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A compact neutron spectrometer, based on a CH foil for the production of recoil protons and CR-39 detection, is being developed for the measurements of the DD-neutron spectrum at the NIF, OMEGA, and Z facilities. As a CR-39 detector will be used in the spectrometer, the principal sources of background are neutron-induced tracks and intrinsic tracks (defects in the CR-39). To reject the background to the required level for measurements of the down-scattered and primary DD-neutron components in the spectrum, the Coincidence Counting Technique (CCT) must be applied to the data. Using a piece of CR-39 exposed to 2.5-MeV protons at the MIT HEDP accelerator facility and DD-neutrons at Z, a significant improvement of a DD-neutron signal-to-background level has been demonstrated for the first time using the CCT. These results are in excellent agreement with previous work applied to DT neutrons. [ABSTRACT FROM AUTHOR]

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 4×1023-8×1023 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 vi~0.3vth, 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ³He+T and ³He+³He fusion. The data disagree with R-matrix predictions constrained by neutron spectra from T+T fusion. We present a new analysis of the ³He+³He proton spectrum; these benchmarked spectral shapes should be used for interpreting low-resolution data, such as solar fusion cross-section measurements. [ABSTRACT FROM AUTHOR]

Light nuclei were created during big-bang nucleosynthesis (BBN). Standard BBN theory, using rates inferred from accelerator-beam data, cannot explain high levels of 6Li in low-metallicity stars. Using high-energy-density plasmas we measure the T(³He,γ)6Li reaction rate, a candidate for anomalously high 6Li 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. [ABSTRACT FROM AUTHOR]

The neutron spectrum produced by deuterium-tritium (DT) inertial confinement fusion implosions contains a wealth of information about implosion performance including the DT yield, ion-temperature, and areal-density. The Magnetic Recoil Spectrometer (MRS) has been used at both the OMEGA laser facility and the National Ignition Facility (NIF) to measure the absolute neutron spectrum from 3 to 30 MeV at OMEGA and 3 to 36 MeV at the NIF. These measurements have been used to diagnose the performance of cryogenic target implosions to unprecedented accuracy. Interpretation of MRS data requires a detailed understanding of the MRS response and background. This paper describes ab initio characterization of the system involving Monte Carlo simulations of the MRS response in addition to the commission experiments for in situ calibration of the systems on OMEGA and the NIF. [ABSTRACT FROM AUTHOR]

For the first time, quantitative measurements of collective fuel velocities in Inertial Confinement Fusion implosions at the National Ignition Facility are reported. Velocities along the line-of-sight (LOS) of the Magnetic Recoil neutron Spectrometer (MRS), positioned close to the equator (73°-324°), were inferred from the measured mean energy of the deuterium-tritium (DT)-primary neutron peak. Substantial mean energy shifts up to 113 ± 16 keV were observed in DT gas-filled exploding-pusher implosions, driven in a polar-direct drive configuration, which corresponds to bulk fuel velocities up to 210 ± 30 km/s. In contrast, only marginal bulk fuel velocities along the MRS LOS were observed in cryogenically layered DT implosions. Integrated analysis of data from a large number of cryogenically layered implosions has recently identified a deficit in achieved hot-spot energy of ∼3 kJ for these implosions [C. Cerjan et al., Phys. Plasmas (2013)]. One hypothesis that could explain this missing energy is a collective, directional fuel velocity of ∼190 km/s. As only marginal bulk fuel velocities are observed in the MRS data, this might indicate that turbulent or radial flows would be a likely explanation for the missing energy. However, a directional velocity close to perpendicular to the MRS LOS cannot be ruled out. [ABSTRACT FROM AUTHOR]

A magnetic recoil spectrometer (MRS) has been installed and extensively used on OMEGA and the National Ignition Facility (NIF) for measurements of the absolute neutron spectrum from inertial confinement fusion implosions. From the neutron spectrum measured with the MRS, many critical implosion parameters are determined including the primary DT neutron yield, the ion temperature, and the down-scattered neutron yield. As the MRS detection efficiency is determined from first principles, the absolute DT neutron yield is obtained without cross-calibration to other techniques. The MRS primary DT neutron measurements at OMEGA and the NIF are shown to be in excellent agreement with previously established yield diagnostics on OMEGA, and with the newly commissioned nuclear activation diagnostics on the NIF. [ABSTRACT FROM AUTHOR]

