Inertial Confinement Fusion Program Research Articles

A compact and portable gamma-ray spectrometer (GRASP) for inertial confinement fusion and basic science experiments.

A compact and portable gamma-ray spectrometer has been designed to diagnose different components of the inertial confinement fusion-relevant γ-ray spectrum with energies between ∼3.7-17.9MeV. The system is designed to be as compact as possible for convenient transportation and fielding in diagnostic ports on the OMEGA laser, the National Ignition Facility, and other photon-source facilities. The system consists of a conversion foil for Compton scattering in front of four magnetic spectrometer "arms," each covering a different energy range and constructed out of cylindrical permanent magnet Halbach arrays. Monte Carlo simulations have been used to optimize and assess the performance of the conversion foil, and COSY INFINITY ion-optical simulations have been used to optimize the spectrometer magnets. The performance of the design is assessed for a simulated direct-drive γ-ray spectrum. Spanning its total γ-ray energy bandwidth and using a 1.7mm thick boron conversion foil, the system's total energy resolution and efficiency are ∼15.8%-4.5% and 5.4 × 10-7-3.7 × 10-7e-/γ, respectively, with room for improvement. Spectral γ-ray measurements will provide guidance to the inertial confinement fusion program toward achieving high-energy gain relevant to inertial fusion energy and enable new measurement capabilities for basic discovery science.

How numerical simulations helped to achieve breakeven on the NIF

The inertial confinement fusion program relies upon detailed simulations with inertial confinement fusion (ICF) codes to design targets and to interpret the experimental results. These simulations treat as much physics from essential principles as is practical, including laser deposition, cross beam energy transfer, x-ray production and transport, nonlocal thermal equilibrium kinetics, thermal transport, hydrodynamic instabilities, thermonuclear burn, and transport of reaction products. Improvements in radiation hydrodynamic code capabilities and vast increases in computing power have enabled more realistic, accurate 3D simulations that treat all known asymmetry sources. We describe how numerical simulations helped to guide the program, assess the impediments to breakeven, and optimize every aspect of target design. A preshot simulation of the first National Ignition Facility experiment that surpassed breakeven predicted an increased yield that matches the experimental result, within the preshot predicted uncertainty, with a target gain of 1.5. We will cover the key developments in Lawrence Livermore National Laboratory ICF codes that enabled these simulations and give specific examples of how they helped to guide the program.

From KMS Fusion to HB11 Energy and Xcimer Energy, a personal 50 year IFE perspective

Shortly after the laser was invented in 1960, scientists sought to use it for thermonuclear fusion. By 1963, Livermore had a classified laser inertial confinement fusion (ICF) program and leaders predicted scientific breakeven by 1973. In 1974, KMS Fusion, Inc. announced thermonuclear neutrons from a laser target and promised grid electricity within 10 years. Private capital was attracted, but the data fell far short of the optimistic simulations. Magnetic fusion energy has had civilian funding (DOE), while ICF has primarily received military funding (DOE Defense Programs and now NNSA). As bigger lasers have been built and better simulations performed, optimism about ICF breakeven has waxed and waned. The achievement of ignition and gain on NIF has validated ICF's scientific basis, and the DOE and venture capital funded private companies are again interested in inertial fusion energy (IFE). The new DOE Milestone-Based Fusion Development Program is creating public–private partnerships to accelerate progress toward fusion pilot plants. ARPA-E, DOE INFUSE, and DOE IFE STAR are also building a U.S. IFE program within DOE. The U.S. leads in ICF, but developing IFE is an international competition. Private companies are leading the way. HB11 Energy Pty Ltd. is pursuing the aneutronic proton–boron fuel cycle. Xcimer Energy is developing a disruptive IFE technology to achieve high laser energies at dramatically lower costs. This 50-year perspective discusses where the U.S. IFE program is headed and promising strategies for progress in establishing an effective U.S. IFE program from both public and private perspectives.

