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The time-resolving magnetic recoil spectrometer (MRSt) is a transformative diagnostic that will be used to measure the time-resolved neutron spectrum from an inertial confinement fusion implosion at the National Ignition Facility (NIF). It uses a CD foil on the outside of the hohlraum to convert fusion neutrons to recoil deuterons. An ion-optical system positioned outside the NIF target chamber energy-disperses and focuses forward-scattered deuterons. A pulse-dilation drift tube (PDDT) subsequently dilates, un-skews, and detects the signal. While the foil and ion-optical system have been designed, the PDDT requires more development before it can be implemented. Therefore, a phased plan is presented that first uses the foil and ion-optical systems with detectors that can be implemented immediately—namely CR-39 and hDISC streak cameras. These detectors will allow the MRSt to be commissioned in an intermediate stage and begin collecting data on a reduced timescale, while the PDDT is developed in parallel. A CR-39 detector will be used in phase 1 for the measurement of the time-integrated neutron spectra with excellent energy-resolution, necessary for the energy calibration of the system. Streak cameras will be used in phase 2 for measurement of the time-resolved spectrum with limited spectral coverage, which is sufficient to diagnose the time-resolved ion temperature. Simulations are presented that predict the performance of the streak camera detector, indicating that it will achieve excellent burn history measurements at current yields, and good time-resolved ion-temperature measurements at yields above 3 × 1017. The PDDT will be used for optimal efficiency and resolution in phase 3.

A new Magnetic Recoil Spectrometer (MRSt) is designed to provide time-resolved measurements of the energy spectrum of neutrons emanating from an inertial confinement fusion implosion at the National Ignition Facility. At present, time integrated parameters are being measured using the existing magnet recoil and neutron time-of-flight spectrometers. The capability of high energy resolution of 2 keV and the extension to high time resolution of about 20 ps are expected to improve our understanding of conditions required for successful fusion experiments. The layout, ion-optics, and specifications of the MRSt will be presented.

In the dynamic environment of burning, thermonuclear deuterium–tritium plasmas, diagnosing the time-resolved neutron energy spectrum is of critical importance. Strategies exist for this diagnosis in magnetic confinement fusion plasmas, which presently have a lifetime of ∼1012 longer than inertial confinement fusion (ICF) plasmas. Here, we present a novel concept for a simple, precise, and scale-able diagnostic to measure time-resolved neutron spectra in ICF plasmas. The concept leverages general tomographic reconstruction techniques adapted to time-of-flight parameter space, and then employs an updated Monte Carlo algorithm and National Ignition Facility-relevant constraints to reconstruct the time-evolving neutron energy spectrum. Reconstructed spectra of the primary 14.028 MeV nDT peak are in good agreement with the exact synthetic spectra. The technique is also used to reconstruct the time-evolving downscattered spectrum, although the present implementation shows significantly more error.

Inertial confinement fusion implosions designed to have minimal fluid motion at peak compression often show significant linear flows in the laboratory, attributable per simulations to percent-level imbalances in the laser drive illumination symmetry. We present experimental results which intentionally varied the mode 1 drive imbalance by up to 4% to test hydrodynamic predictions of flows and the resultant imploded core asymmetries and performance, as measured by a combination of DT neutron spectroscopy and high-resolution x-ray core imaging. Neutron yields decrease by up to 50%, and anisotropic neutron Doppler broadening increases by 20%, in agreement with simulations. Furthermore, a tracer jet from the capsule fill-tube perturbation that is entrained by the hot-spot flow confirms the average flow speeds deduced from neutron spectroscopy.

Electron tubes continue to provide the highest speeds possible for recording dynamics of hot high-energy density plasmas. Standard streak camera drive electronics and CCD readout are not compatible with the radiation environment associated with high DT fusion yield inertial confinement fusion experiments >1013 14 MeV DT neutrons or >109 n cm−2 ns−1. We describe a hardened x-ray streak camera developed for the National Ignition Facility and present preliminary results from the first experiment on which it has participated, recording the time-resolved bremsstrahlung spectrum from the core of an inertial confinement fusion implosion at more than 40× the operational neutron yield limit of the previous National Ignition Facility x-ray streak cameras.

