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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.

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.

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.

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.

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.

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.

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

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.

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.

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.

We investigate the high-order above-threshold ionization (HATI) of atoms (Ar and Xe) and molecules (N2 and O2) subjected to strong laser fields by numerically solving time-dependent Schrodinger equation. It is demonstrated that resonance-like enhancement of groups of adjacent peaks in photoelectron spectrum of HATI is observed for Ar, Xe, and N2, while this peculiar phenomenon is absent for O2, which is in agreement with experimental observation [ Phys. Rev. A88, 021401 (2013)]. In addition, analysis indicates that resonance-like enhancement in HATI spectra of atoms and molecules is closely related to excitation of the high-lying excited states.

Through the perturbation formula of time-dependent density functional theory broadly employed in the calculation of solids, we provide a first-principles calculation of x-ray Thomson scattering spectrum of isochorically heated aluminum foil, as considered in the experiments of Sperling et al. [Phys. Rev. Lett. 115, 115001 (2015)PRLTAO0031-900710.1103/PhysRevLett.115.115001], where ions were constrained near their lattice positions. From the calculated spectra, we find that the electronic temperature cannot exceed 2 eV, much smaller than the previous estimation of 6 eV via the detailed balance relation. Our results may well be an indication of unique electronic properties of warm dense matter, which can be further illustrated by future experiments. The lower electronic temperature predicted partially relieves the concern on the heating of x-ray free electron laser to the sample when used in structure measurement.

Matter and radiation at extremes 3(6), 293 - 299 (2018). doi:10.1016/j.mre.2018.06.002, Published by Elsevier, Amsterdam

Direct studies of intense laser-solid interactions is still of great challenges, because of the many coupled physical mechanisms, such as direct laser heating, ionization dynamics, collision among charged particles, and electrostatic or electromagnetic instabilities, to name just a few. Here, we present a full particle-in-cell simulation (PIC) framework, which enables us to calculate laser-solid interactions in a "first principle" way, covering almost "all" the coupled physical mechanisms. Apart from the mechanisms above, the numerical self-heating of PIC simulations, which usually appears in solid-density plasmas, is also well controlled by the proposed "layered-density" method. This method can be easily implemented into the state-of-the-art PIC codes. Especially, the electron heating/acceleration at relativistically intense laser-solid interactions in the presence of large scale pre-formed plasmas is re-investigated by this PIC code. Results indicate that collisional damping (even though it is very week) can significantly influence the electron heating/acceleration in front of the target. Furthermore the Bremsstrahlung radiation will be enhanced by $2\sim3$ times when the solid is dramatically heated and ionized. For the considered case, where laser is of intensity $10^{20}\ \text{W}/\text{cm}^2$ and pre-plasma in front of the solid target is of scale-length $10\ \mu\text{m}$, collision damping coupled with ionization dynamics and Bremsstrahlung radiations is shown to lower the "cut-off" electron energy by $25\%$. In addition, the resistive electromagnetic fields due to Ohmic-heating also play a non-ignorable role and must be included in real laser-solid interactions., Comment: 15 pages, 16 figures

Self-shaping and propagation of intense laser beams of different radial profiles in plasmas is investigated. It is shown that when a relativistic elliptically Gaussian beam propagates through an underdense plasma, its radial profile will self-organize into a circularly symmetric self-similar smooth configuration. Such self-similar propagation can be attributed to a soliton-like structure of the laser pulse. The anisotropic electron distribution results in a circular electric field that redistributes the electrons and modulates the laser pulse to a circular radial shape.

We investigate a new laser-driven spherically convergent plasma fusion scheme (SCPF) that can produce thermonuclear neutrons stably and efficiently. In the SCPF scheme, laser beams of nanosecond pulse duration and 10^{14}-10^{15} W/cm^{2} intensity uniformly irradiate the fuel layer lined inside a spherical hohlraum. The fuel layer is ablated and heated to expand inwards. Eventually, the hot fuel plasmas converge, collide, merge, and stagnate at the central region, converting most of their kinetic energy to internal energy, forming a thermonuclear fusion fireball. With the assumptions of steady ablation and adiabatic expansion, we theoretically predict the neutron yield Y_{n} to be related to the laser energy E_{L}, the hohlraum radius R_{h}, and the pulse duration τ through a scaling law of Y_{n}∝(E_{L}/R_{h}^{1.2}τ^{0.2})^{2.5}. We have done experiments at the ShengGuangIII-prototype facility to demonstrate the principle of the SCPF scheme. Some important implications are discussed.

