Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Hohlraum Reheating from Burning NIF Implosions

As fusion experiments at the National Ignition Facility (NIF) approach and exceed breakeven, energy from the burning capsule is predicted to couple to the gold walls and reheat the hohlraum. On December 5, 2022, experiment N221204 exceeded target breakeven, historically achieving 3.15 MJ of fusion energy from 2.05 MJ of laser drive; for the first time, energy from the igniting capsule reheated the hohlraum beyond the peak laser-driven radiation temperature of 313 eV to a peak of 350 eV, in less than half a nanosecond. This reheating effect has now been unambiguously observed by the two independent Dante calorimeter systems across multiple experiments, and is shown to result from reheating of the remnant tungsten-doped ablator by the exploding core, which is heated by alpha deposition.

Progress towards a more predictive model for hohlraum radiation drive and symmetry

For several years, we have been calculating the radiation drive in laser-heated gold hohlraums using flux-limited heat transport with a limiter of 0.15, tabulated values of local thermodynamic equilibrium gold opacity, and an approximate model for not in a local thermodynamic equilibrium (NLTE) gold emissivity (DCA_2010). This model has been successful in predicting the radiation drive in vacuum hohlraums, but for gas-filled hohlraums used to drive capsule implosions, the model consistently predicts too much drive and capsule bang times earlier than measured. In this work, we introduce a new model that brings the calculated bang time into better agreement with the measured bang time. The new model employs (1) a numerical grid that is fully converged in space, energy, and time, (2) a modified approximate NLTE model that includes more physics and is in better agreement with more detailed offline emissivity models, and (3) a reduced flux limiter value of 0.03. We applied this model to gas-filled hohlraum experiments using high density carbon and plastic ablator capsules that had hohlraum He fill gas densities ranging from 0.06 to 1.6 mg/cc and hohlraum diameters of 5.75 or 6.72 mm. The new model predicts bang times to within ±100 ps for most experiments with low to intermediate fill densities (up to 0.85 mg/cc). This model predicts higher temperatures in the plasma than the old model and also predicts that at higher gas fill densities, a significant amount of inner beam laser energy escapes the hohlraum through the opposite laser entrance hole.

Publisher's Note: Development of improved radiation drive environment for high foot implosions at the National Ignition Facility [Phys. Rev. Lett. 117, 225002 (2016)]

This corrects the article DOI: 10.1103/PhysRevLett.117.225002.

Development of Improved Radiation Drive Environment for High Foot Implosions at the National Ignition Facility

Analyses of high foot implosions show that performance is limited by the radiation drive environment, i.e., the hohlraum. Reported here are significant improvements in the radiation environment, which result in an enhancement in implosion performance. Using a longer, larger case-to-capsule ratio hohlraum at lower gas fill density improves the symmetry control of a high foot implosion. Moreover, for the first time, these hohlraums produce reduced levels of hot electrons, generated by laser-plasma interactions, which are at levels comparable to near-vacuum hohlraums, and well within specifications. Further, there is a noteworthy increase in laser energy coupling to the hohlraum, and discrepancies with simulated radiation production are markedly reduced. At fixed laser energy, high foot implosions driven with this improved hohlraum have achieved a 1.4×increase in stagnation pressure, with an accompanying relative increase in fusion yield of 50% as compared to a reference experiment with the same laser energy.

Thin shell, high velocity inertial confinement fusion implosions on the national ignition facility

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.

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

By using three tunable wavelengths on different cones of laser beams on the National Ignition Facility, numerical simulations show that the energy transfer between beams can be tuned to redistribute the energy within the cones of beams most prone to backscatter instabilities. These radiative hydrodynamics and laser-plasma interaction simulations have been tested against large-scale hohlraum experiments with two tunable wavelengths and reproduce the hohlraum energetics and symmetry. Using a third wavelength provides a greater level of control of the laser energy distribution and coupling in the hohlraum, and could significantly reduce stimulated Raman scattering losses and increase the hohlraum radiation drive while maintaining a good implosion symmetry.