A standard technique for generating a burst of hard x rays (above 30 keV) is to use ultra high intensity lasers incident on a target. The strong laser field causes rapid electron oscillations which then generate hard x rays via bremsstrahlung. We have demonstrated a new technique for optimizing the conversion efficiency of laser light to hard x rays at moderate Iλ2 (mid 1013 W/cm2.µm2) assuming that the two plasmon decay plasma instability is the predominant acceleration mechanism. In this scheme, electrons are not directly accelerated by the laser field but by electron plasma waves. Experiments at the National Ignition Facility show the effect of a pre-pulse on the hard x ray spectrum and conversion efficiency. Different experimental configurations are investigated to optimize the conversion efficiency using various pre-pulse levels as well as different target designs (gold vs. silver, varying target thickness, presence of an ablator layer of CH). The conversion efficiency of laser energy into photon above 30 keV for a 100 ps short pulse scales as ∼ I1.23 for laser intensity ranging from 1 × 1016 to 1 × 1017 W/cm2 at 3ω for high Z target. A 1-ns-long pre-pulse pre-seeding an 88-ps Gaussian laser pulse coupled with a CH-coated thin Au target led the highest conversion efficiency above 30 keV of ∼ 3 × 10 − 4 .

Measurement of the neutron spectrum from inertial confinement fusion implosions is one of the primary diagnostics of implosion performance. Analysis of the spectrum gives access to quantities such as neutron yield, hot-spot velocity, apparent ion temperature, and compressed fuel ρr through measurement of the down-scatter ratio. On the National Ignition Facility, the neutron time-of-flight suite has been upgraded to include five independent, collimated lines of sight, each comprising a high dynamic range bibenzyl/diphenylacetylene-stilbene scintillator [R. Hatarik et al., Plasma Fusion Res. 9, 4404104 (2014)] and high-speed fused silica Cherenkov detectors [A. S. Moore et al., Rev. Sci. Instrum. 89, 10I120 (2018)].

We describe a novel technique for measuring bulk fluid motion in materials that is particularly applicable to very hot, x-ray emitting plasmas in the high energy density physics (HEDP) regime. This X-ray Doppler Velocimetry technique relies on monochromatic imaging in multiple closely-spaced wavelength bands near the center of an x-ray emission line in a plasma, and utilizes bent crystals to provide the monochromatic images. Shorter wavelength bands are preferentially sensitive to plasma moving toward the viewer, while longer wavelength bands are preferentially sensitive to plasma moving away from the viewer. Combining multiple images in different wavelength bands allows for reconstruction of the fluid velocity field integrated along the line of sight. Extensions are also possible for absorption geometries, and for three dimensions. We describe the technique, and we present the results of simulations performed to benchmark the viability of the technique for implosion plasma diagnosis.

The Crystal Backlighter Imager (CBI) is a quasi-monochromatic, near-normal incidence, spherically bent crystal imager developed for the National Ignition Facility (NIF), which will allow inertial confinement fusion capsule implosions to be radiographed close to stagnation. This is not possible using the standard pinhole-based area-backlighter configuration, as the self-emission from the capsule hotspot overwhelms the backlighter signal in the final stages of the implosion. The CBI mitigates the broadband self-emission from the capsule hot spot by using the extremely narrow bandwidth inherent to near-normal-incidence Bragg diffraction. Implementing a backlighter system based on near-normal reflection in the NIF chamber presents unique challenges, requiring the CBI to adopt novel engineering and operational strategies. The CBI currently operates with an 11.6 keV backlighter, making it the highest energy radiography diagnostic based on spherically bent crystals to date. For a given velocity, Doppler shift is proportional to the emitted photon energy. At 11.6 keV, the ablation velocity of the backlighter plasma results in a Doppler shift that is significant compared to the bandwidth of the instrument and the width of the atomic line, requiring that the shift be measured to high accuracy and the optics aligned accordingly to compensate. Experiments will be presented that used the CBI itself to measure the backlighter Doppler shift to an accuracy of better than 1 eV. These experiments also measured the spatial resolution of CBI radiographs at 7.0 μm, close to theoretical predictions. Finally, results will be presented from an experiment in which the CBI radiographed a capsule implosion driven by a 1 MJ NIF laser pulse, demonstrating a significant (>100) improvement in the backlighter to self-emission ratio compared to the pinhole-based area-backlighter configuration.

A new ultra-fast photomultiplier tube and associated drivers have been developed for use in the next generation of gamma-ray high pressure gas Cherenkov detectors for inertial confinement fusion experiments at the National Ignition Facility. Pulse-dilation technology has been applied to a standard micro-channel-plate-based photomultiplier tube to improve the temporal response by about 10×. The tube has been packaged suitably for deployment on the National Ignition Facility, and remote electronics have been designed to deliver the required non-linear waveforms to the pulse dilation electrode. This is achieved with an avalanche pulse generator system capable of generating fast arbitrary waveforms over the useful parameter space. The pulse is delivered via fast impedance-matching transformers and isolators, allowing the cathode to be ramped on a sub-nanosecond time scale between two high voltages in a controlled non-linear manner. This results in near linear pulse dilation over several ns. The device has a built-in fiducial system that allows easy calibration and testing with fiber optic laser sources. Results are presented demonstrating the greatly improved response time and other parameters of the device.

