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In laser-driven inertial fusion, drive pressure boosting and smoothing to suppress hydrodynamic instabilities are major challenge. A proposed hybrid-drive (HD) scheme of a coupling of the indirect-drive (ID) and direct-drive (DD) offers two new effects, ″bulldozer″ like and thermal smoothing, to boost and smooth the HD pressure far greater than the radiation ablation pressure to perform stable implosion and nonstagnation ignition. In this article, we report that such HD pressure was first verified experimentally by a planar ablator target in a semicylindrical hohlraum. Using laser energy of 43 kJ for ID and 3.6-4.0 kJ (intensity about 1.8×1015 W⁄cm2 ) for DD, the HD pressure measured by VISAR is about 3.5 times the radiation ablation pressure with measured radiation temperature 200 eV(peak) by FXRD. How the symmetric HD shock driven by the HD pressure catches up with and stops the asymmetric ID shock is observed as well. While total fractions for DD laser backscattering and hot electron energy about 4.5% and about 2%, respectively, both about one-third of the traditional DD for the same intensity, are measured.

Effects of solid nanolayers embedded in a near-critical density plasma on the laser-driven collisionless shock acceleration are investigated by using two-dimensional particle-in-cell simulations. Due to the interaction of nanolayers and the incident laser, an additional number of hot electrons are generated and an inhomogeneous magnetic field is induced. As a result, the collisionless shock is reinforced within the nanolayer gaps compared to the target without the structured nanolayers. When the laser intensity is 9.8 × 10 19 W / cm 2 , the amplitude of the electrostatic field is increased by 30% and the shock velocity is increased from 0.079c to 0.091c, leading to an enhancement of the peak energy and the cutoff energy of accelerated protons, from 6.9 MeV to 9.1 MeV and 12.2 MeV to 20.0 MeV, respectively. Furthermore, the effects of the width of the nanolayer gaps are studied, by adjusting the gap width of nanolayers, and optimal nanolayer setups for collisionless shock acceleration can be acquired.

One of the most promising approaches to reach a high gain in inertial confinement fusion is the fast ignition scheme. In this scheme, a relativistic electron beam is generated; this passes through the imploded plasma and deposits parts of its energy in the core. However, the large angular spread of the relativistic electron beam and the poorly controlled compression of the target affect realization of the fast ignition technique. Here, we demonstrate that indirectly driven (that is, driven by X-rays generated inside a gold hohlraum) implosions with a ‘high-foot’ and a short-coast time of less than 200 ps allow us to tightly compress the shell. Furthermore, we show the ability to optimize the symmetry of the imploding shell by changing the hohlraum length, successfully tuning a suitable tube-shaped shell to compensate for the large angular spread of the relativistic electron beam and to enhance the electron-to-core coupling efficiency via resistive magnetic fields. Benefiting from those experimental techniques, a significant enhancement in neutron yield was achieved in our indirectly driven fast ignition experiments. These results pave the way towards high-coupling fast ignition experiments with indirectly driven targets similar to those at the National Ignition Facility. Experiments realizing the indirect-drive fast ignition scheme for inertial confinement fusion are reported. Enabled by a tightly compressed target, an increase of neutron yield is observed.

The rescattering of backward stimulated Raman scattering (BSRS) by stimulated Brillouin scattering (SBS) is found in the high electron density region by relativistic Vlasov-Maxwell simulation and particle-in-cell (PIC) simulation, where the BSRS is in the regime of absolute instability and dominates in all the scatterings. Both one dimension (1D) Vlasov simulation and two dimension (2D) PIC simulation have been given to verify that there exists SBS of BSRS in the regime of absolute instability for BSRS. The SBS of BSRS will be even stronger than forward stimulated Raman scattering (FSRS) and SBS in regime of absolute instability for BSRS. Thus, besides Langmuir decay instability and laser energy absorption, the SBS of BSRS is also an important saturation mechanism of BSRS in high electron density region.

