Field Of Inertial Confinement Fusion Research Articles

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].

Anisotropic evolutions of the magnetohydrodynamic Richtmyer-Meshkov instability induced by a converging shock.

The investigation of the converging shock-induced Richtmyer-Meshkov instability, which arises from the interaction of converging shocks with the interface between materials of differing densities in cylindrical capsules, is of significant importance in the field of inertial confinement fusion (ICF). The use of converging shocks, which exhibit higher efficiency than planar shocks in the development of the RMI due to the Bell-Plesset effects, is particularly relevant to energy production in the ICF. Moreover, external magnetic fields are often utilized to mitigate the development of the RMI. This paper presents a systematic investigation of the anisotropic nature of the Richtmyer-Meshkov instability in magnetohydrodynamic induced by the interaction between converging shocks and perturbed semicylindrical density interfaces (DI) based on numerical simulations using Athena++. The results reveal that magnetic fields with β=1000, 100, and 10 (β is defined as the ratio of the plasma pressure to the magnetic pressure) lead to an anisotropic intensification of magnetic fields, anisotropic accelerations of various shock waves [including the converging incident shock (CIS), transmitted shock (TS), and reflected shock (RS)], and anisotropic growth of the DI with subsequent anisotropic vorticity distribution. Upon closer inspection, it becomes evident that these phenomena are strongly interconnected. In particular, the region where the wave front of the CIS impacts the middle point of semicylindrical DI, where the magnetic field is more perpendicular to the fluid motion, experiences a more significant amplification of the magnetic fields. This generates higher-pressure jumps, which in turn accelerates the shock wave near this region. Furthermore, the anisotropic amplification of the magnetic fields reduces the movement of the RMI near the middle point of semicylindrical DI and leads to the anisotropic formation of RMI-induced bubbles and spikes, as well as vortices. By examining vorticity distributions, the results underscore the crucial role of magnetic tension forces in inhibiting fluid rotation.

Research on Laser-Induced Damage Post-Restoration Morphology of Fused Silica and Optimization of Patterned CO2 Laser Repair Strategy.

Fused silica has become the preferred optical material in the field of inertial confinement fusion (ICF) due to its excellent performance; however, these costly optical elements are vulnerable, and their manufacture is time-consuming. Therefore, the restoration of laser-induced damage for these optical elements is of great value. To restrain the post-restoration raised rim problem in the CO2 laser repair process to improve the restoration quality, the separate influences of key parameters of laser power, irradiation duration, and laser beam diameter on post-restoration pit morphology are compared in combined simulation and experimental studies. An optimized, patterned CO2 laser strategy is proposed and verified; the results indicate that, with the strategy, the rim height decreases from 2.6 μm to 1.52 μm, and maximal photo thermal absorption is decreased from 784.2 PPM to 209.43 PPM.

Estimation of the FST-Layering Time for Shock Ignition ICF Targets

The challenge in the field of inertial confinement fusion (ICF) research is related to the study of alternative schemes for fuel ignition on laser systems of medium and megajoule scales. At the moment, it is considered promising to use the method of shock ignition of fuel in a pre-compressed cryogenic target using a focused shock wave (shock- or self-ignition (SI) mode). To confirm the applicability of this scheme to ICF, it is necessary to develop technologies for mass-fabrication of the corresponding targets with a spherically symmetric cryogenic layer (hereinafter referred to as SI-targets). These targets have a low initial aspect ratio Acl (Acl = 3 and Acl = 5) because they are expected to be more hydrodynamically stable during implosion. The paper discusses the preparation of SI-targets for laser experiments using the free-standing target (FST) layering method developed at the Lebedev Physical Institute (LPI). It is shown that, based on FST, it is possible to build a prototype layering module for in-line production of free-standing SI-targets, and the layering time, τform, does not exceed 30 s both for deuterium and deuterium-tritium fuel. Very short values of τform make it possible to obtain layers with a stable isotropic fuel structure to meet the requirements of implosion physics.

