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We theoretically and numerically study the merger phenomenon of the ion-phase vortex structure in hydrogen plasma. The results indicate that the merging of vortex structures during the nonlinear evolution of ion-acoustic waves (IAW) is mainly due to two-ion decay (TID) instability. When the daughter IAWs of the TID grow to be comparable to the fundamental mode, vortex merging will occur. Furthermore, the vortex merging can abruptly convert the significant energy of the fundamental mode into subharmonic energy, resulting in saturation for the TID of the fundamental mode. After several vortex-merging processes, the system eventually evolves into a turbulent state. In particular, the TID growth rate has been improved by considering two additional second-order coupling terms in this paper, which agree much better with the simulation results. Finally, the importance of the electron kinetic effects in the TID process is also presented by comparing hybrid-Vlasov and full-Vlasov simulations.

This study proposes a novel method to mitigate stimulated Brillouin scattering (SBS) using multicolor alternating-polarization bundle light. The bundle light combines multiwavelength, spike trains of uneven duration and delay for a single beam to multicolor alternating polarization for bundle beams. SBS suppression is verified using a three-dimensional large-scale laser plasma code. The numerical results show that the SBS reflectivity can be decreased by nearly two orders in low density plasma. The proposed method can extend the repetition time of a single beam from several picoseconds to tens of picoseconds. Moreover, it has potential applications in inertial confinement fusion research.

A one-third triangular resonator with two electric walls and two virtual magnetic walls is used to realize a compact wideband bandpass filter. This structure is fulfilled by taking out an isosceles or equilateral triangular resonator of substrate integrated waveguide (SIW) version and therefore, it is called one-third-mode substrate integrated resonator (OTMSIR). Based on one single cavity, a quadruple-mode technique is used to design a compact filter by adding an elliptical metallic via-hole and using detected ground structure (DGS). Finally, a 12.6 GHz bandwidth planar quadruple-mode filter is fabricated and tested. The measured results agree well with the simulated ones. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1993–1996, 2016

A target composition scheme to optimize the combined proton acceleration regime is presented and verified by two-dimensional particle-in-cell (2D PIC) simulations by using an ultra-intense circularly-polarized (CP) laser pulse irradiating an overdense hydrocarbon (CH) target, instead of a pure hydrogen (H) one. The combined acceleration regime is a two-stage proton acceleration scheme combining the radiation pressure dominated acceleration (RPDA) stage and the laser wakefield acceleration (LWFA) stage sequentially together. With an ultra-intense CP laser pulse irradiating an overdense CH target, followed by an underdense tritium plasma gas, protons with higher energies (from about $20$ GeV up to about $30$ GeV) and lower energy spreads (from about $18\%$ down to about $5\%$ in full-width at half-maximum, or FWHM) are generated, as compared to the use of a pure H target. It is because protons can be more stably pre-accelerated in the first RPDA stage when using CH targets. With the increase of the carbon-to-hydrogen density ratio, the energy spread is lower and the maximum proton energy is higher. It also shows that for the same laser intensity around $10^{22}$ $Wcm^{-2}$, using the CH target will lead to a higher proton energy, as compared to the use of a pure H target. Additionally, proton energy can be further increased by employing a longitudinally negative gradient of a background plasma density., Comment: 16 pages, 8 figures

Terahertz gyrotrons in harmonic operation offer the magnetic-field reduction, but they can also still easily generate various competing modes that operate at low harmonics. In this paper, an injection-locking technique for phase control and spectral purity is employed to enhance the operating modes and suppress the competing modes in gyrotrons. The simulation results, using a multi-mode time-independent code, show that gyrotrons driven by backward or forward waves cannot avoid mode competition wherever the input power increases. To avoid the fundamental harmonic competing mode, a second-harmonic gyrotron traveling-wave amplifier (gyro-TWA) with a severed section is used instead of the driven gyrotrons. The gyro-TWA operates at a slightly low external magnetic field and has a uniform interaction structure. The simulation results reveal that the fundamental harmonic TE3,5 competing mode does not occur at Ib

The anti-Stokes scattering and Stokes scattering in stimulated Brillouin scattering (SBS) cascade have been researched by the Vlasov-Maxwell simulation. In the high-intensity laser-plasmas interaction, the stimulated anti-Stokes Brillouin scattering (SABS) will occur after the second stage SBS rescattering. The mechanism of SABS has been put forward to explain this phenomenon. And the SABS will compete with the SBS rescattering to determine the total SBS reflectivity. Thus, the SBS rescattering including the SABS is an important saturation mechanism of SBS, and should be taken into account in the high-intensity laser-plasmas interaction., Comment: 6 pages, 5 figures

Slow-time-scale magnetic fields driven by fast-time-scale electromagnetic waves or plasma waves are examined from the perspective of the Vlasov–Maxwell equations for a relativistic Vlasov plasma. An equation for slow-time-scale magnetic field is obtained. The field proposed in the present paper is a result of wave–wave beating which drives a solenoidal current. The magnitude of the slow-time-scale magnetic field proposed here can be as high as 20 MG at the critical surface for a laser intensity I=1018 W/cm2 at wavelength λ0=1.05 μm. The predicted magnetic field is observed in two-dimensional particle simulations presented here.