Development of Stochastic Voronoi Lattice Structures via Two-Photon Polymerization

ABSRACT Low-density polymer foams of varying sizes, shapes, and densities are of specific interest to the inertial confinement fusion (ICF) program and related high-energy density plasma physics research. Historically, these foams are comprised of polystyrene or other low atomic number materials and have densities in the 30 to 300 mg/cm3 range. However, at the lower end of this density range, these traditional polymer foams become fragile and difficult to cast and machine into the geometries needed. Recently, the need by experimentalists for materials with densities below 30 mg/cm3 has increased. To address these needs, we are developing three-dimensional (3-D) printing techniques to create high-precision, low-density, and repeatable complex lattice structures. Using two-photon polymerization 3-D printing, we recently developed the first 5 mg/cm3 low-density lattice structure having an annular hemispherical shape. These microscale to mesoscale structures were modeled and designed using the nTopology software, specifically utilizing the “Voronoi volume lattice” and “random points in body” option blocks. All printing operations were performed using the Nanoscribe Photonic Professional GT instrument. Characterization of these 3-D structures was conducted using various microscopic and X-ray tomographic imaging techniques. Overall printed part sizes ranged from 1 to 5 mm in diameter and were composed of lattice ligaments having thicknesses in the 3- to 5-µm range. These structures have been incorporated into ICF targets recently shot on both the University of Rochester’s Laboratory of Laser Energetics Omega laser and the National Ignition Facility.

Advancing the study of hybrid-drive inertial fusion ignition and high energy density physics - Teller medal lecture at IFSA2019

The inertial confinement fusion (ICF) program toward ignition in China has made great progress since 1993. After research work on SG series with laser energy of tens kJ, SG-III laser facility with energy output of hundreds kJ is being used to study target physics prior to ignition. A new hybrid drive (HD) approach combined indirect drive (ID) and direct drive (DD) provides the HD pressure far greater than the radiation ablation pressure to drive implosion dynamics and hotspot ignition occurring in nonstagnation time when severe hotspot deformation and hydrodynamic instabilities have not fully developed. Experiments on SG-III have verified the boost effect of the HD pressure and showed lower fractions of laser backscattering and hot-electron energy. The development of the ICF program has advanced the study of high energy density physics. An energy band theory for warm dense matter has been proposed and a new code has been developed to study equation of state and transport coefficients for ICF implosion matter and the interion properties of planets.

Analysis of NIF scaling using physics informed machine learning

Over 120 DT ice layer thermonuclear (TN) ignition experiments in inertial confinement fusion (ICF) were conducted on the National Ignition Facility (NIF) in the last eight years. None of the experiments achieved ignition. In fact, the measured neutron outputs from the experiments were well below what was expected. Although experiments to fine-tune the target designs are the focus of the national ICF program, insightful analysis of the existing data is a pressing need. In highly integrated ignition experiments, it is impossible to vary only one design parameter without perturbing all the other implosion variables. Thus, to determine the nonlinear relationships between the design parameters and performance from the data, a multivariate analysis based on physics models is necessary. To this end, we apply machine learning and deep learning methods to the existing NIF experimental data to uncover the patterns and physics scaling laws in TN ignition. In this study, we focus on the scaling laws between the implosion parameters and neutron yield using different supervised learning methods. Descriptions, comparisons, and contrasts between the methods are presented. Our results show that these models are able to infer a relationship between the observed stagnation conditions and neutron yields. This exploratory study will help build new capabilities to evaluate capsule designs and provide suggestions for new designs.

