Fusion Ignition Research Articles

Towards p-11B medium configurations with high Pfus/PBrems ratios

Aneutronic p-11B nuclear fusion is promising for clean energy production, as it produces three (3) alpha particles with 8.7 MeV total energy. However, the main difficulty for p-11B fusion ignition (Q = Pfus/PBrems≥ 1) concerns the nuclear cross section and thus, reactivity efficiency at higher than 200 keV medium temperatures. To overcome this difficulty, the present work emphasizes on the numerical investigation of medium schemes (configurations) with enhanced reactivity. The configurations refer to the addition of energetic protons in a low-density 11boron or proton–11boron medium (n = 1020 m−3), with (np/nB) > 1 for Bremsstrahlung losses optimization and initial temperature in the range of 1 keV ≤ Tin≤ 400 keV. A self-consistent multi-fluid global particle and energy balance code, including collisions between all medium species (p, 11B, e, α), is used for the description of the temporal evolution of all fusion medium physical parameters and the evaluation of the optimum initial conditions for the obtainment of Q ≥ 1. The numerical simulation results show that the coupling between the 200 keV < Ep,0≤ 750 keV energetic protons and the 1 keV ≤ Tin≤ 400 keV initial fusion medium leads to ignition, 1 ≤ Q < 1.4, below Tin= 100 keV. In all the presented initial medium temperature cases, and especially, the lower (<) than 100 keV, the ignition condition (Pfus/PBrems) > 1 arises, as a consequence of the chain reactions and the related avalanche alpha heating effect.

Enhancing the Energy Release Performance of Al/CuO Nanothermites through Hierarchical Structure

ABSTRACT The objective of this study is to enhance the mixing uniformity and contact efficiency between nano-Al and oxidizers through structural control, while suppressing the “pre – ignition fusion” effect of nanothermites. We employed biotemplate approach, utilizing Lycopodium japonicum Thunb. spores (LP) and Papilio maackii wings (PW) as sacrificial templates, to successfully fabricate hierarchically structured Al/PW-CuO and Al/LP-CuO nanothermites. At a stoichiometric ratio of Ф = 1.5, Al/PW-CuO exhibited the highest heat release of 2278.00 J/g, whereas Al/LP-CuO also achieved a substantial heat release of 1969.08 J/g. These outstanding performances are attributed to the unique structures of PW-CuO and LP-CuO, especially the spine-like plate structure of PW-CuO, which provides more reaction sites, thereby enhancing spatial utilization and heat release efficiency. This study provides new insights for the design and application of highly active nanoenergetic materials.

The entanglement of fusion energy research and bombs

ABSTRACT The recent achievement of fusion ignition—meaning more energy came out of a self-sustaining fusion reaction than was put in—at Lawrence Livermore National Laboratory’s National Ignition Facility has brought to the fore long-simmering questions about whether certain experiments violate the Comprehensive Test Ban Treaty on nuclear explosions. Fusion research for peaceful use and military use are highly intertwined, despite attempts to cloak nuclear weapons with the aura of the so-called “peaceful atom.” Ignition has been achieved, but there is still a remarkable silence around whether pure fusion weapons—weapons that could kill large numbers of humans with neutron radiation but have blast effects much smaller than current thermonuclear weapons—are an objective of the overall program. Even if not an explicit objective, would they be built if fusion technology makes them feasible?

Simulating Nonlinear Radiation Diffusion Through Quantum Computing

The recent success of the fusion ignition experiment at Lawrence-Livermore National Laboratory has renewed excitement for inertial confinement fusion. Designing such experiments relies on computational modeling using radiation hydrodynamic codes run on massively parallel supercomputers which simulate hydrodynamic flows, radiation diffusion, and thermonuclear burn. Constructing a quantum algorithm for radiation hydrodynamics that provides a quantum speedup is of great interest. A recent quantum algorithm that solves the Navier-Stokes equations of hydrodynamics with a quadratic speedup marks a first step towards this goal. Here we take the next step and present a quantum algorithm for nonlinear radiation diffusion that also has a quadratic speedup. To verify the algorithm we consider radiation striking a cold, optically thick target that generates a Marshak wave in the target. Results of numerical simulation of the quantum algorithm are compared with those of a standard partial differential equation solver and excellent agreement is found.