The single-line-of-sight, time-resolved x-ray imager (SLOS-TRXI) on OMEGA is one of a new generation of fast-gated x-ray cameras comprising an electron pulse-dilation imager and a nanosecond-gated, burst-mode, hybrid complementary metal-oxide semiconductor sensor. SLOS-TRXI images the core of imploded cryogenic deuterium–tritium shells in inertial confinement fusion experiments in the ∼4- to 9-keV photon energy range with a pinhole imager onto a photocathode. The diagnostic is mounted on a fixed port almost perpendicular to a 16-channel, framing-camera–based, time-resolved Kirkpatrick–Baez microscope, providing a second time-gated line of sight for hot-spot imaging on OMEGA. SLOS-TRXI achieves ∼40-ps temporal resolution and better than 10-μm spatial resolution. Shots with neutron yields of up to 1 × 1014 were taken without observed neutron-induced background signal. The implosion images from SLOS-TRXI show the evolution of the stagnating core.

The Cherenkov mechanism used in Gas Cherenkov Detectors (GCDs) is exceptionally fast. However, the temporal resolution of GCDs, such as the Gamma Reaction History diagnostic at the National Ignition Facility (NIF), has been limited by the current state-of-the-art photomultiplier tube technology to ∼100 ps. The soon-to-be deployed Pulse Dilation Photomultiplier Tube (PD-PMT) at NIF will allow for temporal resolution comparable to that of the gas cell or ∼10 ps. Enhanced resolution will contribute to the quest for ignition in a crucial way through precision measurements of reaction history and ablator areal density (ρR) history, leading to better constrained models. Features such as onset of alpha heating, shock reverberations, and burn truncation due to dynamically evolving failure modes may become visible for the first time. Test measurements of the PD-PMT at Atomic Weapons Establishment confirmed that design goals have been met. The PD-PMT provides dilation factors of 2 to 40× in 6 increments. The GCD-3 recently deployed at the NIF has been modified for coupling to a PD-PMT and will soon be making ultrafast measurements.

Fusion reaction history and ablator areal density measurements for Inertial Confinement Fusion experiments at the National Ignition Facility are currently conducted using the Gamma Reaction History diagnostic (GRH_6m). Future Gas Cherenkov Detectors (GCDs) will ultimately provide ∼100x more sensitivity, reduce the effective temporal response from ∼100 to ∼10 ps, and lower the energy threshold from 2.9 to 1.8 MeV, relative to GRH_6m. The first phase toward next generation GCDs consisted of inserting the existing coaxial GCD-3 detector into a reentrant well which puts it within 4 m of the implosion. Reaction history and ablator gamma measurement results from this Phase I are discussed here. These results demonstrate viability for the follow-on Phases of (II) the use of a revolutionary new pulse-dilation photomultiplier tube to improve the effective measurement bandwidth by >10x relative to current PMT technology; and (III) the design of a NIF-specific "Super" GCD which will be informed by the assessment of the radiation background environment within the well described here.

The time-resolving Magnetic Recoil Spectrometer (MRSt) for the National Ignition Facility (NIF) has been identified by the US National Diagnostic Working Group as one of the transformational diagnostics that will reshape the way inertial confinement fusion (ICF) implosions are diagnosed. The MRSt will measure the time-resolved neutron spectrum of an implosion, from which the time-resolved ion temperature, areal density, and yield will be inferred. Top-level physics requirements for the MRSt were determined based on simulations of numerous ICF implosions with varying degrees of alpha heating, P2 asymmetry, and mix. Synthetic MRSt data were subsequently generated for different configurations using Monte-Carlo methods to determine its performance in relation to the requirements. The system was found to meet most requirements at current neutron yields at the NIF. This work was supported by the DOE and LLNL.

A thin-glass-shell, D3He-filled exploding-pusher inertial confinement fusion implosion at the National Ignition Facility (NIF) has been demonstrated as a proton source that serves as a promising first step toward development of a monoenergetic proton, alpha, and triton backlighting platform at the NIF. Among the key measurements, the D3He-proton emission on this experiment (shot N121128) has been well-characterized spectrally, temporally, and in terms of emission isotropy, revealing a highly monoenergetic ( Δ E / E ∼ 4 % ) and isotropic source (~3% proton fluence variation and ~0.5% proton energy variation). On a similar shot (N130129, with D2 fill), the DD-proton spectrum has been obtained as well, illustrating that monoenergetic protons of multiple energies may be utilized in a single experiment. These results, and experiments on OMEGA, point toward future steps in the development of a precision, monoenergetic proton, alpha, and triton source that can readily be implemented at the NIF for backlighting a broad range of high energy density physics (HEDP) experiments in which fields and flows are manifest, and also utilized for studies of stopping power in warm dense matter and in classical plasmas.