We show a new resonance acceleration scheme for generating ultradense relativistic electron bunches in helical motions and hence emitting brilliant vortical γ-ray pulses in the quantum electrodynamic (QED) regime of circularly-polarized (CP) laser-plasma interactions. Here the combined effects of the radiation reaction recoil force and the self-generated magnetic fields result in not only trapping of a great amount of electrons in laser-produced plasma channel, but also significant broadening of the resonance bandwidth between laser frequency and that of electron betatron oscillation in the channel, which eventually leads to formation of the ultradense electron bunch under resonant helical motion in CP laser fields. Three-dimensional PIC simulations show that a brilliant γ-ray pulse with unprecedented power of 6.7 PW and peak brightness of 1025 photons/s/mm2 /mrad2 /0.1% BW (at 15 MeV) is emitted at laser intensity of 1.9 × 1023 W/cm2.

γ-ray flash generation in near-critical-density target irradiated by four symmetrical colliding laser pulses is numerically investigated. With peak intensities about 10^{23} W/cm^{2}, the laser pulses boost electron energy through direct laser acceleration, while pushing them inward with the ponderomotive force. After backscattering with counterpropagating laser, the accelerated electron is trapped in the electromagnetic standing waves or the ponderomotive potential well created by the coherent overlapping of the laser pulses, and emits γ-ray photons in a multiple-laser-scattering regime, where electrons act as a medium transferring energy from the laser to γ rays in the ponderomotive potential valley.

We demonstrate the instability-free ion acceleration regime by introducing laser control with two parallel circularly polarized laser pulses at an intensity of I = 6.8 × 1021 W/cm2, normally incident on a hydrogen foil. The special structure of the equivalent wave front of those two pulses, which contains Gaussian peaks in both sides and a concavity in the centre (2D), can suppress the transverse instabilities and hole boring effects to constrain a high density ion clump in the centre of the foil, leading to an acceleration over a long distance and gain above 1GeV/u for the ion bunches.

The anomalous mix at the high-Z and low-Z plasma interfaces in an inertial confinement fusion hohlraum is a current topic of interest. The mechanism for such an anomalous mix in the interpenetration layer at the high-Z and low-Z plasma interface and its effects on the laser plasma instabilities have been investigated by particle-in-cell simulations. It is found that a diffusion-driven collisionless shock wave can be generated from an initially sharp high-Z and low-Z plasma interface with total pressure balance and constant temperature in the laser propagation channel. This purely electrostatic shock wave propagates into the high-Z plasma and leads to mix of different species of ions which is significantly faster than a classical mix in the presence of the large electric field. The mix layer width, measured as a separation distance affected by the shock, grows as , where . The effect of the anomalous mix on the linear growth rate of laser plasma instabilities is evaluated.

Recently, radiation pressure acceleration (RPA) has been proposed and extensively studied, which shows that circularly polarized (CP) laser pulses can accelerate mono-energetic ion bunches in a phase-stable-acceleration (PSA) way from ultrathin foils. It is found that self-organizing proton beam can be stably accelerated to GeV in the interaction of a CP laser with a planar target at 1022 W/cm2. A project called Compact LAser Plasma proton Accelerator (CLAPA) is approved by MOST in China recently. A prototype of laser driven proton accelerator (1 to 15 MeV/1 Hz) based on the PSA mechanism and plasma lens is going to be built at Peking University in the next five years. It will be upgraded to 200 MeV later for applications such as cancer therapy, plasma imaging and fast ignition for inertial confine fusion.

