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BackgroundThe optimal strategy of weaning veno-arterial (V-A) extracorporeal membrane oxygenation (ECMO) remains poorly described. Pump-controlled retrograde trial off (PCRTO) involves serial decremental pump revolutions until a retrograde flow from the arterial to venous ECMO cannula is achieved. It has been reported as a feasible weaning strategy in the pediatric population, but its application in adults has not been widely reported.MethodsThis was a retrospective observational study including all adult patients who underwent PCRTO during weaning from V-A ECMO at a tertiary ECMO center between January 2019 and July 2021. Hemodynamic characteristics during PCRTO and clinical outcomes were reported. The clinical and echocardiographic parameters of successful and unsuccessful PCRTO runs were compared.Results A total of 57 runs of PCRTO in 36 patients were analyzed – 45 (78.9%) of the trials were successful. The median blood flow rate during PCRTO was 0.6 L/min, and the median duration of PCRTO was 240 minutes in the successful group compared with 35 minutes in the unsuccessful group. Patients who tolerated the trial had higher systolic blood pressure (105 vs 96 mmHg, p=0.042) and mean arterial pressure (78 vs 63 mmHg, p=0.008) at the end of PCRTO. The left ventricular outflow tract velocity-time integral measured during PCRTO was greater in the successful group (17.5 vs 12.9 cm, p=0.021).Of the 35 patients who had at least one session of successful PCRTO, 31 (88.6%) ultimately underwent ECMO decannulation. In adjusted analysis, baseline alanine aminotransferase (OR 8.16, 95% CI 1.31-50.9, p=0.025) and serum creatinine (OR 7.15, 95% CI 1.04-49.2, p=0.046) were significantly associated with increased probability of successful PCRTO.ConclusionsPCRTO is a feasible strategy for trialing off V-A ECMO with a low risk of adverse events and high rate of predicting eventual successful ECMO decannulation. Laboratory parameters that reflect the degree and recovery of end-organ ischemic injury were useful for predicting a successful PCRTO. The application of PCRTO should be studied in multi-centered studies.

An optical diagnostic based on resonant absorption of laser light in a plasma is introduced and is used for the determination of density scale lengths in the range of 10 nm to >1 μm at the critical surface of an overdense plasma. This diagnostic is also used to extract the plasma collisional frequency, allowing inference of the temporally evolving plasma composition on the tens of femtosecond timescale. This is found to be characterized by two eras: the early time and short scale length expansion (L 0.1λ); this is consistent with a hydrogen plasma decoupling from the bulk target material. Density gradients and plasma parameters on this scale are of importance to plasma mirror optical performance and comment is made on this theme.

The authors show that plasma electrons under petawatt laser light exhibit a random walk in a self-generated field resulting in electron confinement and efficient ion acceleration.

Rep-rated diagnostics are a necessity for present and future laser facilities focused on the study of high-energy-density (HED) phenomena. Electromagnetic fields in HED systems are of particular interest to the community, but are inherently difficult to diagnose due to the high mass-densities involved. By utilizing high-energy protons that penetrate through dense plasmas, fields may be visualized by detecting variations in proton fluence caused by the Lorenz interaction of the protons with the field. Typical detecting media used for proton imaging are single-use and do not scale well to rep-rated operation. We propose here the use of a scintillator-based detector and characterize the energy and spatial responses to demonstrate its feasibility as a viable option for rep-rated proton imaging and other diagnostics.

As high-intensity short-pulse lasers that can operate at high-repetition-rate (HRR) (>10 Hz) come online around the world, the high-energy-density (HED) science they enable will experience a radical paradigm shift. The >10^3x increase in shot rate over today’s shot-per-hour drivers translates into dramatically faster data acquisition and more experiments, and thus the potential to significantly accelerate the advancement of HED science. We will present the vision and ongoing work to realize a HRR framework that allows for rapidly delivered optimal experiments by bringing together feedback laser control loops, high-throughput targetry and diagnostics, cognitive simulation, enhanced HED codes, and advanced data analytics.