Demonstration of ignition radiation temperatures in indirect-drive inertial confinement fusion hohlraums

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

Observation of high soft x-ray drive in large-scale hohlraums at the National Ignition Facility

The first soft x-ray radiation flux measurements from hohlraums using both a 96 and a 192 beam configuration at the National Ignition Facility have shown high x-ray conversion efficiencies of ∼85%-90%. These experiments employed gold vacuum hohlraums, 6.4 mm long and 3.55 mm in diameter, heated with laser energies between 150-635 kJ. The hohlraums reached radiation temperatures of up to 340 eV. These hohlraums for the first time reached coronal plasma conditions sufficient for two-electron processes and coronal heat conduction to be important for determining the radiation drive.

The first measurements of soft x-ray flux from ignition scale Hohlraums at the National Ignition Facility using DANTE (invited)

The first 96 and 192 beam vacuum Hohlraum target experiments have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr as viewed by DANTE representing an ∼20 times flux increase over NOVA/Omega scale Hohlraums. The vacuum Hohlraums were irradiated with 2 ns square laser pulses with energies between 150 and 635 kJ. They produced nearly Planckian spectra with about 30±10% more flux than predicted by the preshot radiation hydrodynamic simulations. To validate these results, careful verification of all component calibrations, cable deconvolution, and software analysis routines has been conducted. In addition, a half Hohlraum experiment was conducted using a single 2 ns long axial quad with an irradiance of ∼2×10(15) W/cm(2) for comparison with NIF Early Light experiments completed in 2004. We have also completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1×10(14) W/cm(2) over 5 ns) to avoid sensitivity to modeling uncertainties for nonlocal heat conduction and nonlinear absorption mechanisms, to compare with similar intensity, 3 ns OMEGA sphere results. The 2004 and 2009 NIF half-Hohlraums agreed to 10% in flux, but more importantly, the 2006 OMEGA Au Sphere, the 2009 NIF Au sphere, and the calculated Au conversion efficiency agree to ±5% in flux, which is estimated to be the absolute calibration accuracy of the DANTEs. Hence we conclude that the 30±10% higher than expected radiation fluxes from the 96 and 192 beam vacuum Hohlraums are attributable to differences in physics of the larger Hohlraums.

Optical transmission of glass for the National Ignition Facility near backscatter imagers under x-ray exposure

In experiments at the National Ignition Facility (NIF), the near backscatter imager materials need to maintain high optical transmission while exposed to hohlraum generated x rays. Glass plates are incorporated in the design to protect the optical scattering plates from x-ray damage. Radiation environments spanning those expected on NIF have been produced at the Omega Laser Facility by symmetric laser illumination of 1 mm sized gold spheres. The time-dependent ultraviolet transmission of sample glass plates was measured. The data are interpreted with a free electron absorption model. Combined with the simulations of the hohlraum x-ray emission, this model is used to predict the transmission of the glass plates on the NIF. We predict that the plates should perform adequately up to the peak of the laser pulse.

Demonstration of the density dependence of x-ray flux in a laser-driven hohlraum

Experiments have been conducted using laser-driven cylindrical hohlraums whose walls are machined from Ta2O5 foams of 100 mg/cc and 4 g/cc densities. Measurements of the radiation temperature demonstrate that the lower density walls produce higher radiation temperatures than the high density walls. This is the first experimental demonstration of the prediction that this would occur [M. D. Rosen and J. H. Hammer, Phys. Rev. E 72, 056403 (2005)10.1103/PhysRevE.72.056403]. For high density walls, the radiation front propagates subsonically, and part of the absorbed energy is wasted by the flow kinetic energy. For the lower wall density, the front velocity is supersonic and can devote almost all of the absorbed energy to heating the wall.

