Xue-Ren Hong

Envelop solitons in dusty plasmas for warm dust

Abstract A nonlinear Schrodinger equation is obtained for the warm dusty plasmas. The modulational instability of envelop soliton is investigated in this paper. Both the temperature of the dust grains and the charge variations of dust grains affect the instability regions of the dusty plasmas. It also affect the amplitude and the width of the envelop soliton.

Solitary waves of laser pulse in a plasma channel

The propagation of a Gaussian laser pulse in a preformed plasma channel is investigated. The conditions for the existence of electromagnetic solitary waves are obtained theoretically by analyzing the differential equation of the pulse spot size including the effects of relativistic self-focusing, ponderomotive self-channeling, and preformed channel focusing. Some solitarylike wave solutions are presented numerically and their possible implications on laser-plasma acceleration are discussed briefly.

Electron trajectories and betatron oscillation in the wake bubble in laser-plasma interaction

The trajectories of electrons originating from different initial locations in the unperturbed plasma during the interaction of an ultraintense laser with underdense plasma in the bubble regime are followed by particle-in-cell simulation. It is found that plasma electrons initially aligned with the rim of the laser focal spot contribute most to the bow wave in front of the bubble and those aligned with the lateral bubble sheath edge contribute most to the self-injection at the back of the bubble. A scaling law between the transverse electric and magnetic fields for the case where there are many electrons in the bubble is given and discussed in terms of betatron oscillations of the injected electrons.

Investigation of superlubricity in a two-dimensional Frenkel-Kontorova model with square lattice symmetry

A two-dimensional Frenkel–Kontorova model with a square symmetry substrate potential for a square lattice layer driven by an external driving force with an arbitrary direction α and an arbitrary misfit angle θ between upper and lower layers is presented in this paper. The effects of the system parameters have been investigated. The application of our results to the tribology is discussed and the dependence of the static friction force on the system parameters is studied. How to make the material with superlubricity is suggested.

Influence of charging process and size distribution of dust grain on the electric conductivity of dusty plasma

The effects of dust size distribution and charging process of dust grains on the complex electric conductivity of dusty plasmas have been investigated in the present paper. Comparisons are made between real dusty plasma in which there are many different dust grain species and the mono-sized dusty plasma (MDP) in which there is only one kind of dust grain whose size is the average dust size. In some cases the complex electric conductivity of real dusty plasma is larger than that of MDP, while in other cases it is smaller than that of MDP, it depends on the dust size distribution function.

High quality ion acceleration from a double-layer target dominated by the radiation pressure of a transversely Gaussian laser pulse

The ion acceleration from a double-layer target irradiated by a transversely Gaussian laser pulse is investigated by theoretical analysis and particle-in-cell simulations. The main idea of the double-layer target is to match the transverse areal mass density of the target with the laser intensity profile by single ion specie with two densities or by two ion species. Two-dimensional particle-in-cell simulations show that the target deformation and the transverse instability are efficiently suppressed in the double-layer scheme, ions within the laser spot are uniformly accelerated and are well collimated in the forward direction, GeV/u monoenergetic ion beams with very low divergency are observed.

Wakefield effects and solitary waves of an intense short laser pulse propagation in a plasma channel

In the presence of relativistic and channel-coupling nonlinearity and wakefield effects, the propagation characteristics and solitary waves of an intense short laser pulse in a preformed plasma channel are investigated. The evolution equation of the laser spot size is derived by using variational technique, the initial laser and plasma parameters for propagation with constant spot size, periodic defocusing and focusing oscillations, and solitary waves are identified. For illustration, some numerical results are also presented. It is found that the laser focusing is enhanced by the wakefield effects that result in a significant reduced focusing power.

Energy enhancement of proton acceleration in combinational radiation pressure and bubble by optimizing plasma density

The combinational laser radiation pressure and plasma bubble fields to accelerate protons are researched through theoretical analysis and numerical simulations. The dephasing length of the accelerated protons bunch in the front of the bubble and the density gradient effect of background plasma on the accelerating phase are analyzed in detail theoretically. The radiation damping effect on the accelerated protons energy is also considered. And it is demonstrated by two-dimensional particle-in-cell simulations that the protons bunch energy can be increased by using the background plasma with negative density gradient. However, radiation damping makes the maximal energy of the accelerated protons a little reduction.

Bubble core field modification by residual electrons inside the bubble

Bubble core field modification due to the nondepleted electrons present inside the bubble is investigated theoretically. These residual electrons induce charge and current densities that can induce the bubble core field modification as well as the bubble shape change. It is found that the electrons entering into the bubble move backward at almost light speed and would weaken the transverse bubble fields. This reduces the ratio of longitudinal to transverse radius of the bubble. For the longitudinal bubble field, two effects compensate with each other because of their competition between the enhancement by the shortening of bubble shape and the reduction by the residual electrons. Therefore the longitudinal field is hardly changeable. As a comparison we perform particle-in-cell simulations and it is found that the results from theoretical consideration are consistent with simulation results. Implication of the modification of fields on bubble electron acceleration is also discussed briefly.

Electron injection and acceleration in the plasma bubble regime driven by an ultraintense laser pulse combined with using dense-plasma wall and block

An optimizing and alternative scheme for electron injection and acceleration in the wake bubble driven by an ultraintense laser pulse is presented. In this scheme, the dense-plasma wall with an inner diameter matching the expected bubble size is placed along laser propagation direction. Meanwhile, a dense-plasma block dense-plasma is adhered inward transversely at some certain position of the wall. Particle-in-cell simulations are performed, which demonstrate that the block plays an important role in the first electron injection and acceleration. The result shows that a collimated electron bunch with a total number of about 4.04×108μm-1 can be generated and accelerated stably to 1.61 GeV peak energy with 2.6% energy spread. The block contributes about 50% to the accelerated electron injection bunch by tracing and sorting statistically the source.