Recent experiments reported the puzzling zero energy modes associated with ferromagnetic impurities in some iron-based superconductors with topological band structures. Here, we show that the sufficiently strong exchange coupling between a ferromagnetic impurity and substrate can trigger a quantum phase transition, beyond which, the phase of the topological surface superconducting order parameter around the impurity acquires a sign-change. In such a case, we prove that a Kramers degenerate pair of Majorana modes can be induced at the boundary separating the two sign-change regimes and trapped around the impurity in the topological surface superconducting state. Furthermore, we show that our theory can explain the controversial observations and confusing features of the zero energy modes from recent experiments in some iron-based superconductors., Comment: 6+13 pages, 4+11 figures

It is experimentally reported that the stratified layer atop Earth’s outer core is hundreds of kilometers thick with a maximum sound velocity reduction of 0.3% relative to the preliminary reference Earth model. However, why the sound velocity atop the outer core is reduced remains theoretically unclear. In this paper, the Ni and vital light O in the outer core were both considered to have implications for the stratification of Earth’s core, including the stratification thickness and the sound velocity profile. Ab initio molecular dynamics simulations were performed on the Fe-Ni-O fluid under the conditions of Earth’s outer core, and the self-diffusion coefficients and ion-ion dynamic structure factors were calculated. The self-diffusion coefficient of O is (19.56±0.83)×10-9 m2s-1 at the core-mantle boundary. Combining the diffusion equation with the time evolution of the O self-diffusion coefficient, the calculated stratification thickness at present is 194.7 km. The calculated ion-ion dynamic structural factors indicate that the sound velocity in the outmost outer core near the stratified layer is 7.86 km/s. These results show that Fe-Ni-O is a possible composition of the stratified layer atop the outer core featuring an appropriate thickness and a reduced sound velocity, thereby shedding light on the dynamic behavior of Earth’s core.

The spherically convergent plasma fusion (SCPF) scheme is a robust approach to provide a high-brightness pulsed neutron source. The performance of the SCPF driven by the long-pulsed laser is investigated. The experiments, with the laser pulse duration in a range of 0.5 ns to 3 ns, were implemented on the ShenGuang-II Upgrade facility and a 100 kJ level laser facility. The intensity of the laser beam was about multiple 1014 W cm−2. The measured D–D reaction neutron yields were in a range of 7.3 × 108 to 1.01 × 1011, while the driven laser energies were in a range of 2.1 kJ to 100.5 kJ. The temporal self-emitted x-ray flux and image were measured. It showed that the plasma core could be maintained for a longer time in the long duration shots. The neutron reaction rate was measured on the 100 kJ level laser facility. The full width at half maximum reached about 1 ns in the shot with 2 ns duration laser. The scaling law of the measured yields with respect to the laser power and the pulse duration were presented. The neutron yield was able to be increased by increasing the power and extending the duration.

Laser-driven ion acceleration has attracted global interest for its potential towards the development of a new generation of compact, low-cost accelerators. Remarkable advances have been seen in recent years with a substantial proton energy increase in experiments, when nanometer-scale ultrathin foil targets and high-contrast intense lasers are applied. However, the exact acceleration dynamics and particularly the ion energy scaling laws in this novel regime are complex and still unclear. Here, we derive a scaling law for the attainable maximum ion energy from such laser-irradiated nanometer-scale foils based on analytical theory and multidimensional particle-in-cell simulations, and further show that this scaling law can be used to accurately describe experimental data over a large range of laser and target parameters on different facilities. This provides crucial references for parameter design and experimentation of the future laser devices towards various potential applications.