DT neutron yield (Yn), ion temperature (Ti), and down-scatter ratio (dsr) determined from measured neutron spectra are essential metrics for diagnosing the performance of inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF). A suite of neutron-time-of-flight (nTOF) spectrometers and a magnetic recoil spectrometer (MRS) have been implemented in different locations around the NIF target chamber, providing good implosion coverage and the complementarity required for reliable measurements of Yn, Ti, and dsr. From the measured dsr value, an areal density (ρR) is determined through the relationship ρRtot (g/cm2) = (20.4 ± 0.6) × dsr10-12 MeV. The proportionality constant is determined considering implosion geometry, neutron attenuation, and energy range used for the dsr measurement. To ensure high accuracy in the measurements, a series of commissioning experiments using exploding pushers have been used for in situ calibration of the as-built spectrometers, which are now performing to the required accuracy. Recent data obtained with the MRS and nTOFs indicate that the implosion performance of cryogenically layered DT implosions, characterized by the experimental ignition threshold factor (ITFx), which is a function of dsr (or fuel ρR) and Yn, has improved almost two orders of magnitude since the first shot in September, 2010. [ABSTRACT FROM AUTHOR]

Measurements of the total energy carried by fast ablator-ions in direct-drive implosions on OMEGA have been conducted using magnetic and Thomson Parabola spectrometers. It is shown that the total laser energy lost to fast ablator-ions for plastic and glass targets is comparable and that it is a modest fraction of the incident laser energy (<=1%). These measurements have been used to infer a non-linear, voltage-dependent target capacitance (∼0.1 nF) associated with the space-charge that accelerates the fast-ions. [ABSTRACT FROM AUTHOR]

The MIT Linear Electrostatic Ion Accelerator (LEIA) generates DD and D3He fusion products for the development of nuclear diagnostics for Omega, Z, and the National Ignition Facility (NIF). Significant improvements to the system in recent years are presented. Fusion reaction rates, as high as 107 s-1 and 106 s-1 for DD and D3He, respectively, are now well regulated with a new ion source and electronic gas control system. Charged fusion products are more accurately characterized, which allows for better calibration of existing nuclear diagnostics. In addition, in situ measurements of the on-target beam profile, made with a CCD camera, are used to determine the metrology of the fusion-product source for particle-counting applications. Finally, neutron diagnostics development has been facilitated by detailed Monte Carlo N-Particle Transport (MCNP) modeling of neutrons in the accelerator target chamber, which is used to correct for scattering within the system. These recent improvements have resulted in a versatile platform, which continues to support the existing nuclear diagnostics while simultaneously facilitating the development of new diagnostics in aid of the National Ignition Campaign at the National Ignition Facility. [ABSTRACT FROM AUTHOR]

CR-39 proton radiography is an experimental charged-particle backlighter platform fielded and used at OMEGA and the NIF to image electric and magnetic fields in a subject plasma. Processing a piece of CR-39 involves etching it in hot NaOH, and the etch time can greatly impact the background-to-signal ratio (BSR) in low-fluence (≲4 × 104 cm-2) regions and detection efficiency in high-fluence regions (≳7 × 105 cm-2). For CR-39 data with high fluence variation, these effects mean that any single etch time will result in ≳15% error in the measured signal in either the high- or low-fluence regions. This study aims to quantify the impact of the etch time on the BSR and efficiency losses and how these affect the field reconstruction. Experiments at the MIT Linear Electrostatic Ion Accelerator provided empirical values of the BSR and efficiency losses as a function of the fluence and etch time for fluences ranging from 3 × 103 to 7 × 105 cm-2. Synthetic radiographs were generated with known fields and modulated based on empirical values of BSR and efficiency losses. The fields were reconstructed using a Monge-Ampère code with the modulated radiographs as input. The results indicate that combining short and long etches allows for more accurate analysis of radiographs with high fluence variation, with the mean squared error of the reconstructed fields decreasing by factors of 1.2-7 compared to the reconstructions using only one etch time., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).)

