The laser-driven flyer plate is an important loading technology in high energy physics, shock wave physics, and explosive initiation application. How to generate a high-velocity and intact flyer plate by using the laser is a matter of concern for laser driving. In this study, the multilayer flyer plates (MFPs) of Al/Al2O3/Al and TiO2/Al/Al2O3/Al with adjustable performance were designed and fabricated by magnetron sputtering and analyzed by scanning electron microscopy (SEM), laser reflectance spectrometer, and differential thermal analysis (DTA). The effects of the structure and material on the output performance of MFPs were analyzed by photon Doppler velocimetry (PDV) and ultrahigh-speed video. The morphology results showed that the structure of MFPs had uniform and clear boundaries between side-by-side layers. The MFP velocity was controlled in the range of 4.0–6.0 km/s by adjusting the film thickness, structure, and thermite material with 43.1 J/cm2 laser ablation. Among them, the energetic flyers with the thermite ablation layer had the highest final velocity of 5.38 km/s due to the prestored energy of TiO2/Al. By appropriately increasing the thickness of Al2O3 from 0.4 μm to 0.8 μm, the complete flight of the flyer plate to 3.72 mm can be realized. In addition, TiO2/Al thermite film had characteristics of reaction heat release and lower laser reflectivity (72.13%) than the Al layer (80.55%), which explained the velocity enhancement effect of energetic flyer plates. This work provides facile strategy to enhance the output performance of MFPs, which may facilitate the practical applications of laser driving technology.

The effects of magnetic vortex acceleration (MVA) are investigated with two-dimensional particle-in-cell (PIC) simulations by laser interaction with near-critical density (NCD) plasma inside a hollow conical plasma. Energetic and collimated proton beams can be accelerated by a longitudinal charge-separation field. Energetic protons with a peak energy of 220 MeV are produced in PIC simulations. Compared with a uniform NCD plasma, both the cutoff energy and collimation of proton beams are improved remarkably. Furthermore, the influence of different gap sizes of cone tip is taken into account. For optimizing magnetic vortex acceleration, the gap size of the cone tip is suggested to match the focal spot size of laser pulse.

Relativistic surface high harmonics, combined with the use of polarization gating, present a promising route towards intense single attosecond pulses. However, they impose stringent requirements on ultra-high laser contrast and are restricted by large intensity losses in real experiments. Here, we numerically demonstrate that by setting an optimal time delay in the polarization gating scheme, the intensity of the generated single attosecond pulses can become approximately 100 times stronger than that with nonoptimal time delay in the coherent synchrotron emission process. When a petawatt-class driving laser irradiates a solid target, an ultra-dense electron nanobunch and a strong space-charge sheath develop, and the accumulated electrostatic energy is only released in half of the laser cycle when this electron nanobunch moves backward. This process results in the emission of intense high harmonics. Our study provides a reliable method for developing bright attosecond extreme ultraviolet pulses.

The self-focusing/defocusing of Hermite-sinh-Gaussian (HshG) laser beam in underdense inhomogeneous plasmas is studied by using higher-order approximation theory. It is found that Hermite mode index and the fluctuation of the periodic plasma density have a significant effect on the dielectric constant and laser beam self-focusing/self-defocusing. With the increase of mode index, the high-order HshG laser beam is beneficial to suppress self-focusing and enhance self-defocusing. In addition, the effects of decentered parameters, beam intensity, and plasma non-uniformity on self-focusing/self-defocusing are discussed.