Application of deep learning to shaped, short-pulse laser-driven ion acceleration. Using a neural network as a universal approximator function, i.e., a surrogate model, we can map out large areas of parameter space. The neural network is informed by a large dataset of about 1,000, mid-fidelity particle-in-cell simulations modeling instances of Target-Normal Sheath Acceleration. The neural-network-based function allows us to rapidly explore regions of interest in search of optimal input parameters and features of interest.

High intensity, high-repetition rate (HRR) lasers, that is lasers that can operate on the order of 1 Hz or faster, are quickly coming on-line around the world. High intensity lasers have long been an impactful tool in high energy density (HED) science since they are capable of creating matter at extreme temperatures and pressures relevant to this field. The advent of HRR technology enhances to this capability since HRR enables these types of these experiments to be performed faster, thus leading to an acceleration in the rate of learning in fundamental HED science. However, in order to use the full potential of HRR systems, high repetition rate diagnostics in addition to real-time analysis tools must be developed to process experimental measurements and outputs at a rate that matches the laser. Towards this goal, we present an automated machine learning based analysis for a synthetic X-ray spectrometer, which is a common diagnostic in HED experiments.

This work examines pulses with orbital angular momentum and simulates the characterization of these pulses using STRIPED FISH, which correctly retrieves optical vortices and can be leveraged to provide deeper insight into laser plasma interactions.

The impact to fusion energy production due to the radiative loss from a localized mix in inertial confinement implosions using high density carbon capsule targets has been quantified. The radiative loss from the localized mix and local cooling of the reacting plasma conditions was quantified using neutron and x-ray images to reconstruct the hot spot conditions during thermonuclear burn. Such localized features arise from ablator material that is injected into the hot spot from the Rayleigh-Taylor growth of capsule surface perturbations, particularly the tube used to fill the capsule with deuterium and tritium fuel. Observations, consistent with analytic estimates, show the degradation to fusion energy production to be linearly proportional to the fraction of the total emission that is associated with injected ablator material and that this radiative loss has been the primary source of variations, of up to 1.6 times, in observed fusion energy production. Reducing the fill tube diameter has increased the ignition metric ${\ensuremath{\chi}}_{\mathrm{no}\text{ }\ensuremath{\alpha}}$ from 0.49 to 0.72, 92% of that required to achieve a burning hot spot.

Relativistic electron temperatures were measured from kilojoule, subrelativistic laser-plasma interactions. Experiments show an order of magnitude higher temperatures than expected from a ponderomotive scaling, where temperatures of up to 2.2 MeV were generated using an intensity of 1×10^{18}W/cm^{2}. Two-dimensional particle-in-cell simulations suggest that electrons gain superponderomotive energies by stochastic acceleration as they sample a large area of rapidly changing laser phase. We demonstrate that such high temperatures are possible from subrelativistic intensities by using lasers with long pulse durations and large spatial scales.

High-intensity short-pulse lasers are being pushed further as applications continue to demand higher laser intensities. Uses such as radiography and laser-driven particle acceleration require these higher intensities to produce the necessary x-ray and particle fluxes. Achieving these intensities, however, is limited by the damage threshold of costly optics and the complexity of target chambers. This is evidenced by the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory, producing four high-energy ≈ 1 k J laser pulses at 30 ps pulse duration, being limited to an intensity of 10 18 W / c m 2 by the large focal spot size of ≈ 100 µ m . Due to the setup complexity of NIF, changing the location of the final focusing parabola in order to improve the focal spot size is not an option. This leads to the possible use of disposable ellipsoidal plasma mirrors (PMs) placed within the chamber, close to the target in an attempt to refocus the four ARC beams. However, the behavior of PMs at these relatively long pulse durations (tens of picoseconds) is not well characterized. The results from the COMET laser at the Jupiter Laser Facility carried out at 0.5 to 20 ps pulse durations on flat mirrors are presented as a necessary first step towards focusing curved mirrors. The findings show defocusing at longer pulse durations and higher intensities, with less degradation when using aluminum coated mirrors.

A single shot, complete spatiotemporal measurement of the complex electric field E(x,y,z,t) emitted by a high power (>0.1 TW) laser is demonstrated for the first time. Color movies of the laser's electric field are retrieved, and the temporal, spectral, and spatial field features are examined.