At the completion of the National Ignition Campaign (NIC), the National Ignition Facility (NIF) had about 36 different types of diagnostics. These were based on several decades of development on No...

We report on the first multilocation electron temperature (T_{e}) and flow measurements in an ignition hohlraum at the National Ignition Facility using the novel technique of mid-Z spectroscopic tracer "dots." The measurements define a low resolution "map" of hohlraum plasma conditions and provide a basis for the first multilocation tests of particle and energy transport physics in a laser-driven x-ray cavity. The data set is consistent with classical heat flow near the capsule but reduced heat flow near the laser entrance hole. We evaluate the role of kinetic effects, self-generated magnetic fields, and instabilities in causing spatially dependent heat transport in the hohlraum.

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

Since X-ray diffraction is the definitive method for identifying crystalline phases of a material, it is an important technique for probing high-energy-density materials during laser-driven compression experiments. We are developing a design for collecting several x-ray diffraction datasets during a single laser-driven experiment, with a goal of achieving temporal resolution better than 1 ns. The design combines x-ray streak cameras, for a continuous temporal record of diffraction, with fast x-ray imagers, to collect several diffraction patterns with sufficient solid angle range and resolution to identify crystalline texture. Here we describe the status of the conceptual design, highlighting tradeoffs in the design process.

In inertial confinement fusion (ICF) experiments on the National Ignition Facility (NIF), measurements of average ion temperature using DT neutron time of flight broadening and of DD neutrons do not show the same apparent temperature. Some of this may be due to time and space dependent temperature profiles in the imploding capsule which are not taken into account in the analysis. As such, we are attempting to measure the electron temperature by recording the free-free electron-ion scattering-spectrum from the tail of the Maxwellian temperature distribution. This will be accomplished with the new NIF Continuum Spectrometer (ConSpec) which spans the x-ray range of 20 keV to 30 keV (where any opacity corrections from the remaining mass of the ablator shell are negligible) and will be sensitive to temperatures between ∼ 3 keV and 6 keV. The optical design of the ConSpec is designed to be adaptable to an x-ray streak camera to record time resolved free-free electron continuum spectra for direct measurement of the dT/dt evolution across the burn width of a DT plasma. The spectrometer is a conically bent Bragg crystal in a focusing geometry that allows for the dispersion plane to be perpendicular to the spectrometer axis. Additionally, to address the spatial temperature dependence, both time integrated and time resolved pinhole and penumbral imaging will be provided along the same polar angle. The optical and mechanical design of the instrument is presented along with estimates for the dispersion, solid angle, photometric sensitivity, and performance.

X-ray penumbral imaging has been successfully fielded on a variety of inertial confinement fusion (ICF) capsule implosion experiments on the National Ignition Facility (NIF). We have demonstrated sub-5 μm resolution imaging of stagnated plasma cores (hot spots) at x-ray energies from 6 to 30 keV. These measurements are crucial for improving our understanding of the hot deuterium-tritium fuel assembly, which can be affected by various mechanisms, including complex 3-D perturbations caused by the support tent, fill tube or capsule surface roughness. Here we present the progress on several approaches to improve x-ray penumbral imaging experiments on the NIF. We will discuss experimental setups that include penumbral imaging from multiple lines-of-sight, target mounted penumbral apertures and variably filtered penumbral images. Such setups will improve the signal-to-noise ratio and the spatial imaging resolution, with the goal of enabling spatially resolved measurements of the hot spot electron temperature and material mix in ICF implosions.

We are developing a novel diagnostic for measurement of bulk fluid motion in materials, that is particularly applicable to very hot, x-ray emitting plasmas in the High Energy Density Physics (HEDP) regime. The X-ray Doppler Velocimetry (XDV) technique relies on monochromatic imaging in multiple x-ray energy bands near the center of an x-ray emission line in a plasma, and utilizes bent imaging crystals. Higher energy bands are preferentially sensitive to plasma moving towards the viewer, while lower energy bands are preferentially sensitive to plasma moving away from the viewer. Combining multiple images in different energy bands allows for a reconstruction of the fluid velocity field integrated along the line of sight. We review the technique, and we discuss progress towards benchmarking the technique with proof-of-principle HEDP experiments.

Laser driven inertial confinement fusion (ICF) plasmas typically have burn durations on the order of 100 ps. Time resolved imaging of the x-ray self emission during the hot spot formation is an important diagnostic tool which gives information on implosion symmetry, transient features and stagnation time. Traditional x-ray gated imagers for ICF use microchannel plate detectors to obtain gate widths of 40-100 ps. The development of electron pulse-dilation imaging has enabled a 10X improvement in temporal resolution over legacy instruments. In this technique, the incoming x-ray image is converted to electrons at a photocathode. The electrons are accelerated with a time-varying potential that leads to temporal expansion as the electron signal transits the tube. This expanded signal is recorded with a gated detector and the effective temporal resolution of the composite system can be as low as several picoseconds. An instrument based on this principle, known as the Dilation X-ray Imager (DIXI) has been constructed and fielded at the National Ignition Facility. Design features and experimental results from DIXI will be presented.