In this paper, we show that the Gouy phase shift plays a key role in the far-field waveform evolution of the reflected harmonic radiations from plasma surfaces driven by a relativistic Gaussian laser. With a proper adjustment of laser focal position away from the plasma surface, the inherent separations between the peaks of different harmonic carrier waves as well as the fundamental wave due to different wavelengths can be cleared away when they propagate from near to far field, since they experience the same Gouy phase shift of $\ensuremath{\pi}/2$. Using this method, intense attosecond pulses can be obtained in the far field with no need of any spectral filters. Three-dimensional particle-in-cell simulations show that far-field attosecond pulses with intensity of $4\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.2em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ ($2.56\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.2em}{0ex}}\mathrm{W/sr}$; 65 times increase) and duration of $76\phantom{\rule{0.2em}{0ex}}\mathrm{as}$ (50% decrease) can be obtained by lasers at intensities of ${10}^{21}\phantom{\rule{0.2em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. Such brilliant pulses with fully reserved spectra significantly benefit applications in attosecond science.

Matter and radiation at extremes 5(6), 064402 (2020). doi:10.1063/5.0014854, Published by AIP Publishing, Melville, NY

It is shown theoretically and by simulation that a Gaussian laser beam of relativistic intensity interacting with a uniform-thickness plasma slab of azimuthally varying density can acquire orbital angular momentum (OAM). During the interaction, the laser ponderomotive force and the charge-separation force impose a torque on the plasma particles. The affected laser light and plasma ions gain oppositely directed axial OAM, but the plasma electrons remain almost OAM free. High OAM conversion efficiency is achieved due to the strong azimuthal electromagnetic energy flow during the laser phase modulation. The present scheme should provide useful reference for applications requiring relativistic-intense vortex light.

The authors propose a scheme utilizing an underdense plasma of spiral thickness in generating relativistic vortex laser light with axial orbital angular momentum. The laser ponderomotive and the plasma charge-separation forces exert a torque on the plasma ions, resulting in creation of oppositely directed forces in the plasma ions and the laser light.

Optica 7(4), 355-358 (2020). doi:10.1364/OPTICA.385147, Published by OSA, Washington, DC

A configuration to identify the stochastic effect of the quantum radiation reaction is proposed, where electrons are put in a standing wave of two colliding ultraintense lasers. By comparing the simulation results of the semiclassical and quantum models, we find that if the semiclassical model is used, a particular trapping of electrons between two electric-field nodes is induced, which, however, does not exist once the correct quantum model is applied. This results in different features of the electron density, energy, and angular distributions, which can be measured in experiments.

Stimulated Raman scattering can occur near the quarter critical density in direct-drive fusions, and the frequency of Raman-scattered light is about half of the incident light frequency. The second harmonic of the Raman-scattered light can be produced due to the inhomogeneity density profile. It can serve as the seed of stimulated Brillouin scattering (SBS). When the second harmonic of stimulated Raman-scattered light propagates against the incident light, some components will match the frequency of backward SBS, and SBS is induced. Thus, SBS could be greatly enhanced.

In this work, we studied the stopping power of deuterium-tritium (DT) plasmas mixed with impurities to the injected charged particles. Based on the Brown-Preston-Singleton model, the analytical expression for the change ratio of stopping power (denoted by η) induced by impurities in DT plasmas is developed, in which both classical short-distance collision part and quantum correction contribution are purely linear response to the impurity concentration ξ_{X}, while the classical long-range collision brings about higher-order nonlinear response to ξ_{X}. Furthermore, the expression for change ratio of deposition depth (denoted by χ) of charged particles induced by impurities in DT plasmas is also derived. As applications, we systemically investigated the energy loss of α particles deposited into a hot dense DT plasma mixed with impurity X(X=C, Si, Ge), where the temperature and density of DT are smaller than 10 keV and 500 g/cm^{3} and the concentration of Xξ_{X} is less than 5%. The numerical results suggest that (i) for the case of C mixed into DT, both change ratios of stopping power and deposition depth of α particles (i.e., η and χ) are linear response to the concentration of C ξ_{C}; (ii) for the case of Si mixed into DT, the second-order nonlinear response of η and χ to ξ_{Si} cannot be ignored when the densities of DT are larger than 200 g/cm^{3}; and (iii) for the case of Ge mixed into DT, the second- and third-order nonlinear response of η and χ to ξ_{Ge} are very remarkable because of the higher ionization degree and heavier atomic mass of Ge. The formulas and findings in this work may be helpful to the research of internal confinement fusion (ICF) related implosion physics and may provide useful theoretical guidance and data for the design of ICF target.