1. Introduction One of the most studied short-pulse laser-driven particle acceleration schemes is proton generation via the target-normal sheath-acceleration[1] mechanism, where hundreds of experiments[2] have been performed at facilities worldwide. This acceleration mechanism relies on the production of MeV energy electrons from the laser interaction with the target in order to produce 10’s of MeV proton energies. To date, most short-pulse experiments have been performed with single Gaussian-like pulses that are often not well characterized in terms of pulse-length and time-dependent intensity. This is in contrast to nanosecond-scale laser pulses that utilize pulse shaping technique to deliver precise pulse shapes for manipulating time-dependent physics. Such pulse shaping has allowed access to novel physics such as in Inertial Confinement Fusion (ICF) [3] and Equation of State (EOS) [4] experiments. It has similarly allowed for increased efficiency of laser-driven x-ray [5] and particle (proton or neutron) sources [6]. Multiple methods for generating custom pulse shapes at the sub-picosecond level already exist but are rarely employed for high-intensity laser-driven experiments. These methods include combining separate short-pulse beams, splitting and recombining single pulses, interferometric methods [7], or spectral shaping [8]. A limited number of experiments with some form of pulse shaping for high-intensity lasers have shown significant spectral enhancements to secondary sources such as MeV proton beams[9], implying that controlled manipulation of time-dependent particle acceleration physics is possible at the fs to ps level.

The mode-1 x-ray drive asymmetry of indirect-drive Inertial Confinement Fusion(ICF) implosions at the National Ignition Facility(NIF) has been estimated using a simple static ViewFactor model. The model takes as input measured laser performance data in the foot and peak, the hohlraum configuration, and laser to hohlraum pointing. These estimates are compared with neutron time-of-flight measurements of directionality and magnitude of the resultant hotspot bulk velocity (~20–100 μm/ns) for 39 NIF shots using High Density Carbon (HDC) ablators and show strong correlation on a statistically significant number of shots. The most important factors identified so far are random quad-to-quad peak power laser imbalances, the presence of lossy diagnostic windows and gaps on the hohlraum waist, capsule sag and capsule thickness mode 1. Typical mode-1 asymmetry in drive is currently ~0.5% for many of these sources on their own and, when summed, can lead to a neutron hotspot velocity of up to 100 μm /ns and a reduction in yield of 35% for current NIF DT layered implosions. Our goal is to identify, quantify and mitigate all potential sources of mode-1 asymmetry (which also include target and laser alignment imperfections, foot power and Cross Beam Energy Transfer imbalances) to enable higher quality implosions on NIF.

We present a deep learning based framework for real-time analysis of a differential filter based x-ray spectrometer that is common on short-pulse laser experiments. The analysis framework was trained with a large repository of synthetic data to retrieve key experimental metrics, such as slope temperature. With traditional analysis methods, these quantities would have to be extracted from data using a time-intensive and manual analysis. This framework was developed for a specific diagnostic, but may be applicable to a wide variety of diagnostics common to laser experiments and thus will be especially crucial to the development of high-repetition rate (HRR) diagnostics for HRR laser systems that are coming online.

Nuclear reactions taking place in stars are not straightforward to study in laboratories on Earth. Now, inertial-confinement fusion implosion experiments are reported that mimic the conditions for the hydrogen-burning phase in main-sequence stars.