Radio frequency (RF) breakdown can result in pulse shortening and seriously degrade the stability and reliability of relativistic backward wave oscillators (RBWOs). This paper discusses the energy range of electrons causing breakdown traces in slow-wave structures (SWSs) through particle-in-cell (PIC) simulation, numerical calculation, and experimental verification. The PIC simulation and numerical calculation results reveal that the energy of the majority of the field-induced electrons bombarding the SWS surfaces after being accelerated is less than 120 keV. Furthermore, the micro appearances of the breakdown traces in SWSs and the witness targets bombarded directly by electrons of various energy levels have been analyzed. Scanning electron microscope (SEM) shows that the breakdown traces are featured with corrugated morphologies with a wide range and a shallow depth. A mass of craters emerge in the vicinity of the corrugated morphologies. These appearances are quite similar to destructive traces impacted directly by low-energy electrons (around 160 keV). Thus, it is confirmed that the breakdown traces result from the bombardment of low-energy electrons. Therefore, the breakdown mechanism of field-emitted electrons impacting on the structure surfaces in RBWOs has been further improved.

Femtosecond laser ablation is widely applied in high-precision machining of microholes in aeroengine turbine blades. To further explore the mechanism of action during the laser processing of microholes, numerical simulations were performed on the basis of a molecular dynamics (MD) method coupled with a two-temperature model (TTM). Laser irradiation on the surface of copper for different femtosecond-laser processing parameters is investigated in this work. Through the femtosecond-laser single-pulse central ablation simulation model, the laser energy flux density in a Gaussian laser spot range was discretized and analyzed to calculate the ablation depth at multiple points separately. The cross-sectional morphology of the femtosecond-laser single-pulse ablation pits was approximated and fitted. Finally, a 3D simulation model of the whole process of multiscale femtosecond-laser spiral processing microholes was established by superimposing multipulse femtosecond-laser spiral trajectories. This provides a theoretical basis for analyzing the evolution of geometric parameters and morphological characteristics of the hole during machining with specific laser and process parameters.

The Lawson criterion for proton-boron (p-11B) thermonuclear fusion is substantially higher than that for deuterium-tritium (DT) because the fusion cross section is lower and peaks at higher ion energies. The Maxwellian averaged p-11B reactivity peaks at several hundred keV, where bremsstrahlung radiation emission may dominate over fusion reactions if electrons and ions are in thermal equilibrium and the losses are unrestricted. Nonequilibrium burn has often been suggested to realize the benefits of this aneutronic reaction, but the predominance of elastic scattering over fusion reactivity makes this difficult to achieve. The development of ultrashort pulse lasers (USPL) has opened new possibilities for initiating nonequilibrium thermonuclear burns and significant numbers of p-11B alpha particles have been reported from several experiments. We present an analysis that shows that these significant alpha yields are the result of beam fusion reactions that do not scale to net energy gain. We further find that the yields can be explained by experimental parameters and recently updated cross sections such that a postulated avalanche mechanism is not required. We use this analysis to understand the underlying physics of USPL-driven nonequilibrium fusion reactions and whether they can be used to initiate fusion burns. We conclude by outlining a path to increasing the p-11B reactivity towards the goal of achieving ignition and describing the design principles that we will use to develop a computational point design.

A low-energy proton accelerator named pulsed synchronous linear accelerator (PSLA) is proposed and developed at the Institute of Fluid Physics, which is driven by unipolar-pulsed high voltages. Pulsed-accelerating electric fields and low-energy ion beams are precisely synchronized on temporal and spatial positions for continuous acceleration. The operating mode and the features of the PSLA are introduced. At present, the feasibility of a low-energy proton PSLA has been verified in principle. An average accelerating gradient up to 3 MV/m for protons is achieved.

With the advantages of short duration and extreme brightness, laser proton accelerators (LPAs) show great potential in many fields for industrial, medical, and research applications. However, the quality of current laser-driven proton beams, such as the broad energy spread and large divergence angle, is still a challenge. We use numerical simulations to study the propagation of such proton bunches in the plasma. Results show the bunch will excite the wakefield and modulate itself. Although a small number of particles at the head of the bunch cannot be manipulated by the wakefield, the total energy spread is reduced. Moreover, while reducing the longitudinal energy spread, the wakefield will also pinch the beam in the transverse direction. The space charge effect of the bunch is completely offset by the wakefield, and the transverse momentum of the bunch decreases as the bunch transports in the plasma. For laser-driven ion beams, our study provides a novel idea about the optimization of these beams.