Nowadays hydrodynamic equations coupled with external equation of states provided by quantum mechanical calculations is a widely used approach for simulations of macroscopic degenerate plasmas. Although such an approach is proven to be efficient and shows many good features, especially for large scale simulations, it encounters intrinsic challenges when involving kinetic effects. As a complement, here we have invented a fully kinetic numerical approach for macroscopic degenerate plasmas. This approach is based on first principle Boltzmann-Uhling-Uhlenbeck equations coupled with Maxwell's equation, and is eventually achieved via an existing particle-in-cell simulation code named LAPINS. In this approach, degenerate particles obey Fermi-Dirac statistics and nondegenerate particles follow the typical Maxwell-Boltzmann statistics. The equation of motion of both degenerate and nondegenerate particles are governed by long range collective electromagnetic fields and close particle-particle collisions. Especially, Boltzmann-Uhling-Uhlenbeck collisions ensure that evolution of degenerate particles is enforced by the Pauli exclusion principle. The code is applied to several benchmark simulations, including electronic conductivity for aluminium with varying temperatures from 2 eV to 50 eV, thermalization of alpha particles in a cold fuel shell in inertial confinement fusion, and rapid heating of solid sample by short and intense laser pulses.

A new method to reduce the stimulated Raman scattering (SRS) in inertial confinement fusion conditions is proposed by changing the incident light phase discretely. The proposal is first examined by three-wave coupling equations and then verified by Vlasov simulations. A remarkable decreasing in SRS reflectivity is observed when the period of phase changing is less than 2 π / γ , where γ is the growth rate of SRS. By contrast, some simulations with continuously changing phase of incident light are carried out to compare their influence on SRS. In addition, the proposal may suppress the stimulated Brillouin scattering.

Nuclear reactions in the plasma environment can be substantially different from those in conventional laboratory non-plasma cases, which have attracted considerable attention in the fields of fusion and astrophysics. To self-consistently model the nuclear reaction process during plasma dynamic evolution, an extended nuclear reaction calculation module is developed and included in two-dimensional particle-in-cell simulations. Through the self-consistent simulations, we systematically show that, apart from the plasma screening, the kinetic Weibel instability (WI) occurring in plasmas also results in significant enhancement of nuclear reactions, where the self-generated magnetic fields play a key role. Specifically, the self-generated magnetic fields in WI deflect ion motions, decreasing the relative velocity, and convert plasma kinetic energy to thermal energy, increasing the ion temperature. The simulation results show that, for the t ( d , n ) α reaction with a sharp resonance peak in the cross section, the reaction product yield is enhanced four times due to the WI. For nuclear reactions that have more prominent resonance peaks in the cross section, like 12 C ( p , γ ) 13 N , it is expected that such enhancements can reach up to one or several orders of magnitude.

AIP Advances 11(7), 075003 (2021). doi:10.1063/5.0051178, Published by American Inst. of Physics, New York, NY

We demonstrate theoretically and numerically that intense isolated circularly polarized (CP) attosecond pulses can be generated from ultrathin foil targets irradiated by two relativistic lasers from opposite sides, where their polarizations are orthogonal to each other. With a proper matching condition, the compressed oscillating plasma mirrors on both sides of the foil are pushed inside by laser radiation pressures, eventually merging together to form a dense electron nanobunch under the effect of orthogonal laser fields. This nanobunch reaches both high density and high energy in only half a laser cycle and smears out in others, resulting in coherent synchrotron emission of a single attosecond pulse with circular polarization. Two-dimensional particle-in-cell simulations show that an intense isolated CP attosecond XUV pulse with an intensity of 1.2 × 1019 W cm−2 and a duration of ∼75 as can be obtained by two lasers with the same intensity of 2.1 × 1020 W cm−2.