Creation of hot radiation environments in laser-driven targets

A hot radiation environment, produced by maximizing laser-energy deposition into a small, high- "can," is a platform being developed for investigations of material properties under extreme conditions. In such small targets, almost doubling the laser energy results in only an incremental increase in the x-radiation flux, and almost no increase in the maximum achieved radiation temperature. That most of this additional laser energy is not deposited within the target is a direct consequence of laser-plasma interactions (LPI) outside of the target, which result in high-angle beams never entering the target late in the laser pulse. Accounting for these processes in the modeling results in quantitative agreement for the first time with experiments using very small cans. These findings have provided the scientific foundation for modifying the target geometry to mitigate the LPI and to achieve higher radiation temperatures.

Measurement of the absolute hohlraum-wall albedo under ignition foot drive conditions

We present measurements of the absolute albedos of hohlraums made from gold or from high-Z mixtures. The measurements are performed over the range of radiation temperatures (70-100 eV) expected during the foot of an indirect-drive temporally shaped ignition laser pulse, where accurate knowledge of the wall albedo (i.e., soft x-ray wall reemission) is most critical for determining capsule radiation symmetry. We find that the gold albedo agrees well with calculations using the supertransition array opacity model, potentially providing additional margin for inertial confinement fusion ignition.

Detailed measurements of a diffusive supersonic wave in a radiatively heated foam

We have made the first detailed measurements of a diffusive supersonic radiation wave in the laboratory. A 10 mg/cm(3) SiO2 foam is radiatively heated by the x-ray flux from a laser-irradiated hohlraum. The resulting radiation wave propagates axially through the optically thick foam and is measured via time-resolved x-ray imaging as it breaks out the far end. The data show that the radiation wave breaks out at the center prior to breaking out at the edges, indicating a significant curvature in the radiation front. This curvature is primarily due to energy loss into the walls surrounding the foam.

Correlations between the MMPI and the Scale for the Assessment of Positive Symptoms and the Scale for the Assessment of Negative Symptoms in schizophrenic patients

Our study examined the relationship between the Minnesota Multiphasic Personality Inventory (MMPI) and the Scale for the Assessment of Positive Symptoms (SAPS; Andreason, 1984) and the Scale for the Assessment of Negative Symptoms (SANS; Andreason, 1983) in patients who met the Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; American Psychiatric Association, 1987) diagnostic criteria for schizophrenia (n = 125). A significant correlation was found between the SAPS Delusions scale and Scale 6 (Paranoia), the SAPS Positive Thought Disorder Scale and Scale F (Infrequency), and the SAPS Positive Thought Disorder and Scale 9 (Hypomania). Additional analysis also shows, however, that severity of symptoms was the best predictor of MMPI scores. Consistent with previous studies, the MMPI appears useful for screening but not for the detailed evaluation of symptomatology of schizophrenic patients.

Plasma production from ultraviolet-transmitting targets using subpicosecond ultraviolet radiation

Plasma produced from ultraviolet-transmitting solid targets undergoing intense (>10(16) W/cm(2)) subpicosecond (~600 fs) ultraviolet (248 nm) irradiation have been studied under conditions for which no interfering prepulse plasma is generated. Time and spatially integrated measurements of the x-ray emission for H-like and He-like Mg and Si were found to be consistent with LASNEX calculations that model the laser-target interaction.

Ultrafast X-ray Pulses from Laser-Produced Plasmas

A high-temperature plasma is created when an intense laser pulse is focused onto the surface of a solid. An ultrafast pulse of x-ray radiation is emitted from such a plasma when the laser pulse length is less than a picosecond. A high-speed streak camera detector was used to determine the duration of these x-ray pulses, and computer simulations of the plasmas agree with the experimental results. Scaling laws predict that brighter and more efficient x-ray sources will be obtained by the use of more intense laser pulses. These sources can be used for time-resolved x-ray scattering studies and for the development of x-ray lasers.

Wavelength choice for soft x-ray laser holography of biological samples: errata

This Letter points out several errors made in the printing of the original submission.