One of the pressing demands in our western society is the safety and maintenance of our nuclear legacy. In Germany the dismantling, safe processing and storage of nuclear waste have resulted in a multi-national research program. One of the findings was that nondestructive testing methods and material selective imaging of compound large objects is possible using thermal and fast neutrons. They also identified that a powerful, safe, and compact neutron source would be required. Since the advent of ultra-intense lasers many applications have been investigated using the unique parameter of laser-driven secondary sources. Recently, we have demonstrated the realization of a short-pulse laser- driven neutron source with beam intensities orders of magnitude above earlier attempts. Those sources can lead to a compact and potentially mobile neutron source with a large number of applications. The neutron source is based on a so-called pitcher-catcher approach, where a short burst of energetic, laser-driven deuteron ions are converted into a short pulse of neutrons in a subsequent converter material. Here, in addition to neutron conversion via (d,n) reactions the breakup of energetic deuterons and a non-thermal pre-compound reaction in the converter material result in a directed beam of neutrons and an increase in neutron numbers compared to earlier attempts. The neutron record number so far were produced using high-contrast, high-energy short pulse lasers of a few hundred femtosecond pulse duration and invoking relativistic transparency in solids as a new ion acceleration mechanism. I will present the underlying mechanism of creating an intense pulsed and highly directed beam of neutrons using ultra-intense lasers and the recent experimental results using laser systems in the US and in Europe. Furthermore, I will focus on a few examples of using such sources for applications that are either important for the security of our countries or will have large economical potential in industrial applications. These range from the remote sensing of illicit nuclear material in cargo to the non-destructive analysis of large civil constructions using compact laser systems. The initial ion pulse that is converted into neutrons is of only a few picosecond duration and thus the neutron burst is generated with sub-nanosecond pulse length. This allows for precise energy resolution of the neutrons using time-of flight techniques. As the ion acceleration is of only a few millimeter in length, replacing ten's to hundred's of meter of conventional acceleration length the source is extremely compact. As the ion beams are extremely intense and do not suffer from space charge deterioration the fast neutron source is capable of point projection imaging with an initial source size of around a millimeter. As the pulse duration is short, high energy resolution can be achieved at a much reduced time-of-flight length offering more compact systems. As future laser systems largely increase not only peak power, but also already offer repetition rates up the kHz applications in research and industry become visible. To fully take advantage of those new sources new detector systems should keep up with enhanced spatial and temporal resolution. Also they need to withstand the unavoidable x-ray flash and electro-magnetic pulse originating from the laser plasma interaction. We have started to explore novel detectors and tested them at high-energy short pulse laser systems for fast and thermal neutron beams.

This paper presents a study on hotspot parameters in indirect-drive, inertially confined fusion implosions as they proceed through the self-heating regime. The implosions with increasing nuclear yield reach the burning-plasma regime, hotspot ignition, and finally propagating burn and ignition. These implosions span a wide range of alpha heating from a yield amplification of 1.7-2.5. We show that the hotspot parameters are explicitly dependent on both yield and velocity and that by fitting to both of these quantities the hotspot parameters can be fit with a single power law in velocity. The yield scaling also enables the hotspot parameters extrapolation to higher yields. This is important as various degradation mechanisms can occur on a given implosion at fixed implosion velocity which can have a large impact on both yield and the hotspot parameters. The yield scaling also enables the experimental dependence of the hotspot parameters on yield amplification to be determined. The implosions reported have resulted in the highest yield (1.73×10^{16}±2.6%), yield amplification, pressure, and implosion velocity yet reported at the National Ignition Facility.

We present direct measurements of electron temperature variations within an inertially confined deuterium-tritium plasma caused by localized mix of higher-Z materials into the central hot spot. The data are derived from newly developed differentially filtered penumbral imaging of the bremsstrahlung continuum emission. Our analysis reveals distinct localized emitting features in the stagnated hot-spot plasma, and we infer spatial variations in the electron temperature: the mixed region is 660±130eV colder than the surrounding hot-spot plasma at 3.26±0.11keV. Our analysis of the energy flow shows that we measure approximately steady-state conditions where the radiative losses in the mix region are balanced by heat conduction from the surrounding hot deuterium-tritium plasma.

New short-pulse kilojoule, Petawatt-class lasers, which have recently come online and are coupled to large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting tools to capture transformational science opportunities in high energy density physics. These short-pulse lasers also happen to reside in a unique laser regime: very high-energy (kilojoule), relatively long (multi-picosecond) pulse-lengths, and large (10s of micron) focal spots, where their use in driving energetic particle beams is largely unexplored. Proton acceleration via Target Normal Sheath Acceleration (TNSA) using the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility in the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 18 MeV are measured using laser irradiation of >1 ps pulse-lengths and quasi-relativistic (∼1018 W/cm2) intensities. This is indicative of a super-ponderomotive electron acceleration mechanism that sustains acceleration over long (multi-picosecond) time-scales and allows for proton energies to be achieved far beyond what the well-established scalings of proton acceleration via TNSA would predict at these modest intensities. Furthermore, the characteristics of the ARC laser (large ∼100 μm diameter focal spot, flat spatial profile, multi-picosecond, relatively low prepulse) provide acceleration conditions that allow for the investigation of 1D-like particle acceleration. A high flux ∼ 50 J of laser-accelerated protons is experimentally demonstrated. A new capability in multi-picosecond particle-in-cell simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-picosecond particle acceleration.