Equations of state of poly- α -methylstyrene and polystyrene: First-principles calculations versus precision measurements

We show with a recently devised extended first-principles molecular dynamics method that calculated Hugoniots of poly-$\ensuremath{\alpha}$-methylstyrene agree well with precision experimental results of Kritcher et al. [Nature (London) 584, 51 (2020)] and D\oppner et al. [Phys. Rev. Lett. 121, 025001 (2018)]. The deviation is smaller than 0.8%. This agreement does not sensitively rely on the approximations in the employed first-principles methods as long as underlying physics are well described, as illustrated in the calculation of equation of state for polystyrene covering the warm dense regime. These results may stimulate a broad range of quantitative investigations on warm dense matter that were not thought possible before, and may thus afford a new prospect to the field of inertial confinement fusion and high-energy-density physics.

Study of the asymmetry of hot-spot self-emission imaging of inertial confinement fusion implosion driven by high-power laser facilities

Implosion asymmetry is a crucial problem quenching ignition in the field of inertial confinement fusion. A forward-calculation method based on 1D and 2D hydrodynamic simulations has been developed to generate and study the x-ray images of hot-spot self-emission, indicating asymmetry integrated over the entire drive pulse. It is shown that the x-ray imaging photon energy should be higher to avoid the influence of the remaining shell. The contour level (percentage of the maximum emission intensity) and spatial resolution should be as low as possible, optimally less than 20% and 3 µm, for characterization of higher-mode signatures such as P8–P12 by x-ray self-emission images. On the contrary, signatures of lower-mode such as P2 remain clear at all contour levels and spatial resolutions. These key results can help determine the optimal diagnostics, laser, and target parameters for implosion experiments. Recent typical hot-spot asymmetry measurements and applications on the Shenguang 100 kJ class laser facility are also reported.

Effect of crystals’ surface shape distortion on conversion efficiency of third harmonic generation

In the field of inertial confinement fusion (ICF), UV laser can effectively improve the beam-target coupling efficiency and suppress the hydrodynamic instability of laser plasma interaction. Using large aperture KDP crystal or KD*P crystal to triple the frequency of laser created by high power solid-state laser facility (wavelength is 1 μm) is an effective way to obtain high power UV laser output. At present, most high power laser facilities take method of I/II type third harmonic generation. The phase matching condition is required in the third harmonic generation, and the conversion efficiency is easily influenced by the detuned angle of crystals. The quality of the return light spot of crystals’ surface can reflect the state of wavefront distortion, and then evaluate the degree of angle-detuning at the crystal. The factors which create detuned angle are analyzed and judged, within which the surface shape distortion of crystals (PV is more than 30 μm) caused by clamping and gravity is the main part. According to improving the surface shape of crystals (PV is less than 10 μm) in the experiment, the quality of the return light spot of crystals has been significantly improved, and then the conversion efficiency of third harmonic generation has an obvious increase.

Inertial confinement fusion for energy: overview of the ongoing experimental, theoretical and numerical studies

This paper provides an overview of the results presented at the 26th IAEA Fusion Energy Conference in the field of inertial confinement fusion for energy, covering its various experimental, numerical/theoretical and technological facets, as well as the different paths towards ignition that are currently followed worldwide.

Experimental study on the incident-angle-dependent laser coupling features of polystyrene targets

Laser-produced plasmas have attracted great interest due to their potential utility in wide-ranging applications, especially in the field of inertial confinement fusion (ICF). For direct-driven ICF, laser coupling with polystyrene targets is a crucial and fundamental problem. In addition, oblique incidence is also a common phenomenon for laser facilities with multiple beams. It is necessary to evaluate the effects of oblique incidence on the laser coupling features relevant to the direct-driven ICF. Experiments using an intense nanosecond flat-top laser at around W cm–2 to irradiate polystyrene planar targets from three different incidence angles have been performed on the Shenguang-III prototype laser facility. The time-integrated absolute values of the full aperture backscatter (FABS), near backscatter scattering (NBS), and the x-ray conversion efficiency (CE) have been measured quantitatively. According to the experimental results, with the increase of the incidence angle, the percentage of the stimulated Brillouin backscatter and the overall x-ray CE decreased while the stimulated Raman backscatter fraction rose. Theoretical analyses based on hydrodynamic simulations and linear theory were qualitatively consistent with the experimental results. In addition, the specularly reflected light was also observed at 30° laser oblique incidence.