Shock-driven implosions with 100% deuterium (D&#95;{2}) gas fill compared to implosions with 50:50 nitrogen-deuterium (N&#95;{2}D&#95;{2}) gas fill have been performed at the OMEGA laser facility to test the impact of the added mid-Z fill gas on implosion performance. Ion temperature (T&#95;{ion}) as inferred from the width of measured DD-neutron spectra is seen to be 34%±6% higher for the N&#95;{2}D&#95;{2} implosions than for the D&#95;{2}-only case, while the DD-neutron yield from the D&#95;{2}-only implosion is 7.2±0.5 times higher than from the N&#95;{2}D&#95;{2} gas fill. The T&#95;{ion} enhancement for N&#95;{2}D&#95;{2} is observed in spite of the higher Z, which might be expected to lead to higher radiative loss, and higher shock strength for the D&#95;{2}-only versus N&#95;{2}D&#95;{2} implosions due to lower mass, and is understood in terms of increased shock heating of N compared to D, heat transfer from N to D prior to burn, and limited amount of ion-electron-equilibration-mediated additional radiative loss due to the added higher-Z material. This picture is supported by interspecies equilibration timescales for these implosions, constrained by experimental observables. The one-dimensional (1D) kinetic Vlasov-Fokker-Planck code ifp and the radiation hydrodynamic simulation codes hyades (1D) and xrage [1D, two-dimensional (2D)] are brought to bear to understand the observed yield ratio. Comparing measurements and simulations, the yield loss in the N&#95;{2}D&#95;{2} implosions relative to the pure D&#95;{2}-fill implosion is determined to result from the reduced amount of D&#95;{2} in the fill (fourfold effect on yield) combined with a lower fraction of the D&#95;{2} fuel being hot enough to burn in the N&#95;{2}D&#95;{2} case. The experimental yield and T&#95;{ion} ratio observations are relatively well matched by the kinetic simulations, which suggest interspecies diffusion is responsible for the lower fraction of hot D&#95;{2} in the N&#95;{2}D&#95;{2} relative to the D&#95;{2}-only case. The simulated absolute yields are higher than measured; a comparison of 1D versus 2D xrage simulations suggest that this can be explained by dimensional effects. The hydrodynamic simulations suggest that radiative losses primarily impact the implosion edges, with ion-electron equilibration times being too long in the implosion cores. The observations of increased T&#95;{ion} and limited additional yield loss (on top of the fourfold expected from the difference in D content) for the N&#95;{2}D&#95;{2} versus D&#95;{2}-only fill suggest it is feasible to develop the platform for studying CNO-cycle-relevant nuclear reactions in a plasma environment.

We report on measurements of the ion-electron energy-transfer cross section utilizing low-velocity ion stopping in high-energy-density plasmas at the OMEGA laser facility. These measurements utilize a technique that leverages the close relationship between low-velocity ion stopping and ion-electron equilibration. Shock-driven implosions of capsules filled with D^{3}He gas doped with a trace amount of argon are used to generate densities and temperatures in ranges from 1×10^{23} to 2×10^{24} cm^{-3} and from 1.4 to 2.5 keV, respectively. The energy loss of 1-MeV DD tritons and 3.7-MeV D^{3}He alphas that have velocities lower than the average velocity of the thermal electrons is measured. The energy loss of these ions is used to determine the ion-electron energy-transfer cross section, which is found to be in excellent agreement with quantum-mechanical calculations in the first Born approximation. This result provides an experimental constraint on ion-electron energy transfer in high-energy-density plasmas, which impacts the modeling of alpha heating in inertial confinement fusion implosions, magnetic-field advection in stellar atmospheres, and energy balance in supernova shocks.

Charged particle spectrometry is a critical diagnostic to study inertial-confinement-fusion plasmas and high energy density plasmas. The OMEGA Laser Facility has two fixed magnetic charged particle spectrometers (CPSs) to measure MeV-ions. In situ calibration of these spectrometers was carried out using 241 Am and 226 Ra alpha emitters. The alpha emission spectrum from the sources was measured independently using surface-barrier detectors (SBDs). The energy dispersion and broadening of the CPS systems were determined by comparing the CPS measured alpha spectrum to that of the SBD. The calibration method significantly constrains the energy dispersion, which was previously obtained through the measurement of charged particle fusion products. Overall, a small shift of 100 keV was observed between previous and the calibration done in this work.