Developments in machine learning promise to ameliorate some of the challenges of modeling complex physical systems through neural-network-based surrogate models. High-intensity, short-pulse lasers can be used to accelerate ions to mega-electronvolt energies, but to model such interactions requires computationally expensive techniques such as particle-in-cell simulations. Multilayer neural networks allow one to take a relatively sparse ensemble of simulations and generate a surrogate model that can be used to rapidly search the parameter space of interest. In this work, we created an ensemble of over 1,000 simulations modeling laser-driven ion acceleration and developed a surrogate to study the resulting parameter space. A neural-network-based approach allows for rapid feature discovery not possible for traditional parameter scans given the computational cost. A notable observation made during this study was the dependence of ion energy on the pre-plasma gradient length scale. While this methodology harbors great promise for ion acceleration, it has ready application to all topics in which large-scale parameter scans are restricted by significant computational cost or relatively large, but sparse, domains.

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.

Current capsule implosions at the National Ignition Facility (NIF) using high-density-carbon ablators and laser energies close to 2 MJ have shown neutron yields in excess of 50 kJ. Improving on this performance requires understanding of the different degradation mechanisms. For many NIF implosions, nuclear diagnostic signatures have inferred residual hot-spot velocities that correlate with fuel areal density variations consistent with a low-order mode-1 asymmetry. A current working hypothesis attributes these asymmetries to a combination of beam to beam variations in the laser delivery and possibly coupling to target features, such as the diagnostic holes needed for x-ray imaging. Recently, a new source has been identified, thickness variation in the ablator shell. To gain better understanding and eventually mitigate the causes of < ρ R > asymmetries, 3D integrated simulations using the actual delivered laser powers are needed. To capture the effect of the diagnostic holes (DHs) using direct numerical simulation would require significantly large computational resources. Instead, our 3D simulations make use of a subgrid model developed using highly-resolved 2D simulations that include several details of the DH engineering complexity. Simulations of NIF shots using hohlraums without DHs, to isolate the effect of beam-to-beam variations, reproduce fairly well the observed nuclear diagnostic signatures. Similarly, reasonable agreement between data and simulations is also obtained in the presence of diagnostic holes. To account for the remaining discrepancies a sensitivity study of ablator thickness variation showed that 1% thickness asymmetries are comparable in effect to 1% peak drive mode-1 asymmetries. Additionally, this study identified sensitivity to variations in the imbedded doped layer (needed to shield the DT ice from the high energy x-rays generated in the hohlraum) thickness even when the inner and outer surface of the ablator are perfectly spherical.

Focusing effect of laser-driven positron jets by self-generated target sheath fields has been observed for the first time experimentally and the results are supported by the computational studies. In the experiment, OMEGA EP short-pulse (0.7 ps, 500 J) irradiates mm-size gold targets with a concave back surface and reference flat-surface targets. Both targets exhibited positrons with quasi-monoenergetic energy peaks while targets with concave curvature also showed increased number of positrons at the detector. The data is consistent with hybrid-PIC simulations confirming that the time-varying electric fields driven by electrons escaping from the target significantly change the trajectories of positrons. These simulations show a small radius of curvature on the rear side increases the relative focusing effect and the positrons to electrons ratio in the escaping plasma. For the smallest radius of curvature, positron jets that are up to 10 times denser can be achieved.

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.

This paper analyzes x-ray-driven implosions that are designed to be less sensitive to 2D and 3D effects in Hohlraum and capsule physics. Key performance metrics including the burn-averaged ion temperature, hot-spot areal density, and fusion yield are found to agree with simulations where the design adiabat (internal pressure) is multiplied by a factor of 1.4. These results motivate the development of a simple model for interpreting experimental data, which is then used to quantify how improvements in compression could help achieve ignition.

