant improvement in energy resolution and statistics over previous measurements, and afford the first definitive observation of a peak resulting from sequential decay through the ground state of [superscript 5]He at low reaction energies E[subscript c.m.]≲100 keV. To describe the spectrum, we have developed an R-matrix model that accounts for interferences from fermion symmetry and intermediate states, and show these effects to be non-negligible. We also find the spectrum can be described by sequential decay through ℓ=1 states in [superscript 5]He, which differs from previous interpretations., Lawrence Livermore National Security (Contract DE-AC52-07NA27344)

Energy spectra and spectrally resolved one-dimensional fluence images of self-emitted charged-fusion products (14.7 MeV D[superscript 3]He protons) are routinely measured from indirectly driven inertial-confinement fusion (ICF) experiments utilizing ignition-scaled hohlraums at the National Ignition Facility (NIF). A striking and consistent feature of these images is that the fluence of protons leaving the ICF target in the direction of the hohlraum's laser entrance holes (LEHs) is very nonuniform spatially, in contrast to the very uniform fluence of protons leaving through the hohlraum equator. In addition, the measured nonuniformities are unpredictable, and vary greatly from shot to shot. These observations were made separately at the times of shock flash and of compression burn, indicating that the asymmetry persists even at ~0.5–2.5 ns after the laser has turned off. These phenomena have also been observed in experiments on the OMEGA laser facility with energy-scaled hohlraums, suggesting that the underlying physics is similar. Comprehensive data sets provide compelling evidence that the nonuniformities result from proton deflections due to strong spontaneous electromagnetic fields around the hohlraum LEHs. Although it has not yet been possible to uniquely determine whether the fields are magnetic (B) or electric (E), preliminary analysis indicates that the strength is ~1 MG if B fields or ~10[superscript 9] V cm[superscript −1] if E fields. These measurements provide important physics insight into the ongoing ignition experiments at the NIF. Understanding the generation, evolution, interaction and dissipation of the self-generated fields may help to answer many physics questions, such as why the electron temperatures measured in the LEH region are anomalously large, and may help to validate hydrodynamic models of plasma dynamics prior to plasma stagnation in the center of the hohlraum., United States. Dept. of Energy (DE-FG52-07 NA280 59), United States. Dept. of Energy (DE-FG03-03SF22691), Lawrence Livermore National Laboratory (B543881), Lawrence Livermore National Laboratory (LD RD-08-ER-062), University of Rochester. Fusion Science Center (412761-G), General Atomics (DE-AC52-06NA 27279), Stewardship Science Graduate Fellowship (DE-FC52-08NA28752)

The deuterium-tritium (D-T) γ-to-neutron branching ratio [[superscript 3]H(d,γ)[superscript 5]He/[superscript 3]H(d,n)[superscript 4]He] was determined under inertial confinement fusion (ICF) conditions, where the center-of-mass energy of 14–24 keV is lower than that in previous accelerator-based experiments. A D-T branching ratio value of (4.2 ± 2.0) × 10[superscript −5] was determined by averaging the results of two methods: (1) a direct measurement of ICF D-T γ-ray and neutron emissions using absolutely calibrated detectors, and (2) a separate cross-calibration against the D-[superscript 3]He γ-to-proton branching ratio [[superscript 3]He(d,γ)[superscript 5]Li/[superscript 3]He(d,p)[superscript 4]He]. Neutron-induced backgrounds were significantly reduced as compared to traditional beam-target accelerator-based experiments due to the short pulse nature of ICF implosions and the use of gas Cherenkov γ-ray detectors with fast temporal responses and inherent energy thresholds. These measurements of the D-T branching ratio in an ICF environment test several theoretical assumptions about the nature of A = 5 systems, including the dominance of the 3/2[superscript +] resonance at low energies, the presence of the broad first excited state of [superscript 5]He in the spectra, and the charge-symmetric nature of the capture processes in the mirror systems [superscript 5]He and [superscript 5]Li., National Laser User’s Facility (United States. Dept. of Energy.) (Grant number DE-FG03-03SF2269), University of Rochester. Fusion Science Center (United States. Dept. of Energy.) (Grant. Number DE-FC02-04ER54789)