We present our recent laser-plasmas instability (LPI) comparison experiment at the SGIII laser facility between the spherical and cylindrical hohlraums. Three kinds of filling are considered: vacuum, gas-filling with or without a capsule inside. A spherical hohlraum of 3.6 mm in diameter, and a cylindrical hohlraum of 2.4 mm × 4.3 mm are used. The capsule diameter is 0.96 mm. A flat-top laser pulse with 3 ns duration and up to 92.73 kJ energy is used. The experiment has shown that the LPI level in the spherical hohlraum is close to that of the outer beam in the cylindrical hohlraum, while much lower than that of the inner beam. The experiment is further simulated by using our 2-dimensional radiation hydrodynamic code LARED-Integration, and the laser back-scattering fraction and the stimulated Raman scatter (SRS) spectrum are post-processed by the high efficiency code of laser interaction with plasmas HLIP. According to the simulation, the plasma waves are strongly damped and the SRS is mainly developed at the plasma conditions of electron density from 0.08 nc to 0.1 nc and electron temperature from 1.5 keV to 2.0 keV inside the hohlraums. However, obvious differences between the simulation and experiment are found, such as that the SRS back-scattering is underestimated, and the numerical SRS spectrum peaks at a larger wavelength and at a later time than the data. These differences indicate that the development of a 3D radiation hydrodynamic code, with more accurate physics models, is mandatory for spherical hohlraum study.

A compact laser plasma accelerator (CLAPA) that can stably produce and transport proton ions with different energies less than 10 MeV, $l1%$ energy spread, several to tens of pC charge, is demonstrated. The high current proton beam with continuous energy spectrum and a large divergence angle is generated by using a high contrast laser and micron thickness targets, which later is collected, analyzed and refocused by an image-relaying beam line using a combination of quadrupole and bending electromagnets. It eliminates the inherent defects of the laser-driven beams, realizes precise manipulation of the proton beams with reliability, availability, maintainability and inspectability (RAMI), and takes the first step towards applications of this new generation of accelerator. With the development of high-rep rate Petawatt (PW) laser technology, we can now envision a new generation of accelerator for many applications in the near future soon.

Plasma effects, such as the multi-component kinetic diffusion and self-generated electromagnetic fields, are recognized as a pivotal key to understanding the physics of interface evolution in inertial confinement fusion and supernova remnants. In this work, a two-dimensional hybrid fluid-PIC code is used to investigate the ion kinetic effects of the single-mode Richtmyer–Meshkov instability (RMI) at the interface between hydrogen plasma and carbon plasma. After an electrostatic shockwave passing through the perturbed interface, the RMI, which reshapes the interface, grows via the vorticity depositing as well as the self-generated magnetic field. After scaling the growth of the interfacial mix region with time, the density transition layer has been found to exceed the disturbance wavelength and lead to a suppression of the instability evolution finally.

Earth's magnetic field is generated by the liquid outer core and sensitively depends on the thermal conductivity of the core. The dominant component of the Earth's core is Fe (∼85%) and Ni (∼10%). However, current estimates on FeNi liquids have not been previously tested at high pressures. In this paper, ab initio simulations were first applied to calculations of the thermal and electrical conductivities of FeNi liquids at Earth's outer core conditions. The thermal conductivity along the adiabatic curve for FeNi fluid ranges from 120.52 to 202.80 W/m/K, but pure Fe ranges from 125.07 to 216.18 W/m/K. The age of the inner core calculated with thermal conductivity of FeNi fluid is 0.019 Ga longer than pure Fe. Nickel effect on the age of the inner core is of the same order with the uncertainty of density jump and latent heat at the inner-core boundary. Furthermore, by analyzing the effective temperature gradient, the present thickness of thermal stratification calculated with thermal conductivity of FeNi liquid is 64.5 km thinner than that of pure Fe.