Progress in inertial confinement fusion depends on the accurate interpretation of experiments that are complex and difficult to explain with simulations. Results could depend on small changes in the laser pulse or target or physics that are not fully understood or characterized. In this paper, we discuss an x-ray-driven platform [Baker et al., Phys. Rev. Lett. 121, 135001 (2018)] with fewer sources of degradation and find the fusion yield can be described as a physically motivated function of laser energy, target scale, and implosion symmetry. This platform and analysis could enable a more experimental approach to the study and optimization of implosion physics.

A pixelated scintillator has been designed, fabricated, and tested using a laser-accelerated proton source for use in proton diagnostics at rep-rated laser facilities. The work presented here demonstrates the enhanced spatial resolution of thin, organic scintillators through a novel pixelation technique. Experimental measurements using laser-generated protons incident onto 130 μm-thick scintillators indicate a >20% reduction in the scintillator point spread function (PSF) for the detectors tested. The best performing pixelated detector reduced the ∼200 μm PSF of the stock material to ∼150 μm. The fabrication technique may be tailored to reduce the pixel size and achieve higher spatial resolutions.

We describe the overall performance of the major indirect-drive inertial confinement fusion campaigns executed at the National Ignition Facility. With respect to the proximity to ignition, we can describe the performance of current experiments both in terms of no-burn ignition metrics (metrics based on the hydrodynamic performance of targets in the absence of alpha-particle heating) and in terms of the thermodynamic properties of the hotspot and dense fuel at stagnation—in particular, the hotspot pressure, temperature, and areal density. We describe a simple 1D isobaric model to derive these quantities from experimental observables and examine where current experiments lie with respect to the conditions required for ignition.

We are reporting on a series of indirect-drive 0.9-scale CH capsule implosions (inner radius = 840 μm) fielded in low gas-fill (0.6 mg/cm3) hohlraums of 6.72 mm diameter at the National Ignition Facility. Thanks to the 11%-reduction of the capsule size at a given hohlraum diameter compared to previously tested full-scale capsules, we achieved good hot spot symmetry control near 33% cone-fraction and without the need to invoke cross beam energy transfer. As a result, we achieved a hot spot pressure of 280 ± 40 Gbar, which is the highest pressure demonstrated in layered DT implosions with CH capsules to date. Pushing this design to higher velocity resulted in a reduction of neutron yield. Highly resolved capsule simulations suggest that higher Au M-shell preheat resulted in an increase in Atwood number at the ablator–ice interface, which leads to increased fuel-ablator instability and mixing. The results reported here provide important scaling information for next-generation CH designs.

Picosecond-scale laser–matter interactions using compound parabolic concentrators have demonstrated strongly relativistic ponderomotive effects with ∼ 10 × increase in x-ray source brightness, positron production and multi-MeV proton acceleration versus flat targets, using a marginally relativistic intensity laser.

We describe two methods to analyze multiple x-ray images of a small, self-emitting object, and we apply these methods to the stagnating hotspots in inertial confinement fusion experiments. The first method, the common integrated profile, can be used to assess and quantify spatial variations in opacity. It is both a simple assessment of consistency and a sophisticated measurement of variations in a region that is otherwise difficult to observe. Second, we present a method to estimate volumes of highly asymmetric objects using multiple images of x-ray emission. The method is based on image intensities and does not require any explicit assumption of symmetry.