Boron carbide ceramic hollow microspheres prepared from poly(6-CH2[dbnd]CH(CH2)4-B10H13) precursor

Millimeter-sized boron carbide ceramic hollow microspheres have promising practical application in the encapsulation of nuclear fusion materials in the field of inertial confinement fusion. However, the fabrication of millimeter-sized compact boron carbide ceramic hollow microspheres from poly(6-hexenyldecaborane) precursor has not been reported yet. In this work, poly(6-hexenyldecaborane)s with decaborane in the main chain and the branched chain, respectively, were synthesized using 6-CH2CH(CH2)4-B10H13 as the monomer. Furthermore, compact boron carbide ceramic hollow microspheres were fabricated by the combination of emulsification-solvent evaporation technique and precursor derived method. With smooth surface and good sphericity, the hollow ceramic microspheres had an average outer diameter of 1.0mm and shell thickness ranging from 15 to 30μm.

$$\mathrm{ND}^2\mathrm{AV}$$ ND 2 AV : N-dimensional data analysis and visualization analysis for the National Ignition Campaign

One of the biggest challenges in high-energy physics is to analyze a complex mix of experimental and simulation data to gain new insights into the underlying physics. Currently, this analysis relies primarily on the intuition of trained experts often using nothing more sophisticated than default scatter plots. Many advanced analysis techniques are not easily accessible to scientists and not flexible enough to explore the potentially interesting hypotheses in an intuitive manner. Furthermore, results from individual techniques are often difficult to integrate, leading to a confusing patchwork of analysis snippets too cumbersome for data exploration. This paper presents a case study on how a combination of techniques from statistics, machine learning, topology, and visualization can have a significant impact in the field of inertial confinement fusion. We present the $$\mathrm{ND}^2\mathrm{AV}$$ : N-dimensional data analysis and visualization framework, a user-friendly tool aimed at exploiting the intuition and current workflow of the target users. The system integrates traditional analysis approaches such as dimension reduction and clustering with state-of-the-art techniques such as neighborhood graphs and topological analysis, and custom capabilities such as defining combined metrics on the fly. All components are linked into an interactive environment that enables an intuitive exploration of a wide variety of hypotheses while relating the results to concepts familiar to the users, such as scatter plots. $$\mathrm{ND}^2\mathrm{AV}$$ uses a modular design providing easy extensibility and customization for different applications. $$\mathrm{ND}^2\mathrm{AV}$$ is being actively used in the National Ignition Campaign and has already led to a number of unexpected discoveries.

Dynamic range of X-ray streak camera affected by space charge effect

x ray streak camera is an important equipment for time resolved measurement in the field of inertial confinement fusion. Its dynamic range indicates the ability that effectively measuring the intensity of incidence x ray. The photoelectron pulse will be broaden in passing through the photocathode-to-mesh region because of space charge effect. This limits the dynamic range of the streak camera. This paper adopts a fluid model, making use of particle conservation, momentum conservation, and Poisson equations to deduce the widening of the electron pulse and derive the change in the electron density distribution. The results can be used to evaluate the dynamic range of the streak camera.

Spectroscopic determination of temperature and density spatial profiles and mix in indirect-drive implosion cores

In the field of inertial confinement fusion (ICF), work has been consistently progressing in the past decade toward a more fundamental understanding of the plasma conditions in ICF implosion cores. The research presented here represents a substantial evolution in the ability to diagnose plasma temperatures and densities, along with characteristics of mixing between fuel and shell materials. Mixing is a vital property to study and quantify, since it can significantly affect implosion quality. We employ a number of new spectroscopic techniques that allow us to probe these important quantities. The first technique developed is an emissivity analysis, which uses the emissivity ratio of the optically thin Lybeta and Hebeta lines to spectroscopically extract temperature profiles, followed by the solution of emissivity equations to infer density profiles. The second technique, an intensity analysis, models the radiation transport through the implosion core. The nature of the intensity analysis allows us to use an optically thick line, the Lyalpha, to extract information on mixing near the core edge. With this work, it is now possible to extract directly from experimental data not only detailed temperature and density maps of the core, but also spatial mixing profiles.