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.

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. As recently reported, a burning plasma state, where the alpha-heating in the plasma is the primary source of heating, was achieved in laboratory experiments. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin ``burn propagation'' into surrounding cold fuel, enabling the possibility of high energy gain. While ``scientific breakeven'' (i.e. unity target gain) has not yet been achieved, this talk reports the first controlled fusion experiment on the National Ignition Facility to produce capsule gain greater than unity (here 5.8) and reach ignition by many different formulations of the Lawson criterion. In the talk, we will discuss some key basic physics inertial confinement fusion (ICF) principles behind the burning plasma and ignition results as well as discuss future challenges.

Los Alamos “Ranchero” Magnetic Flux Compression Generators (FCGs) have been used to power imploding liner loads. The fundamental FCG design is based on a cylindrical detonation system that expands the armature simultaneously into a coaxial generator volume and has been shown to generate currents as high as 76 MA. Analysis of the 76 MA test results revealed a weakness in the design at the output glide plane. To prevent premature shorting at the output current slot of the generator, the armature/glide plane interface was originally designed to lag the leading edge of the armature. However, 2D-MHD calculations reveal that at very high currents a magnetically driven aneurism develops in this lagging section which reduces the performance of the generator. A new model Ranchero is being developed to correct this weakness and provide enhanced performance. In the new model, the output glide plane is eliminated and the armature is extended along the FCG axis, with its radius increasing along a curve until it reaches the current output slot. A cylindrical detonation system of the type required for earlier designs continues to be used, and the high explosive (HE) in the extended section is detonated by the last point of the cylindrical detonator. The stator of the FCG is contoured, allowing the contact point of the armature to zipper from the input to the output end in the last few μs of flux compression. In addition, the new model Ranchero is intended to use PBX 9501 (9501) for the HE and also remove the smoothing layer, which has been part of all Ranchero HE systems to date. Both of these factors lead to increased performance. 9501 is more energetic than the PBXN 110 used in Ranchero generators to date, and both calculations and experiments have shown that the smoothing layer is not needed when the detonator point spacing is 18 mm. Tests of original model Rancheros using PBXN 110 castable HE, with an imbedded smoothing layer, demonstrated an armature expansion velocity of 3.1 mm/μs. Further tests show that removal of the smoothing layer increases the speed to 3.3 mm/μs, and replacement of the cast PBXN 110 with 9501 without a smoother gives a velocity of 3.8 mm/μs. Designs, concerns, and experimental results facilitating the new model Ranchero are presented. In addition, performance estimates are given for the initial imploding liner tests to be conducted, and further computational details are presented in a companion paper given by C. L. Rousculp and others at this conference.

This report was prepared as an account of work sponsored by an agency of the Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product. or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer. or otherwise does not necessarily constitute or imply its endorsement, r d m mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Blast waves (BWs) form when the wave speed of an initially diffusive, supersonic radiation wave becomes subsonic and creates a radiographically-visible, hydrodynamic shock wave. BWs are a novel diagnostic in radiation-flow, code validation experiments that use Sandia's Z-accelerator's dynamic hohlraum (DH) as a radiative source. The physics models being tested are sensitive to delivered energy and power changes of better than +/- 10%; therefore, precise in-situ radiative power and energy measurements are required for quantitative comparisons between simulation and experiment. The energy sensitive BW diagnostic complements bolometric and x-ray radiometric diagnostics in providing these measurements. Recent comparisons between BW qualification experiments and simulations have revealed a spatial dependence on the radiation source. We discuss the experimental design and sensitivities for the BW diagnostic and experimental results in comparison to simulations and other diagnostics.

A Dynamic Hohlraum (DH) is formed when arrays of tungsten wires driven by a high-current pulse implode and compress a cylindrical foam target. The resulting radiation is confined by the wire plasma and forms an intense, ∼200–250eV Planckian x-ray source. The internal radiation can be used for indirect drive inertial confinement fusion. The radiation emitted from the ends can be employed for radiation flow and material interaction studies. This external radiation is accompanied by an expanding blowoff plasma. We have diagnosed this blowoff plasma using K-shell spectra of Mg tracer layers placed at the ends of some of the Dynamic Hohlraum targets. A similar diagnosis of the interior hohlraum has been carried out using Al and Mg tracers placed at 2mm depth from the ends. It is found that the blowoff plasma is about 20–25% as dense as that of the interior hohlraum, and that its presence does not significantly affect the outward flow of the nearly Planckian radiation field generated in the hohlraum interior. However, the electron temperature of the blowoff region, at ∼120eV, is only about half that of the interior hohlraum plasma.