Current inertial confinement fusion experiments on the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)] are attempting to demonstrate thermonuclear ignition using x-ray drive by imploding spherical targets containing hydrogen-isotope fuel in the form of a thin cryogenic layer surrounding a central volume of fuel vapor [J. Lindl, Phys. Plasmas 2, 3933 (1995)]. The fuel is contained within a plastic ablator layer with small concentrations of one or more mid-Z elements, e.g., Ge or Cu. The capsule implodes, driven by intense x-ray emission from the inner surface of a hohlraum enclosure irradiated by the NIF laser, and fusion reactions occur in the central hot spot near the time of peak compression. Ignition will occur if the hot spot within the compressed fuel layer attains a high-enough areal density to retain enough of the reaction product energy to reach nuclear reaction temperatures within the inertial hydrodynamic disassembly time of the fuel mass ...

An optical Thomson scattering diagnostic has been designed for the National Ignition Facility to characterize under-dense plasmas. We report on the design of the system and the expected performance for different target configurations. The diagnostic is designed to spatially and temporally resolve the Thomson scattered light from laser driven targets. The diagnostic will collect scattered light from a 50 × 50 × 200 μm volume. The optical design allows operation with different probe laser wavelengths. A deep-UV probe beam (λ0 = 210 nm) will be used to Thomson scatter from electron plasma densities of ∼5 × 1020 cm−3 while a 3ω probe will be used for plasma densities of ∼1 × 1019 cm−3. The diagnostic package contains two spectrometers: the first to resolve Thomson scattering from ion acoustic wave fluctuations and the second to resolve scattering from electron plasma wave fluctuations. Expected signal levels relative to background will be presented for typical target configurations (hohlraums and a planar foil).

The National Ignition Facility (NIF) is a 192 laser beam facility designed to support the Stockpile Stewardship, High Energy Density and Inertial Confinement Fusion (ICF) programs. We report on the design of an Optical Thomson Scattering (OTS) diagnostic that has the potential to transform the community’s understanding of NIF hohlraum physics by providing first principle, local, time-resolved measurements of under-dense plasma conditions. The system design allows operation with different probe laser wavelengths by manual selection of the appropriate beam splitter and gratings before the shot. A deep-UV probe beam (λ0-210 nm) will be used to optimize the scattered signal for plasma densities of 5 × 1020 electrons/cm3 while a 3ω probe will be used for experiments investigating lower density plasmas of 1 × 1019 electrons/cm3. We report the phase I design of a two phase design strategy. Phase I includes the OTS telescope, spectrometer, and streak camera; these will be used to assess the background levels at NIF. Phase II will include the design and installation of a probe laser.

A Magnetic Recoil Spectrometer (MRSt) has been conceptually designed for time-resolved measurements of the neutron spectrum at the National Ignition Facility. Using the MRSt, the goals are to measure the time-evolution of the spectrum with a time resolution of ∼20-ps and absolute accuracy better than 5%. To meet these goals, a detailed understanding and optimization of the signal and background characteristics are required. Through ion-optics, MCNP simulations, and detector-response calculations, it is demonstrated that the goals and a signal-to background >5–10 for the down-scattered neutron measurement are met if the background, consisting of ambient neutrons and gammas, at the MRSt is reduced 50–100 times.

We report simulations and experiments that demonstrate an increase in spatial resolution of the NIF core diagnostic x-ray streak cameras by at least a factor of two, especially off axis. A design was achieved by using a corrector electron optic to flatten the field curvature at the detector plane and corroborated by measurement. In addition, particle in cell simulations were performed to identify the regions in the streak camera that contribute the most to space charge blurring. These simulations provide a tool for convolving synthetic pre-shot spectra with the instrument function so signal levels can be set to maximize dynamic range for the relevant part of the streak record.

Current two-dimensional X-ray imaging at the National Ignition Facility (NIF) uses time resolved pinhole cameras with ∼10-25 μm pinholes. This method has limitations in the smallest resolvable features that can be imaged with reasonable photon statistics for inertial confinement fusion (ICF) applications. ICF sources have a broadband self-emission spectrum that causes the pinhole images obtained, through thin foil filters, to contain a similarly broadband spectrum complicating the interpretation of structure in the source. In order to study phenomena on the scale of ∼5 μm, such as dopant mix in the ICF capsule, a narrow energy band, higher spatial resolution microscope system with improved signal/noise has been developed using X-ray optics. Utilizing grazing incidence mirrors in a Kirkpatrick-Baez microscope (KBM) configuration [P. Kirkpatrick and A. V. Baez, J. Opt. Soc. Am. 38, 766–774 (1948)], an X-ray microscope has been designed and fielded on NIF with four imaging channels. The KBM has ∼12 × magnification