Isolated attosecond pulses are useful to perform pump–probe experiments at a high temporal resolution, and provide a new tool for ultrafast metrology. However, it is still a challenging task to generate such pulses of high intensity, even for a few-cycle laser. Through particle-in-cell simulations, we show that it is possible to directly generate a giant isolated attosecond pulse in the transmission direction from relativistic laser-driven plasmas. Compared to attosecond pulse generation in the reflection direction, no further spectral filtering is needed. The underlying radiation mechanism is coherent synchrotron emission, and the transmitted isolated attosecond pulse can reach relativistic intensity. This provides a promising alternative to generate intense isolated attosecond pulses for ultrafast studies.

Through nonequilibrium molecular dynamics simulations, we provide an atomic-scale picture of the dynamics of particles near the surface of a medium under ultra-strong shocks. This shows that the measured surface velocity vf under ultra-strong shocks is actually the velocity of the critical surface at which the incident probe light is reflected, and vf has a single-peaked structure. The doubling rule commonly used in the case of relatively weak shocks to determine particle velocity behind the shock front is generally not valid under ultra-strong shocks. After a short period of acceleration, vf exhibits a long slowly decaying tail, which is not sensitive to the atomic mass of the medium. A scaling law for vf is also proposed, and this may be used to improve the measurement of particle velocity u in future experiments.

The effects of the subwavelength nanowire target on the enhanced laser absorption, heating of electrons, and acceleration and control of energetic ions are investigated by using two-dimensional particle-in-cell simulations. Compared with the flat target, the conversion efficiency and acceleration of target normal sheath acceleration can be improved remarkably. In the condition considered in this paper, the conversion efficiency from the laser to electrons can be increased by about four times (14.74% to 65.78%), and the cutoff energy of electrons can be raised by 1.5 times. Furthermore, the cutoff energies of both protons and carbon ions are increased by almost two times. The dependence of this effect for different nanowire widths is discussed by numerical simulations. It is found that the efficiency from the laser to electrons reaches the highest value when the nanowire width is d = 0.2 μ m. The optimum width for C6+ ions is d = 0.3 μ m, while d = 0.8 μ m is better for proton acceleration. Thus, the laser absorption, electron heating, and ion acceleration could be controlled by selecting the width of subwavelength nanowires.

In this paper, we give a review of our theoretical and experimental progress in octahedral spherical hohlraum study. From our theoretical study, the octahedral spherical hohlraums with 6 Laser Entrance Holes (LEHs) of octahedral symmetry have robust high symmetry during the capsule implosion at hohlraum-to-capsule radius ratio larger than 3.7. In addition, the octahedral spherical hohlraums also have potential superiority on low backscattering without supplementary technology. We studied the laser arrangement and constraints of the octahedral spherical hohlraums, and gave a design on the laser arrangement for ignition octahedral hohlraums. As a result, the injection angle of laser beams of 50°–60° was proposed as the optimum candidate range for the octahedral spherical hohlraums. We proposed a novel octahedral spherical hohlraum with cylindrical LEHs and LEH shields, in order to increase the laser coupling efficiency and improve the capsule symmetry and to mitigate the influence of the wall blowoff on laser transport. We studied on the sensitivity of the octahedral spherical hohlraums to random errors and compared the sensitivity among the octahedral spherical hohlraums, the rugby hohlraums and the cylindrical hohlraums, and the results show that the octahedral spherical hohlraums are robust to these random errors while the cylindrical hohlraums are the most sensitive. Up till to now, we have carried out three experiments on the spherical hohlraum with 2 LEHs on Shenguang(SG) laser facilities, including demonstration of improving laser transport by using the cylindrical LEHs in the spherical hohlraums, spherical hohlraum energetics on the SGIII prototype laser facility, and comparisons of laser plasma instabilities between the spherical hohlraums and the cylindrical hohlraums on the SGIII laser facility. PACS codes: 52.70.La, 52.35.Tc, 47.40.Nm, Keywords: Indirect-drive inertial confinement fusion, Novel spherical hohlraum with 6 LEHs, High and robust radiation symmetry, High energy coupling efficiency, Theoretical study, Experiments