Inertial confinement fusion at the National Ignition Facility (NIF) is a grand challenge embraced by the nation. The designs of fusion ignition targets are based primarily on the indirect drive concept in which 351 nm laser light is absorbed by the wall of a cylindrical hohlraum, typically made of Au in current experiments. The hohlraum is an energy trapping container designed to retain as much of the incident energy as possible for use inside the walls of the hohlraum. The resulting hot wall material re-radiates a large fraction of the absorbed energy in the form of an x-ray bath at a few 100 eV, which irradiates, ablates, and implodes a DT filled capsule in which fusion occurs. The efficiency with which this can be done will depend on the atomic physics of the laser-wall interaction combined with Marshak wave energy losses into the wall, laser energy reflected back out of the hohlraum due to induced laser-plasma instabilities, and x-ray energy lost out of laser entrance holes, diagnostic holes and other imperfections in the wall. Energy loss from the hohlraum may be estimated based on the area of the missing wall or simulated by 2D radiation-hydrodynamics codes such as LASNEX[1]. This experiment was an attempt to verify that the simulations done with LASNEX are accurately capturing the x-ray energy loss out of holes and other openings in the wall of a hohlraum.

Axial symmetry in x-ray radiation of wire-array z pinches is important for the creation of dynamic hohlraums used to compress inertial-confinement-fusion capsules. We present the first evidence that this symmetry is directly correlated with the magnitude of the negative radial electric field along the wire surface. This field (in turn) is inferred to control the initial energy deposition into the wire cores, as well as any current shorting to the return conductor.

The Dynamic Hohlraum (DH) radiation on the Z facility at Sandia National Laboratories is a bright source of radiant energy that has proven useful for High Energy Density (HED) physics experiments. To be useful for HED experiments, where computer simulations need to be compared with experimental measurements, the radiation output from a DH on Z needs to be well-known. We present in this paper a new method for measuring the delivered radiation energy deposited in an experiment, specifically, an experiment driven by a Z DH. This technique uses a blast wave produced in a SiO2 foam, which is initially super-sonic but transitions to sub-sonic, producing a shock at the transition point that is observable via radiography. The position of this shock is a sensitive measure of the radiation drive energy from the Z DH. Computer simulations of been used to design and analyze a Z foam blast wave experiment. This experiment has been shot on Z and experimental results compare favorably with the computations.

A dynamic Hohlraum (DH) is formed when arrays of tungsten wires driven by a high current pulse implode upon a cylindrical foam target. At impact, the wire plasma launches a radiating shock in the foam and confines the radiation. This sequence of events forms an intense, ∼200–250eV Planckian x-ray source which is a prime candidate for indirect drive inertial confinement fusion. In recent DH experiments on the 20MA Z facility, Al and MgF2 tracer layers were embedded in the cylindrical foam targets to provide K-shell lines in the keV spectral region for diagnosing the conditions of the interior Hohlraum plasma. Time-resolved K-shell spectra of both Al and Mg show mostly absorption lines. These data can be understood and quantitatively analyzed with detailed atomic and radiation transport models. The analyses show no evidence of intrinsic differences in the properties of the tops and bottoms of the Hohlraums. The interiors of the cylindrical Hohlraums are found to be hotter than the ends.