Background: Good quality friendships and relationships are critical to the development of social competence and are associated with quality of life and mental health in childhood and adolescence. Through social distancing and isolation restrictions, the COVID-19 pandemic has had an impact on the way in which youth socialize and communicate with friends, peers, teachers and family on a daily basis. In order to understand children's social functioning during the pandemic, it is essential to gather information on their experiences and perceptions concerning the social changes unique to this period. The objective of this study was to document children and adolescents' perspectives regarding their social life and friendships during the COVID-19 pandemic, through qualitative interviews., Methods: Participants (N = 67, 5-14 years) were recruited in May and June 2020. Semi-structured interviews were conducted via a videoconferencing platform. A thematic qualitative analysis was conducted based on the transcribed and coded interviews (NVivo)., Results: The upheavals related to the pandemic provoked reflection among the participants according to three main themes, each of which included sub-themes: (1) the irreplaceable nature of friendship, (2) the unsuspected benefits of school for socialization and (3) the limits and possibilities of virtual socialization., Conclusions: The collection of rich, qualitative information on the perspectives of children and adolescents provides a deeper understanding of the consequences of the pandemic on their socialization and psychological health and contributes to our fundamental understanding of social competence in childhood., (© 2022 John Wiley & Sons Ltd.)

A system of x-ray imaging spectrometer (XRIS) has been implemented at the OMEGA Laser Facility and is capable of spatially and spectrally resolving x-ray self-emission from 5 to 40 keV. The system consists of three independent imagers with nearly orthogonal lines of sight for 3D reconstructions of the x-ray emission region. The distinct advantage of the XRIS system is its large dynamic range, which is enabled by the use of tantalum apertures with radii ranging from 50 μm to 1 mm, magnifications of 4 to 35×, and image plates with any filtration level. In addition, XRIS is capable of recording 1-100's images along a single line of sight, facilitating advanced statistical inference on the detailed structure of the x-ray emitting regions. Properties such as P0 and P2 of an implosion are measured to 1% and 10% precision, respectively. Furthermore, T e can be determined with 5% accuracy.

A knock-on deuteron imager (KoDI) has been implemented to measure the fuel and hotspot asymmetry of cryogenic inertial confinement fusion implosions on OMEGA. Energetic neutrons produced by D-T fusion elastically scatter ("knock on") deuterons from the fuel layer with a probability that depends on ρR. Deuterons above 10 MeV are produced by near-forward scattering, and imaging them is equivalent to time-integrated neutron imaging of the hotspot. Deuterons below 6 MeV are produced by a combination of side scattering and ranging in the fuel, and encode information about the spatial distribution of the dense fuel. The KoDI instrument consists of a multi-penumbral aperture positioned 10-20 cm from the implosion using a ten-inch manipulator and a detector pack at 350 cm from the implosion to record penumbral images with magnification of up to 35×. Range filters and the intrinsic properties of CR-39 are used to distinguish different charged-particle images by energy along the same line of sight. Image plates fielded behind the CR-39 record a 10 keV x-ray image using the same aperture. A maximum-likelihood reconstruction algorithm has been implemented to infer the source from the projected penumbral images. The effects of scattering and aperture charging on the instrument point-spread function are assessed. Synthetic data are used to validate the reconstruction algorithm and assess an appropriate termination criterion. Significant aperture charging has been observed in the initial experimental dataset, and increases with aperture distance from the implosion, consistent with a simple model of charging by laser-driven EMP.

Recent progress at the National Ignition Facility (NIF), with neutron yields of order 1 × 10 17 , places new constraints on diagnostics used to characterize implosion performance. The Magnetic Recoil neutron Spectrometer (MRS), which is routinely used to measure yield, ion temperature (T ion ), and down-scatter ratio (dsr), has been adapted to allow measurements of dsr up to 5 × 10 17 , and yield and T ion up to 2 × 10 18 in the near term with new data processing techniques and conversion foil solutions. This paper presents a solution for extending MRS operation up to a yield of 2 × 10 19 (60 MJ) by moving the spectrometer outside of the NIF shield wall. This will not only enhance the upper yield limit by 10× but also improve signal-to-background by 5×.