The octahedral spherical hohlraums have natural superiority in maintaining high radiation symmetry during the entire capsule implosion process in indirect drive inertial confinement fusion. While, in contrast to the cylindrical hohlraums, the narrow space between the laser beams and the spherical hohlraum wall is usually commented. In this Letter, we address this crucial issue and report our experimental work conducted on the SGIII-prototype laser facility which unambiguously demonstrates that a simple design of cylindrical laser entrance hole (LEH) can dramatically improve the laser propagation inside the spherical hohlraums. In addition, the laser beam deflection in the hohlraum is observed for the first time in the experiments. Our 2-dimensional simulation results also verify qualitatively the advantages of the spherical hohlraums with cylindrical LEHs. Our results imply the prospect of adopting the cylindrical LEHs in future spherical ignition hohlraum design. PACS codes: 52.57.-z, 52.50.Jm, 52.38.Mf, Keywords: Spherical hohlraum, Laser propagation, Cylindrical laser entrance hole, Laser spot movement

The influence of low-mode-driven asymmetry on yield degradation in shaped-pulse indirect-drive implosions has been investigated at the 100 kJ laser facility. In this work, P2- and P4-driven asymmetries were tuned by varying hohlraum gas-fill density and capsule diameter. The measured neutron yield varied from 2.1 × 109 to 7.6 × 109 and the yield measured by a 1D simulation (YOC1D) was increased from 3% to 16%. Meanwhile, considering the temporal P2- and P4-driven asymmetries, the yields measured by 2D simulations (YOC2D) were from 26% to 81% (the YOC2D of the majority of the shots was higher than 50%). Furthermore, both the ion temperature and neutron bang-time showed good agreement between the measurements and the 2D simulations. The simulations demonstrated that the temporal P2- and P4-driven asymmetries can decrease the efficiency of PdV work and increase the energy loss due to electron thermal conduction. In addition, the internal energy of the deuterium (DD) fuel clearly decreased and the neutron yield was degraded by low-mode asymmetry. In a future work, we will enlarge the cylindrical hohlraum diameter or use an I-hohlraum to improve the low-mode-driven symmetry, along with measurement of the hot-spot shape.

High-order harmonic generation provides an opportunity for generating intense extreme ultraviolet attosecond pulses, which is useful to explore the property of materials. Transmitted radiation emitted by an ultrathin target illuminated by intense lasers is a promising way to generate such pulses. We show that the preplasma density gradient has an important influence on the transmitted radiation. An optimal scale length exists to support ultrathin nanobunches to generate coherent synchrotron emission and thus enormously enhance the radiation. Particle in cell simulations suggest that the optimal scale length depends on the laser intensity.

Kinetic physics has the potential to impact the performance of indirect-drive inertial confinement fusion (ICF) experiments. In near vacuum hohlraums (or vacuum hohlraums), the high-Z plasma expands from the hohlraum wall and collides with the blow-off from the capsule (or the low-density fill-gas). Such collision produces conditions in which kinetic effects may dominate since the ion-ion mean free paths are larger than the size of the interaction region. In the present work, we present the experimental evidence supported by simulations of kinetic effects launched in the interpenetration layer between the laser-driven hohlraum plasma bubbles and the corona plasma of the compressed pellet on the Shenguang-III prototype laser facility. Our study showed kinetic shocks arisen in the hohlraum wall/ablator (or the low-density fill-gas) interpenetration region, which result in efficient acceleration of high energy ions. When these high energy ions were deposited inside the capsule, it resulted in significant low-mode asymmetry of the implosion capsule since there are no high energy ions from the laser entrance holes. These studies provide novel insight into the interactions and dynamics of a vacuum hohlraum and near vacuum hohlraum.