Ignition implosions on the National Ignition Facility [ J. D. Lindl et al. Phys. Plasmas 11 339 (2004)] are underway with the goal of compressing deuterium-tritium fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision to keep the fuel entropy and adiabat low and ρR high. The first series of precision tuning experiments on the National Ignition Facility, which use optical diagnostics to directly measure the strength and timing of all four shocks inside a hohlraum-driven, cryogenic liquid-deuterium-filled capsule interior have now been performed. The results of these experiments are presented demonstrating a significant decrease in adiabat over previously untuned implosions. The impact of the improved shock timing is confirmed in related deuterium-tritium layered capsule implosions, which show the highest fuel compression (ρR~1.0 g/cm[superscript 2]) measured to date, exceeding the previous record [ V. Goncharov et al. Phys. Rev. Lett. 104 165001 (2010)] by more than a factor of 3. The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation., Lawrence Livermore National Laboratory (Contract No. DE-AC52-07NA27344)

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm[superscript -2], which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1–1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275–300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25–35 μm. Neutron images of the implosion were used to estimate a fuel density of 500–800 g cm[superscript -3]., Lawrence Livermore National Laboratory (Contract No. DE-AC52-07NA27344)

This Letter reports the first time-gated proton radiography of the spatial structure and temporal evolution of how the fill gas compresses the wall blowoff, inhibits plasma jet formation, and impedes plasma stagnation in the hohlraum interior. The potential roles of spontaneously generated electric and magnetic fields in the hohlraum dynamics and capsule implosion are discussed. It is shown that interpenetration of the two materials could result from the classical Rayleigh-Taylor instability occurring as the lighter, decelerating ionized fill gas pushes against the heavier, expanding gold wall blowoff. This experiment showed new observations of the effects of the fill gas on x-ray driven implosions, and an improved understanding of these results could impact the ongoing ignition experiments at the National Ignition Facility., National Laser User’s Facility (DE-FG52-07NA28059 and DE-FG03-03SF22691), Lawrence Livermore National Laboratory (B543881 and LDRD-08- ER-062), University of Rochester. Laboratory for Laser Energetics (414090-G), University of Rochester. Fusion Science Center (412761-G), General Atomics (DE-AC52-06NA 27279), 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)

Measurements of the D(d,p)T (dd) and T(t,2n)[superscript 4]He (tt) reaction yields have been compared with those of the D(t,n)[superscript 4]He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility., University of Rochester. Fusion Science Center (412761-G), University of Rochester. Laboratory for Laser Energetics (414090-G), Lawrence Livermore National Laboratory (B580243), United States. Dept. of Energy (DE-NA0000877), United States. Dept. of Energy (DE-FG52-09NA29553)

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

The 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 Authority, University of Rochester, U.S. Department of Energy (Grant No. DE-FG02-04ER54768 and Cooperative Agreement Nos. DE-FC02-ER54789 and DE-FC52- 08NA28302,)

The performance of triple-picket deuterium-tritium cryogenic target designs on the OMEGA Laser System [T.R. Boehly et al., Opt. Commun. 133, 495 (1997)] is reported. These designs facilitate control of shock heating in low-adiabat inertial confinement fusion targets. Areal densities up to 300 mg=cm[superscript 2] (the highest ever measured in cryogenic deuterium-tritium implosions) are inferred in the experiments with an implosion velocity ~3×10[superscript 7] cm=s driven at peak laser intensities of 8×10[superscript 14] W=cm[superscript 2]. Extension of these designs to ignition on the National Ignition Facility [J. A. Paisner et al., Laser FocusWorld 30, 75 (1994)] is presented., United States. Office of Inertial Confinement Fusion (Cooperative Agreement No. DE-FC52-08NA28302), University of Rochester, New York State Energy Research and Development Authority