Evolution of low-mode asymmetries introduced by x-ray P2 drive asymmetry during double shell implosions on the SG facility

Abstract Double shell capsule can provide a potential low-convergence to fusion ignition at relatively low temperature (∼3 keV). One of the main sources of degrading double shell implosion performance is the low-mode asymmetries. Recently, the experiments on the evolution of low-mode asymmetries introduced by x-ray P2 drive asymmetry during double shell implosions were carried out on the SG facility, where the outer shell and inner shell shapes were measured through the backlit radiography, and the fuel shape near stagnation was measured by core x-ray self-emission imaging. The time-dependent x-ray flux symmetry was controlled by varying the inner cone fraction, defined as the ratio of the inner cone power to the total laser power, while keeping the drive temperature histories same across experiments. Both the hohlraum radiation and the capsule implosions were analyzed using a two-dimensional radiation-hydrodynamics code. Comparing the experimental radiographs and self-emission images to the simulations, it is found that the simulated outer shell, inner shell and hot spot shapes are in qualitative agreement with experiments, especially, the symmetry swings of the hot spot shape near stagnation are observed from both experimental and simulation results. Further, the effect of x-ray drive asymmetries on double shell implosion performance is preliminarily investigated using numerical simulations. We find that the azimuthal variations in radial velocity caused by drive asymmetries can generate azimuthal mass flow of the inner shell, thus kinetic energy of the inner shell would be not converted into fuel internal energy with high efficiency, and the mass-averaged ion temperature of the fuel at stagnation would be reduced.

The untold history behind fusion ignition

Personal anecdotes and technical details enliven the full story of the decades-long effort that lead to the first demonstration of fusion ignition.

How ignition and target gain [formula omitted] were achieved in inertial fusion

For many decades the running joke in fusion research has been that “fusion” is twenty years away and always will be. Yet, in 2023 we find ourselves in a position where we can talk about the milestones of burning plasmas, fusion ignition, and target energy gain greater than unity in the past tense – a situation that is remarkable! This paper tells some of the story of the applied physics challenges that needed to be overcome to achieve these milestones and the strategy our team followed. Things did not always go well and some practical lessons learned are part of this story. The data shows, getting to a burning plasma in late 2020 and early 2021 was a key tipping-point, after which ignition (August 8, 2021) and target gain (December 5, 2022) were rapidly achieved.

Ionization by XFEL radiation produces distinct structure in liquid water

In the warm dense matter (WDM) regime, where condensed, gas, and plasma phases coexist, matter frequently exhibits unusual properties that cannot be described by contemporary theory. Experiments reporting phenomena in WDM are therefore of interest to advance our physical understanding of this regime, which is found in dwarf stars, giant planets, and fusion ignition experiments. Using 7.1 keV X-ray free electron laser radiation (nominally 5×105 J/cm2), we produced and probed transient WDM in liquid water. Wide-angle X-ray scattering (WAXS) from the probe reveals a new ~9 Å structure that forms within 75 fs. By 100 fs, the WAXS peak corresponding to this new structure is of comparable magnitude to the ambient water peak, which is attenuated. Simulations suggest that the experiment probes a superposition of two regimes. In the first, fluences expected at the focus severely ionize the water, which becomes effectively transparent to the probe. In the second, out-of-focus pump radiation produces O1+ and O2+ ions, which rearrange due to Coulombic repulsion over 10 s of fs. Our simulations account for a decrease in ambient water signal and an increase in low-angle X-ray scattering but not the experimentally observed 9 Å feature, presenting a new challenge for theory.

Electron-proton relaxation in hot-dense plasmas with a screened quantum statistical potential.

Modeling the nonequilibrium process between ions and electrons is of great importance in laboratory fusion ignition, laser-plasma interaction, and astrophysics. For hot and dense plasmas, theoretical descriptions of Coulomb collisions remain complicated due to quantum effect at short distances and screening effect at long distances. In this paper, we propose an analytical screened quantum statistical potential that takes into account both the short-range quantum diffraction effect and the long-range screening effect. By implementing the newly developed potential into the binary scattering framework, the electron-proton temperature relaxation in hot-dense hydrogen plasmas is investigated. In both the classical and quantum limits, analytical expressions for the Coulomb logarithm have been obtained, which are generally embedded in an asymptotic matching formula. Quantitative comparisons with molecular dynamics simulations and recent OMEGA experiments demonstrate that the present modeling is well suited to describe the temperature relaxation process between electrons and ions in hot-dense plasmas.