It is shown that well collimated mono-energetic ion beams with a large particle number can be generated in the hole-boring radiation pressure acceleration regime by using an elliptically polarized laser pulse with appropriate theoretically determined laser polarization ratio. Due to the $\bm{J}\times\bm{B}$ effect, the double-layer charge separation region is imbued with hot electrons that prevent ion pileup, thus suppressing the double-layer oscillations. The proposed mechanism is well confirmed by Particle-in-Cell simulations, and after suppressing the longitudinal double-layer oscillations, the ion beams driven by the elliptically polarized lasers own much better energy spectrum than those by circularly polarized lasers., 6 pages, 5 figures, Phys. Plasmas (2013) accepted

The experiment results on spontaneous magnetic fields given by Najmudin et al. [Phys. Rev. Lett. 87, 215004 (2001)] can be explained by the kinetic model proposed by the present authors [Phys. Plasmas 8, 312 (2001)]. The dependence of the peak spontaneous magnetic field on the laser intensity is discussed. It is found the ratio of the number of thermal electrons to the total number of electrons is an important parameter.

Relativistic electromagnetic penetration behavior is reexamined in the relativistic transparency region. The interaction is modeled by the relativistic hydrodynamic equations coupled with the full system of Maxwell equations, which are solved by a fully implicit energy-conserving numerical scheme. For the first time, we have studied the penetration behavior through ultra-short circularly polarized and linearly polarized laser pulses interaction with over-dense plasmas. It is shown that for the ultra-short circularly polarized laser penetration occurs through a soliton like behavior, which is quite consistent with the existing studies. However, we have found that the ultra-short linearly polarized laser penetrates through a breather like behavior, and there is an energy transition mechanism with a frequency $2\omega_0$ between the penetrated breather like structure and the background plasmas. A qualitative interpretation has been given to describe this mechanism of energy exchange., Comment: 6 pages, 6 figures, submitted to Phys. Plasmas

It is first shown from the modulation instability of the conserved Zakharov equations (ZE) that spatiotemporal chaos is formed in the different regions of the unstable wave numbers. We find that chaos sets in when two homoclinic structures are present and then many and continual homoclinic crossings occur throughout the time series. It is shown that the presence of a homoclinic structure is a potential source of both temporal chaos and spatial patterns.

The dynamics of the ultra-intense circularly polarized solitons under inhomogeneous plasmas are examined. The interaction is modeled by the Maxwell and relativistic hydrodynamic equations and is solved with fully implicit energy-conserving numerical scheme. It is shown that a propagating weak soliton can be decreased and reflected by increasing plasma background, which is consistent with the existing studies based on hypothesis of weak density response. However it is found that ultra-intense soliton is well trapped and kept still when encountering increasing background. Probably, this founding can be applied for trapping and amplifying high-intensity laser-fields., Comment: 4 pages, 3 figures, submitted to Phys. Plasmas

Stimulated Brillouin back-scattering in mixed carbon and hydrogen plasmas is studied using one-dimensional Vlasov–Maxwell simulation. It is found that both the fast and slow ion acoustic waves can scatter the incident light. Carbon ions can be trapped in the slow ion acoustic wave, and the hydrogen ions can be trapped in both the fast and slow waves. The trapped ions tend to reduce the Landau damping of the ion acoustic waves, and both the fast and slow ion acoustic waves can be excited. From the time-integrated scattering spectra, the scattering peaks of the fast and slow ion acoustic waves can be clearly distinguished.

The excitation of terahertz radiation by stimulated Raman scattering is considered. Vlasov–Maxwell numerical simulations show that powerful terahertz radiation can be produced by cascade Raman scatterings.

The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov–Maxwell numerical simulation. It is found that the backward stimulated Raman scattering will be enhanced by electron-ion collisions. With appropriate electron-ion collision rate the Langmuir waves, driven via SRS, can be made to propagate for a long distance.

The evolution of high current electron beams in dense plasmas has been investigated by using two-dimensional particle-in-cell (PIC) simulations with immobile ions. It is shown that electron beams are split into many filaments at the beginning due to the Weibel instability, and then different filamentation beams attract each other and coalesce. The profile of the filaments can be described by formulas. Hammer et al. [Phys. Fluids 13, 1831 (1970)] developed a self-consistent relativistic electron beam model that allows the propagation of relativistic electron fluxes in excess of the Alfven-Lawson critical-current limit for a fully neutralized beam. The equilibrium solution has been observed in the simulation results, but the electron distribution function assumed by Hammer et al. is different from the simulation results.

The influence of self-generated magnetic and electric fields on the transport of relativistic electrons in dense plasmas was studied using a particle-in-cell simulation. For conditions relevant to the fast igniter, the laser-driven relativistic electrons may, have significant energy spread along or perpendicular to the propagation direction of the beams. The effect of electron energy spread on the growth rate. the occurrence threshold of both the Weibel-like filamentation instability and the electrostatic two-stream instability and the competition between them were investigated. The Weibel instability results in the formation of a magnetic channel, which may collimate inward fast electrons without significant deviation, and the excitation of a longitudinal electric field due to two-stream instability is destructive to the stability of the magnetic channel. The generation of relativistic electrons by the interaction of a high-intensity laser beam at the vacuum-dense plasma boundary and propagation of the electrons in the dense plasma were studied using a three-dimensional particle-in-cell code. It is shown that the electron velocity spread owing to transverse collective heating saturates the magnetic field and the longitudinal electrostatic field may play a dominant role in limiting the stable propagation of fast electrons into over-dense plasmas.