Indirect drive converts high power laser light into x-rays using small high-Z cavities called hohlraums. X-rays generated at the hohlraum walls drive a capsule filled with deuterium–tritium (DT) fuel to fusion conditions. Recent experiments have produced fusion yields exceeding 50 kJ where alpha heating provides ~3× increase in yield over PdV work. Closing the gaps toward ignition is challenging, requiring optimization of the target/implosions and the laser to extract maximum energy. The US program has a three-pronged approach to maximize target performance, each closing some portion of the gap. The first item is optimizing the hohlraum to couple more energy to the capsule while maintaining symmetry control. Novel hohlraum designs are being pursued that enable a larger capsule to be driven symmetrically to both reduce 3D effects and increase energy coupled to the capsule. The second issue being addressed is capsule stability. Seeding of instabilities by the hardware used to mount the capsule and fill it with DT fuel remains a concern. Work reducing the impact of the DT fill tubes and novel capsule mounts is being pursed to reduce the effect of mix on the capsule implosions. There is also growing evidence native capsule seeds such as a micro-structure may be playing a role on limiting capsule performance and dedicated experiments are being developed to better understand the phenomenon. The last area of emphasis is the laser. As technology progresses and understanding of laser damage/mitigation advances, increasing the laser energy seems possible. This would increase the amount of energy available to couple to the capsule, and allow larger capsules, potentially increasing the hot spot pressure and confinement time. The combination of each of these focus areas has the potential to produce conditions to initiate thermo-nuclear ignition.

Collisional kinetic modifications of ion distributions in interpenetrating flows are investigated by irradiating two opposing targets, either CD/CD or CD/CH, on the National Ignition Facility. In the CD/CD case, neutron time-of-flight diagnostics are successfully used to infer the ion temperature, 5–6 keV, and velocity, 500 km/s per flow, of the flows using a multi-fluid approximation of beam-beam nuclear fusion. These values are found to be in agreement with simulations and other diagnostics. However, for CD/CH, the multi-fluid assumption breaks down, as fusion is quasi-thermonuclear in this case and thus more dependent on the details of the ion velocity distribution. Using kinetic-ion, hydrodynamic-electron, and hybrid particle-in-cell modeling, this is found to be partially due to a skewed deviation from a Maxwellian in the ion velocity distribution function resulting from ion-ion collisions. This skew causes a downshift in the mean neutron velocity that partially resolves the observation in the CD/CH case. We note that the discrepancy is not completely resolved via collisional effects alone and may be a signature of collisionless electromagnetic interactions such as the Weibel-filamentation instability.

A new generation of fast-gated x-ray framing cameras have been developed that are capable of capturing multiple frames along a single line-of-sight with 30 ps temporal resolution. The instruments are constructed by integrating pulse-dilation electron imaging with burst mode hybrid-complimentary metal-oxide-semiconductor sensors. Two such instruments have been developed, characterized, and fielded at the National Ignition Facility and the OMEGA laser. These instruments are particularly suited for advanced x-ray imaging applications in Inertial Confinement Fusion and High energy density experiments. Here, we discuss the system architecture and the techniques required for tuning the instruments to achieve optimal performance. Characterization results are also presented along with planned future improvements to the design.

A high resolution, Diagnostic Instrument Manipulator (DIM)-based x-ray Bragg crystal spectrometer has been calibrated for and deployed at the National Ignition Facility (NIF) to diagnose plasma conditions in ignition capsules near stagnation times. The spectrometer has two conical crystals in the Hall geometry focusing rays from the Kr Heα, Lyα, and Heβ complexes onto a streak camera, with the physics objectives of measuring time-resolved electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. A third von Hamos crystal that time-integrates the Kr Heα, Heβ and intervening energy range provides in situ calibration for the streak camera signals. The spectrometer has been absolutely calibrated using a microfocus x-ray source, an array of CCD and single-photon-counting detectors, and multiple K- and L-absorption edge filters at the Princeton Plasma Physics Laboratory (PPPL) x-ray laboratory. Measurements of the integrated reflectivity, energy range, and energy resolution for each crystal are discussed. These calibration data provide absolute x-ray signal levels for NIF measurements, enabling precise filter selection and comparisons to simulations.