Experiments using the Advanced Radiographic Capability (ARC) laser at the National Ignition Facility (NIF) aim to characterize short-pulse-driven proton beams for use as both probes and drivers for high-energy-density physics experiments. Measurements of ARC-driven proton beam characteristics, such as energy spectrum and conversion efficiency, rely on the NIF Electron Positron Proton Spectrometer (NEPPS). The NEPPS diagnostic is a version of an existing particle spectrometer which is used for detecting MeV electron and positron spectra via permanent magnetic field dispersion. These spectrometers have not yet been calibrated for protons and instead use an analytical calculation to estimate the dispersion. Small variations in the field uniformity can affect the proton dispersion due to the relatively small resolving power (E/dE) for this diagnostic. A broadband energy, laser-accelerated proton source was produced at the Titan laser to experimentally calibrate the proton dispersion. These experimental data were used to test the theoretical dispersion. Numerical simulations using measurements of the magnetic field variation within the diagnostic were used to obtain a realistic proton dispersion curve for the new NEPPS units. This procedure for obtaining each independent dispersion is applicable to all EPPS and NEPPS diagnostics, given the axial magnetic field profile.

Accurate measurement of the thermal temperature in inertially confined fusion plasmas is essential for characterizing ignition performance and validating the basic physics understanding of the stagnation conditions. We present experimental results from cryogenic deuterium-tritium implosions on the National Ignition Facility using a differential filter spectrometer designed to measure the thermal electron temperature from x-ray continuum emission from the stagnated plasma. Furthermore, electron temperature measurements, used in conjunction with the Doppler-broadened DT neutron spectra, allow one to infer the partition of energy in the hot spot between internal energy and unconverted kinetic energy.

Author(s): Doeppner, T.; Swift, D.C.; Kritcher, A.L.; Bachmann, B.; Collins, G.W.; Chapman, D.A.; Hawreliak, J.; Kraus, D.; Nilsen, J.; Rothman, S.; Benedict, L.X.; Dewald, E.; Fratanduono, D.E.; Gaffney, J.A.; Glenzer, S.H.; Hamel, S.; Landen, O.L.; Lee, H.J.; LePape, S.; Ma, T.; MacDonald, M.J.; MacPhee, A.G.; Milathianaki, D.; Millot, M.; Neumayer, P.; Sterne, P.A.; Tommasini, R.; Falcone, R.W. | Abstract: We have developed an experimental platform for the National Ignition Facility that uses spherically converging shock waves for absolute equation-of-state (EOS) measurements along the principal Hugoniot. In this Letter, we present one indirect-drive implosion experiment with a polystyrene sample that employs radiographic compression measurements over a range of shock pressures reaching up to 60 Mbar (6 TPa). This significantly exceeds previously published results obtained on the Nova laser [R. Cauble et al., Phys. Rev. Lett. 80, 1248 (1998)] at a strongly improved precision, allowing us to discriminate between different EOS models. We find excellent agreement with Kohn-Sham density-functional-theory-based molecular dynamics simulations.

We present the first experimental measurement of temperature and density of a warm dense plasma produced by a pulsed power driver at the Nevada Terawatt Facility (NTF). In the early phases of discharge, most of the mass remains in the core, and it has been challenging to diagnose with traditional methods, e.g. optical probing, because of the high density and low temperature. Accurate knowledge of the transport coefficients as well as the thermodynamic state of the plasma is important to precisely test or develop theoretical models. Here, we have used spectrally resolved non-collective X-ray Thomson scattering to characterize the dense core region. We used a graphite load driven by the Zebra current generator (0.6 MA in 200 ns rise time) and the Ti He-α line produced by irradiating a Ti target with the Leopard laser (30 J, 0.8 ns) as an X-ray probing source. Using this configuration, we obtained a signal-to-noise ratio ~2.5 for the scattered signal. By fitting the experimental data with predicted spectra, we measured T = 2±1.9 eV, ρ = 0.6±0.5 gr/cc, 70 ns into the current pulse. The complexity of the dense core is revealed by the electrons in the dense core that are found to be degenerate and weakly coupled, while the ions remain highly coupled.

Understanding hydrodynamic phenomena driven by fast electron heating is important for a range of applications including fast electron collimation schemes for fast ignition and the production and study of hot, dense matter. In this work, detailed numerical simulations modelling the heating, hydrodynamic evolution, and extreme ultra-violet (XUV) emission in combination with experimental XUV images indicate shock waves of exceptional strength (200 Mbar) launched due to rapid heating of materials via a petawatt laser. We discuss in detail the production of synthetic XUV images and how they assist us in interpreting experimental XUV images captured at 256 eV using a multi-layer spherical mirror.