Investigation of Metal Ion Diffusion and Reduction Potential in Several Ionic Liquids

Electrodeposition is proving to be a promising technique for forming metal capsules and other components required for Inertial Confinement Fusion (ICF) experiments performed at the National Ignition Facility. While we have recently demonstrated that non-porous, defect free parts can be electrodeposited from a variety of water-based solutions,1,2 many of the preferred metals for the ICF program (beryllium, uranium, etc.) cannot be deposited because electrolysis of water occurs at the potential required to reduce such metals. To circumvent this, we are currently investigating Ionic Liquids (ILs) as solvents for metal electrodeposition, as the wide (~ 6 V) electrochemical window of ILs is expected to allow electrodeposition of Be, U, and many other metals.3 We are investigating the key parameters of metal ion diffusion and reduction potential for two model metals, silver and copper, in several different ionic liquids. We use electrochemical measurements along with first principles density functional theory (DFT) simulations to understand how ionic liquids affect diffusion and reduction potential, and this understanding will be applied to selecting appropriate ILs for deposition of metals such as Be and U. Funding was provided by Lawrence Livermore National Laboratory Directed Research and Development (LDRD) Grant 17-ERD-047. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release LLNL-ABS-771850. (1) Horwood, C.; Stadermann, M.; Bunn, T. L. Fusion Sci. Technol. 2018, 73 (3). (2) Bunn, T.; Horwood, C.; Stadermann, M. Cathode System for Electrodeposition of Metals on Microspheres. US Patent 16336-000075-US-PS1, 2018. (3) Electrodeposition from ionic liquids, 2nd ed.; Endres, F., Abbott, A., MacFarlane, D., Eds.; Wiley-VCH: Weinheim, Germany, 2017.

Obstructed View Factor Calculations for Multiple Obstructions in Closed Cavities

The inertial confinement fusion (ICF) program has been mainly concentrating on the indirect drive approach for the last three decades, due to relaxed requirements on driver-beam uniformity and reduced sensitivity to hydrodynamic instabilities. The optimal designs are important for maximum conversion of driving energy to X-rays, and finally, symmetrical irradiation of the capsule. The view factor (VF) evaluation is an important parameter providing significant radiation heat transport information in specific geometries. The present study is aimed at the VF calculations for closed cavities. The VF calculations include the case of energy transfer from one infinitesimal surface element of the enclosure to other similar infinitesimal surface elements of the cavity. Similarly, the obstructed VF is also calculated when multiple obstructions are present in the cavity. Two distinct computer programs are developed by programming in FORTRAN-90 to evaluate unobstructed VF and obstructed VF for a square geometry. The calculations are based on the crossed strings method, which is more reliable for simple geometries. The shadow effect method is used for the obstructed VF calculations. The results of the developed programs are benchmarked using the summation rule. In the case of no obstacles in the cavity, VF calculations solely obey the summation rule. However, in the presence of obstacles in the cavity, obstructed VF calculations showed the acceptable difference in comparison with the summation rule.

The National Direct-Drive Inertial Confinement Fusion Program

The National Direct-Drive Inertial Confinement Fusion Program consists of the 100 Gbar Campaign on the 30 kJ, 351 nm, 60-beam OMEGA Laser System and the megajoule direct-drive (MJDD) Campaign on the 1.8 MJ, 351 nm, 192-beam National Ignition Facility (NIF). The main goals of the 100 Gbar Campaign are to demonstrate and understand the physics for hot-spot conditions and formation relevant for ignition at the MJ scale, while the MJDD Campaign seeks to understand the laser plasma interactions, energy coupling, and laser imprint for ignition-scale direct-drive coronal plasmas. An overview of the multiyear, systematic effort that is underway for the National Direct-Drive Inertial Confinement Fusion Program (including laser, target, and diagnostic improvements in progress), as well as recent results from the 100 Gbar Campaign on OMEGA and the MJDD Campaign on NIF is presented in this paper.