A new capability at the National Ignition Facility (NIF) has been implemented to measure the temperature of x-ray emitting sources. Although it is designed primarily for Inertial Confinement Fusion (ICF), it can be used for any hot emitting source that is well modeled. The electron temperature (Te) of the hot spot within the core of imploded ICF capsules is an effective indicator of implosion performance. Currently, there are spatially and temporally integrated Te inferences using image plates. A temporally resolved measurement of Te will help elucidate the mechanisms for hot spot heating and cooling such as conduction to fuel, alpha-heating, mix, and radiative losses. To determine the temporally resolved Te of hot spots, specific filters are added to an existing x-ray streak camera "streaked polar instrumentation for diagnosing energetic radiation" to probe the emission spectrum during the x-ray burn history of implosions at the NIF. One of the difficulties in inferring the hot spot temperature is the attenuation of the emission due to opacity from the shell and fuel. Therefore, a series of increasingly thick titanium filters were implemented to isolate the emission in specific energy regions that are sensitive to temperatures above 3 keV while not significantly influenced by the shell/fuel attenuation. Additionally, a relatively thin zinc filter was used to measure the contribution of colder emission sources. Since the signal levels of the emission through the thicker filters are relatively poor, a dual slit (aperture) was designed to increase the detected signal at the higher end of the spectrum. Herein, the design of the filters and slit is described, an overview of the solving technique is provided, and the initial electron temperature results are reported.

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_{ion} are inferred from the variance of the primary neutron spectrum. Consistently higher DT than DD T_{ion} are observed and the difference is seen to increase with increasing apparent DT T_{ion}. The line-of-sight rms variations of both DD and DT T_{ion} are small, ∼150eV, indicating an isotropic source. The DD neutron yields are consistently high relative to the DT neutron yields given the observed T_{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_{ion} greater than the DD T_{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.

A demonstration of the ability to control the flow of laser energy in a dense plasma by tuning the colour of multiple laser beams injected into it could be useful in the development of laser-driven fusion.

The National Ignition Facility (NIF) is capable of creating new and novel high-energy-density (HED) systems relevant to astrophysics. Specifically, a system could be created that studies the effects of a radiative shock on a hydrodynamically unstable interface. These dynamics would be relevant to the early evolution after a core-collapse supernova of a red supergiant star. Prior to NIF, no HED facility had enough energy to perform this kind of experiment. The experimental target will include a 340 μm predominantly plastic ablator followed by a low-density SiO2 foam. The interface will have a specific, machined pattern that will seed hydrodynamic instabilities. The growth of the instabilities in a radiation-dominated environment will be observed. This experiment requires a ≥300 eV hohlraum drive and will be diagnosed using point projection pinhole radiography, which have both been recently demonstrated on NIF.

A pulse-dilation photomultiplier tube (PD-PMT) with sub-20 ps temporal resolution has been developed for use with γ-ray-sensitive gas Cherenkov detectors at the National Ignition Facility to improve the diagnosis of nuclear fusion burn history and the areal density of the remaining capsule ablator. The pulse-dilation mechanism entails the application of a time-dependent, ramp waveform to a photocathode-mesh structure, introducing a time-dependent photoelectron accelerating potential. The electric field imparts axial velocity dispersion to outgoing photoelectrons. The photoelectron pulse is dilated as it transits a drift region prior to amplification in a microchannel plate and read out with a digital oscilloscope. We report the first measurements with the prototype PD-PMT demonstrating nominal

Ignition Set to Go One aim of the National Ignition Facility is to implode a capsule containing a deuterium-tritium fuel mix and initiate a fusion reaction. With 192 intense laser beams focused into a centimeter-scale cavity, a major challenge has been to create a symmetric implosion and the necessary temperatures within the cavity for ignition to be realized (see the Perspective by Norreys ). Glenzer et al. (p. 1228 , published online 28 January) now show that these conditions can be met, paving the way for the next step of igniting a fuel-filled capsule. Furthermore, Li et al. (p. 1231 , published online 28 January) show how charged particles can be used to characterize and measure the conditions within the imploding capsule. The high energies and temperature realized can also be used to model astrophysical and other extreme energy processes in a laboratory settings.

Ignition Set to Go One aim of the National Ignition Facility is to implode a capsule containing a deuterium-tritium fuel mix and initiate a fusion reaction. With 192 intense laser beams focused into a centimeter-scale cavity, a major challenge has been to create a symmetric implosion and the necessary temperatures within the cavity for ignition to be realized (see the Perspective by Norreys ). Glenzer et al. (p. 1228 , published online 28 January) now show that these conditions can be met, paving the way for the next step of igniting a fuel-filled capsule. Furthermore, Li et al. (p. 1231 , published online 28 January) show how charged particles can be used to characterize and measure the conditions within the imploding capsule. The high energies and temperature realized can also be used to model astrophysical and other extreme energy processes in a laboratory settings.

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ~ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 X 10¹⁵ neutrons, with 20% calculated alpha heating at convergence ~27X.