On the ignition of H11B fusion fuel

We have revisited recent results on the ideal ignition of H11B fuel, in the light of the latest available reactivity, an alternative self-consistent calculation of the electron temperature, an increased extent of the suprathermal effects and the impact of plasma density. At high density, we find that the ideal ignition temperature is appreciably relaxed (e.g., Ti≃150 keV for ni∼1026 cm−3 and an optimal 11B/H concentration ε=0.15) and burn becomes substantial. We have then investigated central hot-spot ignition in both isobaric and isochoric inertial confinement configurations. Although implosion-driven ignition appears to be unfeasible, the isochoric self-heating conditions foster favourable preliminary conclusions on the utilization of proton fast ignition. In the isochoric case, we find a broad minimum in the ignition energy at ρR≃8.5 g/cm2 and 220≲Ti≲340 keV (80 ≲Te≲95 keV), for ε=0.15.

Comment on “ENN's roadmap for proton-boron fusion based on spherical torus” [Phys. Plasmas 31, 062507 (2024)

This comment discusses the feasibility of hot ion mode Ti/Te=4 for proton–boron fusion, which is critical for the roadmap proposed in Liu et al. [Phys. Plasmas 31, 062507 (2024)]. The hot ion mode Ti/Te=4 has been calculated to be far from accessible (Ti/Te<1.5 for Ti=150 keV) under the most optimal conditions if fusion provides the heating [Xie, Introduction to Fusion Ignition Principles: Zeroth Order Factors of Fusion Energy Research (USTC Press, Hefei, 2023)], i.e., that all fusion power serves to heat the ions and that electrons acquire energy only through interactions with ions. We also discuss if hot ion mode of Ti/Te=4 could be achieved by an ideal heating method, which is much more efficient than fusion itself (near 20 times fusion power for Ti=150 keV) and only heats the ions, whether it makes sense economically.

Delivering laser performance conditions to enable fusion ignition, and beyond at the National Ignition Facility

On December 5th, 2022, controlled fusion ignition was demonstrated for the first time at the National Ignition Facility (NIF), a major achievement in the field of Inertial Confinement Fusion (ICF) requiring a multi-decadal effort involving broad national and international collaborations. To drive the fusion ignition reaction with the compressed fuel capsule, that yielded 3.15 MJ of nuclear energy [1], the NIF laser delivered a high-precision pulse shape with 2.05 MJ of ultra-violet (UV) laser energy and a peak power of 440 TW. This laser energy was an increase of ∼8 % compared to that delivered on the previous “threshold of ignition” record yield experiment (1.37 MJ of yield for 1.89 MJ of laser energy) on August 8th, 2021 [2].We explain how the results of our extensive research in laser technology and UV optics damage mitigation led to major improvements in the NIF laser, enabling this energy increase along with additional accuracy, precision, and power balance enhancements. Furthermore, we will discuss on-going efforts that have enabled operations at 2.2 MJ of UV energy as well as potential new initiatives to push the laser performance –accuracy and delivered energy– to even higher levels in the future as previously demonstrated on a small subset of NIF beams [3].

Design of first experiment to achieve fusion target gain > 1

A decades-long quest to achieve fusion energy target gain and ignition in a controlled laboratory experiment, dating back to 1962, has been realized at the National Ignition Facility (NIF) on December 5, 2022 [Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)] where an imploded pellet of deuterium and tritium (DT) fuel generated more fusion energy (3.15 MJ) than laser energy incident on the target (2.05 MJ). In these experiments, laser beams incident on the inside of a cylindrical can (Hohlraum) generate an intense ∼3 × 106 million degree x-ray radiation bath that is used to spherically implode ∼2 mm diameter pellets containing frozen deuterium and tritium. The maximum fusion energy produced in this configuration to date is 3.88 MJ using 2.05 MJ of incident laser energy and 5.2 MJ using 2.2 MJ of incident laser energy, producing a new record target gain of ∼2.4×. This paper describes the physics (target and laser) design of this platform and follow-on experiments that show increased performance. We show robust megajoule fusion energy output using this design as well as explore design modification using radiation hydrodynamic simulations benchmarked against experimental data, which can further improve the performance of this platform.