Measurements and analyses [J. P. Apruzese et al., Phys. Plasmas 12, 012705 (2005)] of Al and MgK-shell lines from tracer layers symmetrically embedded in cylindrical dynamic-Hohlraum (DH) targets, driven by two nested tungsten-wire arrays in a z pinch, suggest that the radiation temperatures near either end of top or bottom radiation exit holes (REHs) of the DHs are similar. Moreover, the measured radii inferred for the shock developed within the targets converge towards the z axis symmetrically when viewed simultaneously through either end of the Hohlraums. These two results support the earlier observation [T. W. L. Sanford et al., Phys. Plasmas 12, 022701 (2005)] that the anticorrelation of the axial power with the magnitude of tungsten-wire material flowing near (or across) the given REH is due to increased tungsten opacity at the REH. This mechanism appears to be dominant in affecting the top-bottom (anode-cathode) symmetry in axial power, rather than there being any significant up-down difference in Hohlraum temperature or shock development. Additionally, we show that the insertion of two thin annular pedestals extending into the anode-cathode gap from either electrode, just radially outside of the REHs, improves the up-down power symmetry, decreases the rise time of the axial radiation, and decreases the shot-to-shot variation in the radiation pulse shape, and shock velocity. These improvements suggest that the quality of the plasma shell, which forms within the central region of the implosion, is superior to that adjacent to either electrode. Finally, enhanced emission on axis is observed, prior to the arrival of the main mass-driven shock from the impact of the wire arrays on the target. This phenomenon is consistent with the existence of a radiation-driven shock in the foam target which calculations indicate forms from radiation generated when the outer wire-array plasma impacts the inner array of the nest.

Summary form only given. The mass of the outer and inner wire array used to drive the baseline dynamic hohlraum (DH) with pedestal target [Sanford, et al, Phys. Plasmas 13, 1 (2006)] is reversed in order to determine if the outer array is operating in a hydrodynamic- or transparent-like mode [Chittenden, et al, Phys. Plasmas 8, 675 (2001)] when the outer array impacts the inner. In contrast to the baseline, mass reversal allows the radiation measured to distinguish between the modes. For the reversed mass DH, all parameters such as wire number, array radii and target remained the same, except the diameters of the individual wires were adjusted to reverse the array mass. The measurements show unambiguously that the reversed-mass DH operates in a transparent-like mode, with the baseline consistent with transparency. Numerical simulations in the r-o plane suggest that the underlying physics of the outer array collision with the inner between the two DHs (baseline and reversed-mass) remains similar, implying that the baseline also operates with transparency. Inflection in the rate of change in the current-change is measured 4-7 ns after the radiation signal associated with the outer-inner array collision is detected, indicating that the rear portion of the resulting plasma shell of the outer array carries the current prior to the collision. Detailed analytical modeling of this current (as the outer array passes through the inner) together with numerical simulations describes probable dynamics of the current switching from outer to inner array

In recent dynamic hohlraum experiments on the Z facility, Al and MgF2 tracer layers were embedded in cylindrical CH2 foam targets to provide K-shell lines in the keV spectral region for diagnosing the conditions of the interior hohlraum plasma. The position of the tracers was varied: sometimes they were placed 2 mm from the ends of the foam cylinder and sometimes at the ends of the cylinder. Also varied was the composition of the tracers in the sense that pure Al layers, pure MgF2 layers, or mixtures of the elements were employed on various shots. Time-resolved K-shell spectra of both Al and Mg show mostly absorption lines. These data can be analyzed with detailed configuration atomic models of carbon, aluminum, and magnesium in which spectra are calculated by solving the radiation transport equation for as many as 4100 frequencies. We report results from shot Z1022 to illustrate the basic radiation physics and the capabilities as well as limitations of this diagnostic method. (C) 2005 American Institute of Physics.

Summary form only given. Critical parameters required to perform a radiation-flow experiment on a Z-pinch are the drive radiation spectrum, intensity, and time history. With the advent of the dynamic hohlraum source at the Sandia National Laboratories Z-machine the diagnostic access to monitor the drive radiation was limited to one end of a cylindrical source. Initial comparisons showed large asymmetries in intensity and time history between the two ends of a cylindrical TPX foam implosion target. Spectral analysis showed tungsten from the imploding wire array was blocking the radiation exit hole (REH) on the cathode end of the pinch. A 3 mm tall pedestal placed on the cathode end of the TPX cylinder has restored the time and intensity profile to match the output from the anode end REH. Profiles measured from some 30 shots are presented which illustrate the evolution of the diagnostic technique into a reliable power monitoring method. We have installed computer software at the Z-machine which allows spectral deconvolution and power calculations to be performed within 30 minutes after firing the machine. This rapid data analysis identifies diagnostic problems and allows adjustments to be made in experiment parameters for the following day's shot. We also present initial results from a small, 1 mm diameter, hole placed in the coupling funnel that connects the anode side REH with a radiation flow experiment. Expectations of correlating the reliable cathode end 4 mm diameter REH measurement with the small anode end REH monitor hole have proven to be both encouraging and frustrating