Bright extreme ultraviolet (XUV) sources with elliptical polarization are powerful tools for investigating the electronic and magnetic properties of materials. Here we show that in the regime of relativistic electrons spring, it is possible to generate a source of elliptically polarized attosecond XUV pulses by a circularly polarized laser pulse interacting with near-critical density plasmas. Particle-in-cell simulations indicate that compared with a conventional overdense plasma regime, the attosecond pulse intensity may be increased by up to one order of magnitude in a near-critical density plasma system.

We use quantum molecular dynamics to systematically study the equation of state of 6LiD in the density range 1.76 to 3.68 g/cm3. The calculations involve the self-consistent determination of (a) the equation of state, (b) the principal and second-shocked Hugoniot curves, (c) the conductivity and reflectivity of the warm dense states, and (d) the electronic structure. Upon comparing our results with experiments, we find that the all-electron Li pseudopotential gives a better description of the second-shocked Hugoniot states than the Li pseudopotential with only 2s valence electrons. The optical conductivity increases with pressure along the principal Hugoniot curves. The atomic pair correlation functions reveal the order-to-disorder transition of 6LiD.

Interface width effect on the spherical Rayleigh–Taylor instability in the weakly nonlinear regime is studied by numerical simulations. For Legendre perturbation mode Pn with wave number kn and interface half-width L, the commonly adopted empirical linear growth rate formula γ n em ( L ) = γ n / 1 + k n L is found to be sufficient in spherical geometry. At the weakly nonlinear stage, the interface width affects the mode coupling processes. The development of the mode P 2n is substantially influenced by the interface width. Moreover, the nonlinear saturation amplitude increases with the interface width.

A new saturation mechanism, beam plasma instability with trapped electrons resulting in saturation of stimulated Raman backscattering (SRBS), is presented. The beam plasma instability can be excited due to interaction between beam electrons and background electrons and it will produce a new mode. Here, the trapped electrons can be considered as beam electrons with velocity vp(phase velocity of the plasma wave) and density nt (density of the trapped electrons normalized by nc, nc is the critical density for the incident laser light). This new mode will induce a sinusoidal density modulation and then this modulation will produce harmonic wave with modulation wave-number period δk to enhance this new mode. As reported previously, the density modulation can increase Landau damping of the plasma wave and decrease the resonant region where SRBS occurs. Therefore, SRBS will saturate due to beam plasma instability induced by the trapped electrons.

The Rayleigh–Taylor instability at the weakly nonlinear (WN) stage in spherical geometry is studied by numerical simulation. The mode coupling processes are revealed. The results are consistent with the WN model based on parameter expansion, while higher order effects are found to be non-negligible. For Legendre mode perturbation Pn (cosθ), the nonlinear saturation amplitude (NSA) of the fundamental mode decreases with the mode number n. When n is large, the spherical NSA is lower than the corresponding planar one. However, for large n, the planar NSA can be recovered by applying Fourier transformation to the bubble/spike near the equator and calculating the NSA of the converted trigonometric harmonic.

The two-laser entrance hole (LEHs) spherical hohlraum energetic experiments with all 48 laser beams and two laser pulse shapes at the 100 kJ level laser facility were investigated. In this work, the time-resolved radiation temperature measured by multi-angle x-ray diodes agreed well with LARED simulations, and the peak radiation temperature was up to 260 eV with the laser power of 45 TW. Meanwhile, the backscattered laser energy fraction was less than 5% in the majority of shots, which proposed a low level of laser–plasma interaction (LPI) effect in the spherical hohlraum. However, in the shaped pulse shots with capsules, the stimulated Raman scattering (SRS) of smaller incident angle lasers was significantly increased to 15%. The measured SRS spectrum and LARED simulations showed that the increase in the LPI effects caused by the ablated CH plasma was around 0.1Nc (Nc is the critical density). In summary, according to the experimental results, the x-ray conversion efficiency of the vacuum spherical hohlraum was 85%–88% in 3 ns square pulses and 89%–93% in 3.6 ns shaped pulses. It was closer to that of the two-LEH cylindrical hohlraum at the Shen-Guang and NIF facilities.