The electronic and optical properties of Al interstitial defects in KH2PO4 crystal: First principles study

KH2PO4 (KDP) crystals are widely used as frequency multipliers in inertial confinement controlled fusion ignition devices. The electronic and optical properties of KDP crystals with Al interstitial defects based on first principles are investigated. The results show that neutral and +3 charged Al interstitial can exist stably in the crystal. The +3 charged defect produces a larger lattice distortion. Bond length varies from −18.78 % to 43.71 % in the paraelectric phase(P-KDP) and from −25.57 % to 66.09 % in the ferroelectric phase (F-KDP). At the same time, +3 charged Al interstitial may also cause HO bond to break, resulting in the generation of H interstitials, which may compensate for the H vacancies in as-grown KDP. This may make the laser damage threshold slightly increase when KDP crystal is doped with +3 charged Al ion at low concentration. The optical spectra of Al interstitial are calculated, and the results show that in the paraelectric and ferroelectric phases, the optical transition of Al ions generally produces a large lattice relaxation energy, such as the lattice relaxation energy of up to 4.00 eV in the +2 to +3 charged defect transition in the paraelectric phase. This shows that the optical transition of Al interstitial will cause serious damage to the crystal. In the paraelectric phase, the absorption peaks of optical transitions found in the ultraviolet and visible regions are consistent with experiments. The absorption peak of the +1 to +2 charged defect transition is at 260 nm, which is very close to the absorption peak at 270 nm measured by experiments. The analysis of the Huang-Rys factors and transition displacement further confirms the conclusion that the optical transition of the defect charged state will cause serious crystal damage.

Hybrid simulation of shock interaction with highly nonuniform plasmas

The impact of capsule imperfections is one of the challenges in achieving reproducible, high-gain ignition of inertial confinement fusion (ICF). The nonuniformities of capsule imperfections, which create instability seeds during the shock propagation, may cause significant performance degradation. A systematic study of the propagation of collisional shock wave in highly nonuniform plasmas is carried out using a hybrid fluid-PIC code, which enables the analysis of electromagnetic fields, ion mixing, and plasma viscosity self-consistently. During shock propagation, it interacts with multiple bubbles and significant material mixing in the nonuniform plasmas are observed. Consequently, the average viscosity of the post-shock plasma in the nonuniform case increases to 1∼2 times that of the uniform case. These results provide a better understanding of the possible influence of capsule imperfections in ICF implosions.

A Review of Lawson Criterion for Nuclear Fusion

In the pursuit for abundant clean energy from nuclear fusion, the Lawson Criterion is cited by fusion researchers and experimentalists as the condition to exceed for fusion of atomic nuclei to occur. In his 1955 paper J.D. Lawson analyzed a fusion plasma conforming to thermodynamic principles at steadystate but with stated omissions and simplifications. Modern fusion researchers developed many incantations of the Lawson Criterion urging their brand leads to fusion ignition, necessarily to sell a rational fusion hypothesis and attract research funding. Others have shown how confined fusion in the laboratory cannot satisfy a positive energy balance due to energy losses from the system. A literature search for "fusion energy balance" shows a suspicious absence of this sanity-check to verify the energy condition was met. This paper applies conservation of energy from classical thermodynamics to a fusion plasma and summarizes eleven modern Lawson-like interpretations in a uniform way, doing so shows the requirements for fusion ignition are not met. Indeed despite billions of speculative dollars spent, sustained laboratory fusion has not been demonstrated in any experimental apparatus built and tested to date worldwide. Heed the warning, in 1955 John D. Lawson wrote: “To conclude we emphasize that these conditions, though necessary are far from sufficient. The working cycle that has been assumed is very optimistic.”