Experiments have recently been conducted at the National Ignition Facility utilizing inertial confinement fusion capsule ablators that are 175 and 165 μm in thickness, 10% and 15% thinner, respectively, than the nominal thickness capsule used throughout the high foot and most of the National Ignition Campaign. These three-shock, high-adiabat, high-foot implosions have demonstrated good performance, with higher velocity and better symmetry control at lower laser powers and energies than their nominal thickness ablator counterparts. Little to no hydrodynamic mix into the DT hot spot has been observed despite the higher velocities and reduced depth for possible instability feedthrough. Early results have shown good repeatability, with up to 1/2 the neutron yield coming from α-particle self-heating.

Direct-drive inertial confinement fusion (ICF) is expected to demonstrate high gain on the National Ignition Facility (NIF) in the next decade and is a leading candidate for inertial fusion energy production. The demonstration of high areal densities in hydrodynamically scaled cryogenic DT or D2 implosions with neutron yields that are a significant fraction of the “clean” 1-D predictions will validate the ignition-equivalent direct-drive target performance on the OMEGA laser at the Laboratory for Laser Energetics (LLE). This paper highlights the recent experimental and theoretical progress leading toward achieving this validation in the next few years. The NIF will initially be configured for X-ray drive and with no beams placed at the target equator to provide a symmetric irradiation of a direct-drive capsule. LLE is developing the “polar-direct-drive” (PDD) approach that repoints beams toward the target equator. Initial 2-D simulations have shown ignition. A unique “Saturn-like” plastic ring around the equator refracts the laser light incident near the equator toward the target, improving the drive uniformity. LLE is currently constructing the multibeam, 2.6-kJ/beam, petawatt laser system OMEGA EP. Integrated fast-ignition experiments, combining the OMEGA EP and OMEGA Laser Systems, will begin in FY08.

Recently developed diagnostic techniques at LLNL require recording backlit images of extremely dense imploded plasmas using hard x-rays, and demand the detector to be sensitive to photons with energies higher than 50 keV [R. Tommasini et al., Phys. Phys. Plasmas 18, 056309 (2011); G. N. Hall et al., “AXIS: An instrument for imaging Compton radiographs using ARC on the NIF,” Rev. Sci. Instrum. (these proceedings)]. To increase the sensitivity in the high energy region, we propose to use a combination of two MCPs. The first MCP is operated in a low gain regime and works as a thick photocathode, and the second MCP works as a high gain electron multiplier. We tested the concept of this dual MCP configuration and succeeded in obtaining a detective quantum efficiency of 4.5% for 59 keV x-rays, 3 times larger than with a single plate of the thickness typically used in NIF framing cameras.

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ∼1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in the filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±

Significant theoretical and experimental progress continues to be made at the University of Rochester's Laboratory for Laser Energetics (LLE), charting the path to direct-drive inertial confinement fusion (ICF) ignition. Direct drive offers the potential for higher-gain implosions than x-ray drive and is a leading candidate for an inertial fusion energy power plant. LLE's direct-drive ICF ignition target designs for the National Ignition Facility (NIF) are based on hot-spot ignition. A cryogenic target with a spherical DT-ice layer, within or without a foam matrix, enclosed by a thin plastic shell, will be directly irradiated with ~1.5 MJ of laser energy. Cryogenic and plastic/foam (surrogate-cryogenic) targets that are hydrodynamically scaled from these ignition target designs are imploded on the 60-beam, 30 kJ, UV OMEGA laser system to validate the key target physics issues, including energy coupling, hydrodynamic instabilities and implosion symmetry. Prospects for direct-drive ignition on the NIF are extremely favourable, even while it is in its x-ray-drive irradiation configuration, with the development of the polar-direct-drive concept. A high-energy petawatt capability is being constructed at LLE next to the existing 60-beam OMEGA compression facility. This OMEGA EP (extended performance) laser will add two short-pulse, 2.6 kJ beams to the OMEGA laser system to backlight direct-drive ICF implosions and study fast-ignition physics with focused intensities up to 6 × 1020 W cm−2.

Three recent developments in direct-drive target design have enhanced the possibility of achieving high target gain on the National Ignition Facility (NIF): (1) Laser absorption was increased by almost 50% using wetted-foam targets. (2) Adiabat shaping significantly increased the hydrodynamic stability of the target during the acceleration phase of the implosion without sacrificing target gain. (3) Techniques to reduce laser imprint using pulse shaping and radiation preheat were developed. These design features can be employed for direct-drive-ignition experiments while the NIF is in the x-ray-drive configuration. This involves repointing some of the beams toward the equator of the target to improve uniformity of target drive. This approach, known as polar direct drive (PDD), will enhance the capability of the NIF to explore ignition conditions. PDD will couple more energy to the fuel than x-ray drive. The compressed fuel core can be more easily accessed for high-ρR diagnostic development and for fast-ign...