In this research, the nonlinear evolution of jet-like spikes in the single-mode ablative Rayleigh-Taylor instability (ARTI) in the presence of preheating, is studied numerically. It is demonstrated that the preheating plays an essential role in the formation of jet-like spikes in the nonlinear ARTI. The evolution of jet-like spikes in the ARTI with preheating consists of three stages with distinctly different distinguishing features. In the early stage, the preheating contributes to significantly increase the density-gradient scale length and broaden the velocity profile of the ablation surface, where the former can reduce the linear growth of the ARTI and mitigate the growth of its harmonics. In the middle stage, the ablative Kelvin-Helmholtz instability is dramatically suppressed due to the ablation effects. In the late stage, the jet's length (i.e. bubble-spike amplitude) is further increased by the bubble acceleration in the highly nonlinear ARTI, resulting eventually in the formation of jet-like spikes.

A new inverse Compton scattering scheme for production of high-energy Gamma-ray sources is proposed in which a Giga-electronvolt (GeV) electron beam is injected into a thermal hohlraum. It is found that by increasing the hohlraum background temperature, the scattered photons experience kinematic pileup, resulting in more monochromatic spectrum and smaller scattering angle. When a relativistic electron beam with energy 1 GeV and charge 10nC is injected into a 0.5 keV hohlraum, 80% of the scattered photons have energy above 0.5 GeV.

We study statistics and structures of pressure and density in the presence of large-scale shock waves in a forced compressible isotropic turbulence using high-resolution numerical simulation. The spectra for pressure and density exhibit a −2 scaling over an operational definition of the inertial range. Both the numerical simulation and a heuristic PDF model reveal that the PDFs of pressure increment exhibit a −2 power law region for the separation in the operational definition of inertial range, quantitatively similar to the PDF of pressure gradient, which also displays a −2 power law region. Moreover, the statistical relation between density increment and pressure increment has been investigated through a shock-relation model. There is a positive correlation between the vorticity magnitude and pressure, which is different from the case of incompressible turbulence. We argue that this difference is due to large-scale shock waves, another type of intermittent structures in addition to vortex structures in ...

The driving mechanism of solar flares and coronal mass ejections is a topic of ongoing debate, apart from the consensus that magnetic reconnection plays a key role during the impulsive process. While present solar research mostly depends on observations and theoretical models, laboratory experiments based on high-energy density facilities provide the third method for quantitatively comparing astrophysical observations and models with data achieved in experimental settings. In this article, we show laboratory modeling of solar flares and coronal mass ejections by constructing the magnetic reconnection system with two mutually approaching laser-produced plasmas circumfused of self-generated megagauss magnetic fields. Due to the Euler similarity between the laboratory and solar plasma systems, the present experiments demonstrate the morphological reproduction of flares and coronal mass ejections in solar observations in a scaled sense, and confirm the theory and model predictions about the current-sheet-born anomalous plasmoid as the initial stage of coronal mass ejections, and the behavior of moving-away plasmoid stretching the primary reconnected field lines into a secondary current sheet conjoined with two bright ridges identified as solar flares.

We present a molecular dynamics simulation of shock waves propagating in dense deuterium with the electron force field method [J. T. Su and W. A. Goddard, Phys. Rev. Lett. 99, 185003 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.185003], which explicitly takes the excitation of electrons into consideration. Nonequilibrium features associated with the excitation of electrons are systematically investigated. We show that chemical bonds in D_{2} molecules lead to a more complicated shock wave structure near the shock front, compared with the results of classical molecular dynamics simulation. Charge separation can bring about accumulation of net charges on large scales, instead of the formation of a localized dipole layer, which might cause extra energy for the shock wave to propagate. In addition, the simulations also display that molecular dissociation at the shock front is the major factor that accounts for the "bump" structure in the principal Hugoniot. These results could help to build a more realistic picture of shock wave propagation in fuel materials commonly used in the inertial confinement fusion.

With $^{6}\mathrm{Li}\text{D}$ as an example, we show that the applicable region of the orbital-free molecular dynamics (OFMD) method in a large temperature range is determined by the thermal ionization process of bound electrons in shell structures. The validity boundary of the OFMD method is defined roughly by the balance point of the average thermal energy of an electron and the ionization energy of the lowest localized electronic state. This theoretical proposition is based on the observation that the deviation of the OFMD method originates from its less accurate description to the charge density in partially ionized shells, as compared with the results of the extended first-principles molecular dynamics method, which well reproduces the charge density of shell structures.