Hydrodynamic instability seeding by oxygen nonuniformities in glow discharge polymer inertial fusion ablators

The U.S. indirect drive inertial confinement fusion (ICF) program uses glow discharge polymer (GDP) as one of the ablator materials for the ICF experiments at the National Ignition Facility (NIF). The performance of those implosions may be adversely affected by photoactivated uptake of oxygen impurities in the surface of the GDP ablator. These impurities can induce significant perturbations in the shock waves generated in the ablator. These perturbed shocks generate mass modulations that are amplified by Rayleigh-Taylor (RT) instability and reduce the performance of the implosions. Here we report on experiments that provide a quantitative connection between photoactivated oxygen uptake in GDP samples and modulations in shock velocities in the samples. The observed shock nonuniformity confirms the hypothesis that irregular oxygenation is a competent seed for the RT and can have a significant effect on NIF GDP implosions.

A Review of Equation-of-State Models for Inertial Confinement Fusion Materials

Material equation-of-state (EOS) models, generally providing the pressure and internal energy for a given density and temperature, are required to close the equations of hydrodynamics. As a result they are an essential piece of physics used to simulate inertial confinement fusion (ICF) implosions. Historically, EOS models based on different physical/chemical pictures of matter have been developed for ICF relevant materials such as the deuterium (D2) or deuterium-tritium (DT) fuel, as well as candidate ablator materials such as polystyrene (CH), glow-discharge polymer (GDP), beryllium (Be), carbon (C), and boron carbide (B4C). The accuracy of these EOS models can directly affect the reliability of ICF target design and understanding, as shock timing and material compressibility are essentially determined by what EOS models are used in ICF simulations. Systematic comparisons of current EOS models, benchmarking with experiments, not only help us to understand what the model differences are and why they occur, but also to identify the state-of-the-art EOS models for ICF target designers to use. For this purpose, the first Equation-of-State Workshop, supported by the US Department of Energy’s ICF program, was held at the Laboratory for Laser Energetics (LLE), University of Rochester on 31 May–2nd June, 2017. This paper presents a detailed review on the findings from this workshop: (1) 5–10% model-model variations exist throughout the relevant parameter space, and can be much larger in regions where ionization and dissociation are occurring, (2) the D2 EOS is particularly uncertain, with no single model able to match the available experimental data, and this drives similar uncertainties in the CH EOS, and (3) new experimental capabilities such as Hugoniot measurements around 100 Mbar and high-quality temperature measurements are essential to reducing EOS uncertainty.

Stockpile stewardship in the light of national ignition campaign experience

ABSTRACTUncontrolled risk is inherent in any program that lacks a proven means for revealing improper system performance, and the U.S. Stockpile Stewardship Program (SSP) is no exception. The downside of uncontrolled risk has been illustrated by the outcome of the National Ignition Campaign (NIC), a part of the Inertial Confinement Fusion (ICF) Program that has long been characterized as a crucial adjunct to the U.S. nuclear weapons program. For most of its duration, the NIC utilized simulations and partial-system experiments at several facilities, adding full-system experiments at the National Ignition Facility (NIF) only at the very end of the program. Uncontrolled risk was present in the program while those experiments were absent. That risk materialized when failure to achieve fusion capsule ignition was repeatedly and conclusively demonstrated in full-system experiments. For the SSP, the corresponding risk is that expectations concerning the safety, performance, and reliability of weapons in the stockpile are significantly incorrect. The only proven way of controlling that risk—finding out whether the expectations are wrong—requires nuclear testing. In its absence, this risk is not controlled by the SSP. The ongoing presence of uncontrolled risk in the U.S. nuclear stockpile leads inevitably to uncertainty in the effectiveness of the U.S. nuclear deterrent. None of the potential consequences of that uncertainty, one of which is a decrease in the deterrent's effectiveness, are beneficial to the United States or those who rely on its nuclear umbrella.