A series of thin glass-shell shock-driven DT gas-filled capsule implosions was conducted at the OMEGA laser facility. These experiments generate conditions relevant to the central plasma during the shock-convergence phase of ablatively driven inertial confinement fusion (ICF) implosions. The spectral temperatures inferred from the DTn and DDn spectra are most consistent with a two-ion-temperature plasma, where the initial apparent temperature ratio, T&#95;{T}/T&#95;{D}, is 1.5. This is an experimental confirmation of the long-standing conjecture that plasma shocks couple energy directly proportional to the species mass in multi-ion plasmas. The apparent temperature ratio trend with equilibration time matches expected thermal equilibration described by hydrodynamic theory. This indicates that deuterium and tritium ions have different energy distributions for the time period surrounding shock convergence in ignition-relevant ICF implosions.

A new tri-particle mono-energetic backlighter based on laser-driven implosions of DT 3 He gas-filled capsules has been implemented at the OMEGA laser. This platform, an extension of the original D 3 He backlighter platform, generates 9.5 MeV deuterons from the T 3 He reaction in addition to 14.7 and 3.0 MeV protons from the deuterium and helium-3 reactants. The monoenergetic 14.7 and 3.0 MeV protons have been used with success at OMEGA and the NIF for both radiography and stopping-power studies. There are several advantages of having a third particle to diagnose plasma conditions: an extra time-of-flight-separated radiograph and an improved ability to discern between electric and magnetic fields. In cases where the 3.0 MeV protons cannot penetrate an experiment, the benefit of the additional 9.5 MeV deuterons is magnified. This capability is well-suited for NIF experiments, where large fields and plasma densities often preclude useful 3.0 MeV proton data. The advantages are demonstrated with radiographs of OMEGA plasmas with magnetic and electric fields. Tests using backlighter-scale 420 μm diameter thin glass capsules validate the platform's extended backlighting capability. The performance characteristics of this backlighter, such as source size and timing, are discussed.

The Magnetic Recoil neutron Spectrometer (MRS) at the OMEGA laser facility has been routinely used to measure deuterium-tritium (DT) yield and areal density in cryogenically layered implosions since 2008. Recently, operation of the OMEGA MRS in higher-resolution mode with a new smaller, thinner (4 cm 2 , 57 μ m thick) CD 2 conversion foil has also enabled inference of the apparent DT ion temperature ( T ion ) from MRS data. MRS-inferred T ion compares well with T ion as measured using neutron time-of-flight spectrometers, which is important as it demonstrates good understanding of the very different systematics associated with the two independent measurements. The MRS resolution in this configuration, Δ E MRS = 0.91 MeV FWHM, is still higher than that required for a high-precision T ion measurement. We show how fielding a smaller foil closer to the target chamber center and redesigning the MRS detector array could bring the resolution to Δ E MRS = 0.45 MeV, reducing the systematic T ion uncertainty by more than a factor of 4.

Children with medical complexity (CMC) in rural and northern communities have more difficulty accessing subspecialty health providers than those in urban centres. This article describes an alignment cascade in which leaders engaged peers and staff to rapidly roll out the implementation of a sustainably designed complex care model, integrated in the Champlain Complex Care Program and delivered in Timmins, Ontario. The Provincial Council for Maternal and Child Health's Complex Care for Kids Ontario (CCKO) strategy supports the implementation and expansion of a hub-and-spoke model of interprofessional complex care for CMC and their families. A nurse practitioner is the primary point of contact for the family and oversees coordination and integration of care; regional CCKO programs are committed to building capacity to provide safe, high-quality care for CMC in communities closer to their homes., (Copyright © 2018 Longwoods Publishing.)

Magnetic reconnection, the annihilation and rearrangement of magnetic fields in a plasma, is a universal phenomenon that frequently occurs when plasmas carrying oppositely directed field lines collide. In most natural circumstances, the collision is asymmetric (the two plasmas having different properties), but laboratory research to date has been limited to symmetric configurations. In addition, the regime of strongly driven magnetic reconnection, where the ram pressure of the plasma dominates the magnetic pressure, as in several astrophysical environments, has also received little experimental attention. Thus, we have designed the experiments to probe reconnection in asymmetric, strongly driven, laser-generated plasmas. Here we show that, in this strongly driven system, the rate of magnetic flux annihilation is dictated by the relative flow velocities of the opposing plasmas and is insensitive to initial asymmetries. In addition, out-of-plane magnetic fields that arise from asymmetries in the three-dimensional plasma geometry have minimal impact on the reconnection rate, due to the strong flows.