Wavelength choice for soft x-ray laser holography of biological samples

The choice of an optimal wavelength for soft x-ray holography is discussed, based on a description of scattering by biological structures within an aqueous environment. We conclude that wavelengths slightly longer than the 43.7-A carbon K-edge provide a good trade off between minimizing the necessary source power and the dose absorbed by the sample and maximizing the penetrability of the x-rays through wet samples. This differs from the previous notion that wavelengths within the water window (between 23.2 A and 43.7 A) would be the best for holography. The problem of motion resulting from the absorption of x rays during a short exposure is described. The possibility of using ultrashort exposures in order to capture the image before motion can compromise the resolution is explored. The impact of these calculations on the question of the feasibility of using an x-ray laser for holography of biological structures is discussed.

Structure of the human CR1 gene. Molecular basis of the structural and quantitative polymorphisms and identification of a new CR1-like allele

Structural and quantitative polymorphisms have been described in human CR1. In the former, the S allotype is larger than the F allotype by 40-50 kD, the size of a long homologous repeat (LHR). In the latter, homozygotes for a 7.4-kb Hind III fragment express fourfold more CR1 per erythrocyte than do homozygotes for the allelic 6.9-kb restriction fragment. The basis for these genomic polymorphisms has been determined by restriction mapping the entire S allele and part of the F allele. The S allele is 158 kb and contains 5 LHRs of 20-30 kb, designated -A, -B/A, -B, -C, and -D, respectively, 5' to 3'. Extensive homology was found among the LHRs in their restriction maps, exon organization, and the coding and noncoding sequences. The presence of LHR-B/A in the S allele but not in the F allele accounts for the longer transcripts and polypeptide associated with the former allotype. At least 42 exons are present in the S allele, with distinct exons for the leader sequence, the transmembrane and cytoplasmic regions and most of the SCRs comprising the extracellular portion of CR1. Consistent with the mapping of the ligand binding site to the first two SCRs in each LHR, the second SCRs in LHR-A, -B/A, -B, and -C are encoded by two exons, reflecting a specialized function for this unit. The allelic 7.4/6.9-kb Hind III fragments extend from the 3' region of LHR-C to LHR-D. The 6.9-kb restriction fragment is the result of a new Hind III site generated by a single base change in the intron between the exons encoding the second SCR of LHR-D. A second cluster of genomic clones has been identified by hybridization to CR1 probes. Although they contain regions of hybridization to the cDNA and genomic probes derived from CR1, these cannot be overlapped with the structural gene owing to their distinct restriction maps. Three genomic polymorphisms previously identified by CR1 cDNA probes map to this region. These additional clones may represent part of a duplicated allele located nearby within the CR1 locus.

Topography of focal proximal tubular necrosis after ischemia with reflow in the rat kidney

The topography of renal injury after ischemia-reflow was studied in intact rats by clamping the right renal artery for variable periods of time and examining the histologic appearance of the kidney in large 1-mu plastic sections. As reported by others, the straight portion of the proximal tubule (S3) was especially susceptible to ischemia-reflow injury. The pattern of focal necrosis produced in S3 by short (15-30-minute) and longer (45-60-minute) periods of arterial occlusion appeared related to gradients to oxygenation during reflow, in that more extensive injury was seen in areas remote from blood vessels, while perivascular tubules were protected. A similar pattern was seen in S1 and S2 after a longer period (45-60-minutes) of ischemia, which produced extensive but incomplete necrosis in these convoluted segments, with protected tubules lying within zones surrounding arcuate and interlobular arteries. The immediate postglomerular portion of S1, a tubular segment normally well supplied with oxygen, was an exception to this rule. Selective necrosis limited to this portion of the nephron appeared after only 15-30 minutes of ischemia, recalling the special sensitivity of S1 cells to inhibition of mitochondrial respiration. These results suggest that in different segments of the proximal tubule, injury after ischemia-reflow is determined not only by changes that occur during complete ischemia but also by the adequacy of oxygenation during the reflow period.

An Aid to Stabilization of the Anesthesia Inhaler

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