Laser-driven magnetized liner inertial fusion on OMEGA

Magneto-inertial fusion (MIF) combines the compression of fusion fuel, a hallmark of inertial confinement fusion (ICF), with strongly magnetized plasmas that suppress electron heat losses, a hallmark of magnetic fusion. It can reduce the traditional velocity, pressure, and convergence ratio requirements of ICF. The magnetized liner inertial fusion (MagLIF) concept being studied at the Z Pulsed-Power Facility is a key target concept in the U.S. ICF Program. Laser-driven MagLIF is being developed on OMEGA to test the scaling of MagLIF over a range of absorbed energy of the order of 1 kJ on OMEGA to 500 kJ on Z. It is also valuable as a platform for studying the key physics of MIF. An energy-scaled point design has been developed for OMEGA that is roughly 10 × smaller in linear dimensions than Z MagLIF targets. A 0.6-mm-outer-diameter plastic cylinder filled with 2.4 mg/cm3 of D2 is placed in a ∼10-T axial magnetic field, generated by a Magneto-inertial fusion electrical discharge system, the cylinder is compressed by 40 OMEGA beams, and the gas fill is preheated by a single OMEGA beam propagating along the axis. Preheating to >100 eV and axially uniform compression over 0.7 mm have been demonstrated, separately, in a series of preparatory experiments that meet our initial expectations. The preliminary results from the first integrated experiments combining magnetization, compression, and preheat demonstrating a roughly 2 x increase in the neutron yield will be reported here for the first time.

The design of the optical Thomson scattering diagnostic for the National Ignition Facility.

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.

The preliminary design of the optical Thomson scattering diagnostic for the National Ignition Facility

The National Ignition Facility (NIF) is a 192 laser beam facility designed to support the Stockpile Stewardship, High Energy Density and Inertial Confinement Fusion programs. We report on the preliminary 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 beamsplitter and gratings before the shot. A deep-UV probe beam (λ0 between 185-215 nm) will optimally collect Thomson scattered light from plasma densities of 5 x 1020 electrons/cm3 while a 3ω probe will optimally collect Thomson scattered light from plasma densities of 1 x 1019 electrons/cm3. We report the phase I design of a two phase design strategy. Phase I includes the OTS recording system to measure background levels at NIF and phase II will include the integration of a probe laser.

Alternative Approaches to High Energy Density Fusion

This paper explores selected approaches to High Energy Density (HED) fusion, beginning with discussion of ignition requirements at the National Ignition Facility (NIF). The needed improvements to achieve ignition are closely tied to the ability to concentrate energy in the implosion, manifested in the stagnation pressure, Pstag. The energy that must be assembled in the imploded state to ignite varies roughly as Pstag-2, so among other requirements, there is a premium on reaching higher Pstag to achieve ignition with the available laser energy. The U.S. inertial confinement fusion program (ICF) is pursuing higher Pstag on NIF through improvements to capsule stability and symmetry. One can argue that recent experiments place an approximate upper bound on the ultimate ignition energy requirement. Scaling the implosions consistently in spatial, temporal and energy scales shows that implosions of the demonstrated quality ignite robustly at 9-15 times the current energy of NIF. While lasers are unlikely to reach that bounding energy, it appears that pulsed-power sources could plausibly do so, giving a range of paths forward for ICF depending on success in improving energy concentration. In this paper, I show the scaling arguments then discuss topics from my own involvement in HED fusion. The recent Viewfactor experiments at NIF have shed light on both the observed capsule drive deficit and errors in the detailed modelling of hohlraums. The latter could be important factors in the inability to achieve the needed symmetry and energy concentration. The paper then recounts earlier work in Fast Ignition and the uses of pulsed- power for HED and fusion applications. It concludes with a description of a method for improving pulsed-power driven hohlraums that could potentially provide a factor of 10 in energy at NIF-like drive conditions and reach the energy bound for indirect drive ICF.

The updated advancements of inertial confinement fusion program in China

The recent achievements of ICF research in China are reviewed. The constructions of laser facilities of SG-III and SG-IIUP are completed in this year and the full energy output operation will be in 2014. The target physics studies involving numerical simulations of a new ignition scheme, which is proposed to enhance implosion velocity and suppress hydrodynamic instability and distortion at interface between hot spot and main fuel, and experimental results (a few selected examples) are presented.