Comparison of the evolution of Rayleigh–Taylor instability during the coasting phase of the central ignition and the double-cone ignition schemes

The Rayleigh–Taylor (RT) instability has been a great challenge for robust fusion ignition. In this paper, the evolution of the RT instability at the fuel inner interface during the coasting phase is investigated for the central ignition scheme [Hurricane et al., Rev Mod Phys. 95, 025005 (2023)] and the double-cone ignition (DCI) scheme [Zhang et al., Philos. Trans. R. Soc. A. 378, 20200015 (2020)]. It is found that the spherical convergent effect can be helpful for smoothing the disturbance by merging the spikes in the azimuthal direction. For the DCI scheme, the pressure gradient in the same direction with the density gradient at the fuel inner interface can further prevent the disturbance from growing. For the example case with an initial disturbance amplitude as large as 20 μm, the DCI scheme can still reach a high-density isochoric plasma with an areal density of 2.18 g/cm2 at the stagnation moment, providing favorable conditions for fast ignition by the relativistic electron beam.

Point design of octahedral spherical Hohlraum with HDC–CH capsule for a predictable inertial confinement fusion at/beyond ignition

Fusion ignition has been successfully achieved at the National Ignition Facility, but the main obstacles of low-mode asymmetries, laser-plasma instabilities (LPIs), and hydrodynamic instabilities (HIs) still remain in the path toward a predictable yield for fusion ignition, especially at high gain. A recently proposed octahedral spherical Hohlraum, i.e., a spherical Hohlraum with six laser entrance holes of octahedral symmetry [Lan et al., Phys. Plasmas 21, 010704 (2014); Phys. Rev. Lett. 127, 245001 (2021)], was demonstrated to have the advantages of a naturally high radiation symmetry without any symmetry tuning technology and a high energy coupling efficiency from the drive laser to the capsule hotspot. In addition, a novel HDC–CH (here, HDC and CH refer to high density carbon and glow discharge plastic, respectively) capsule design was proposed to have the advantages in both low LPIs and low HIs by using two different ablators [Qiao and Lan, Phys. Rev. Lett. 126, 185001 (2021)]. For the first time, here we proposed a point design target composed of an octahedral spherical Hohlraum and an HDC–CH capsule to suppress the above-mentioned obstacles and presented the 2D simulation of the effect of symmetry and hydrodynamic instabilities on implosion performances. Our work provides a novel target design for a more predictable fusion ignition in experiment.

Diagnosing the origin and impact of low-mode asymmetries in ignition experiments at the National Ignition Facility.

Inertial confinement fusion ignition requires high inflight shell velocity, good energy coupling between the hotspot and shell, and high areal density at peak compression. Three-dimensional asymmetries caused by imperfections in the drive symmetry or target can grow and damage the coupling and confinement. Recent high-yield experiments have shown that low-mode asymmetries are a key degradation mechanism and contribute to variability. We show the experimental signatures and impacts of asymmetry change with increasing implosion yield given the same initial cause. This letter has implications for improving robustness to a key degradation in ignition experiments.

Measurements of improved stability to achieve higher fuel compression in ICF

While nuclear fusion ignition has been achieved at the National Ignition Facility in inertial confinement fusion (ICF) experiments, obtaining higher gain and more efficient burn is still desired. In that regard, increasing the compression of the fuel is an important factor. In recent indirect-drive capsule implosions, the SQ-n campaign is testing the hypothesis that reducing the hydrodynamic growth of perturbations is key to achieving higher compression of high-density carbon based-ablators for ICF. SQ-n uses a design at lower adiabat with a ramped foot laser pulse shape to minimize early-time hydrodynamic instability growth, predicted to be reduced by a factor of 10, and an optimized ablator dopant distribution. Subsets of experiments were conducted within the SQ-n campaign to study the implosion symmetry, laser backscatter, stability, and compression. Only the latter two will be reviewed here. Shock timing experiments using the velocity interferometer system for any reflector diagnostic enabled the development of a gently accelerating shock velocity. The ice–ablator interface acceleration, important for managing the Richtmyer–Meshkov phase growth, was observed with refraction enhanced radiography and the ablation front growth was measured using radiography of pre-imposed modulations. Finally, layered tritium-hydrogen-deuterium (∼75% H, ∼25% T, ∼2–10% D) and deuterium–tritium implosions demonstrate that between 15% ± 3% and 30% ± 6% improved compression has been achieved.