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 D3He 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/cm3 to a factor of 100 at 0.14  mg/cm3. (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.

CR-39 solid-state nuclear track detectors are widely used in physics and in many inertial confinement fusion (ICF) experiments, and under ideal conditions these detectors have 100% detection efficiency for ∼0.5-8 MeV protons. When the fluence of incident particles becomes too high, overlap of particle tracks leads to under-counting at typical processing conditions (5 h etch in 6N NaOH at 80 °C). Short etch times required to avoid overlap can cause under-counting as well, as tracks are not fully developed. Experiments have determined the minimum etch times for 100% detection of 1.7-4.3-MeV protons and established that for 2.4-MeV protons, relevant for detection of DD protons, the maximum fluence that can be detected using normal processing techniques is ≲3 × 10(6) cm(-2). A CR-39-based proton detector has been developed to mitigate issues related to high particle fluences on ICF facilities. Using a pinhole and scattering foil several mm in front of the CR-39, proton fluences at the CR-39 are reduced by more than a factor of ∼50, increasing the operating yield upper limit by a comparable amount.

The first experimental demonstration of Rayleigh-Taylor-induced magnetic fields due to the Biermann battery effect has been made. Experiments with laser-irradiated plastic foils were performed to investigate these illusive fields using a monoenergetic proton radiography system. Path-integrated B field strength measurements were inferred from radiographs and found to increase from 10 to 100 T μm during the linear growth phase for 120 μm perturbations. Proton fluence modulations were corrected for Coulomb scattering using measured areal density profiles from x-ray radiographs.

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(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.

Measurements of x-ray-driven implosions with charged particles have resulted in the quantitative characterization of critical aspects of indirect-drive inertial fusion. Three types of spontaneous electric fields differing in strength by two orders of magnitude, the largest being nearly one-tenth of the Bohr field, were discovered with time-gated proton radiographic imaging and spectrally resolved proton self-emission. The views of the spatial structure and temporal evolution of both the laser drive in a hohlraum and implosion properties provide essential insight into, and modeling validation of, x-ray-driven implosions.

A distinctive way of quantitatively imaging inertial fusion implosions has resulted in the characterization of two different types of electromagnetic configurations and in the measurement of the temporal evolution of capsule size and areal density. Radiography with a pulsed, monoenergetic, isotropic proton source reveals field structures through deflection of proton trajectories, and areal densities are quantified through the energy lost by protons while traversing the plasma. The two field structures consist of (i) many radial filaments with complex striations and bifurcations, permeating the entire field of view, of magnetic field magnitude 60 tesla and (ii) a coherent, centrally directed electric field of order 10(9) volts per meter, seen in proximity to the capsule surface. Although the mechanism for generating these fields is unclear, their effect on implosion dynamics is potentially consequential.

Electromagnetic (E/B) fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to inertial confinement fusion have been measured for the first time using novel monoenergetic proton radiography methods. High-resolution, time-gated radiography images of a plastic foil driven by a 10(14) W/cm(2) laser implied B fields of approximately 0.5 MG and E fields of approximately 1.5 x 10(8) V/m. Simulations of these experiments with LASNEX+LSP have been performed and are in overall (though not exact) agreement with the data both for field strengths and for spatial distributions; this is the first direct experimental test of the laser-generated B-field package in LASNEX. The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.

The areal density (rhoR) of D3He filled plastic capsules imploded at OMEGA has been measured at shock coalescence (1.7 ns) and, 400 ps later, during compressive burn, through the energy downshift of 14.7-MeV D3He protons. In this time interval, the azimuthally averaged rhoR changes from 13+/-2.5 to 70+/-8 mg/cm(2). The experiments demonstrate that fuel-shell mix is absent in the central regions at shock coalescence, and that the shell has no holes during compressive burn. We conjecture that rhoR asymmetries measured during compressive burn may be seeded by the time of shock coalescence.