An easily assembled double T-shape for the preparation of submillimeter-sized hollow polyacrylonitrile (PAN) microcapsules for inertial confinement fusion (ICF) project

An off-the-shelf device combined with commercial double T-shape adapters that performs as a micro double emulsion generator was presented in this paper. The advantage of this device lies in that it is assembled very conveniently and the channel needn’t any modification to produce O/W/O double emulsion droplets. High-quality hollow PAN microcapsules were fabricated for the purpose of ICF program through the device. Density-matched three-phase solutions were confected to form stable double emulsions. Initial eccentric double emulsions were able to adjust to be concentric during the process of flowing from the tube to the collection cylinder or self-adjustment during rotary evaporation. When the parameters of three-phase solutions and the tube's diameter were fixed, sizes of the emulsions were mainly related with the flowing velocities of the three-phase solutions. Solidification parameters were optimized to gain high-quality microcapsules. Finally, inner solvent was eliminated with supercritical drying method and the solvent-free targets were obtained. The obtained high-quality hollow microcapsules will have potential application in the ICF program in the future.

Review of the phenomenon of dips in spectral lines emitted from plasmas and their applications

The review covers theoretical and experimental studies of two kinds of dips (local depressions) in spectral line profiles emitted by plasmas: Langmuir-wave-caused dips (L-dips) and charge-exchange-caused dips (X-dips). Positions of L-dips (relative to the unperturbed wavelength of a spectral line) scale with the electron density Ne roughly as Ne1/2, while positions of X-dips are almost independent of Ne. L-dips and X-dips phenomena are interesting and important both fundamentally and practically. The fundamental interest is due to a rich physics behind each of these phenomena. As for important practical applications, they are as follows. Observation of L-dips constitutes a very accurate method to measure the electron density in plasmas - the method that does not require the knowledge of the electron temperature. L-dips also allow measuring the amplitude of the electric field of Langmuir waves - the only one spectroscopic method available for this purpose. In the most recent laser plasma experiments, L-dips were found to be a spectroscopic signature of the two-plasmon decay instability. This instability causes hot-electron generation and is a critical part in laser-driven inertial confinement fusion program. As for observations of X-dips, they serve to determine rates of charge exchange between multicharged ions. This is an important reference data virtually inaccessible by other experimental methods. The rates of charge exchange are essential for magnetic fusion in tokamaks, for population inversion in the soft x-ray and VUV ranges, for ion storage devices, as well as for astrophysics (e.g., for the solar plasma and for determining the physical state of planetary nebulae).

Managing NIF Safety Equipment in a High Neutron and Gamma Radiation Environment

The National Ignition Facility (NIF) is a 192 laser beam facility that supports the Inertial Confinement Fusion program. During the ignition experimental campaign, the NIF is expected to perform shots with varying fusion yield producing 14 MeV neutrons up to 20 MJ or 7.1 × 10(18) neutrons per shot and a maximum annual yield of 1,200 MJ. Several infrastructure support systems will be exposed to varying high yield shots over the facility's 30-y life span. In response to this potential exposure, analysis and testing of several facility safety systems have been conducted. A detailed MCNP (Monte Carlo N-Particle Transport Code) model has been developed for the NIF facility, and it includes most of the major structures inside the Target Bay. The model has been used in the simulation of expected neutron and gamma fluences throughout the Target Bay. Radiation susceptible components were identified and tested to fluences greater than 10(13) (n cm(-2)) for 14 MeV neutrons and γ-ray equivalent. The testing includes component irradiation using a 60Co gamma source and accelerator-based irradiation using 4- and 14- MeV neutron sources. The subsystem implementation in the facility is based on the fluence estimates after shielding and survivability guidelines derived from the dose maps and component tests results. This paper reports on the evaluation and implementation of mitigations for several infrastructure safety support systems, including video, oxygen monitoring, pressure monitors, water sensing systems, and access control interfaces found at the NIF.