高能离子在稠密等离子体中的传输和能量沉积

用相对论福克-普朗克方程对高能离子在稠密氘氚等离子体中的碰撞动力学进行了研究,用球谐函数来展开方程的解：格林函数,然后简明地求出了不同能量质子和α粒子在等离子体中的停止时间、减速距离、纵向弥散距离和横向偏转距离.与以前研究离子在等离子体中运动的方法相比,没有假设高能离子在等离子体中损失能量远远小于入射离子能量,求解了纵向弥散距离;并且可以求解横向偏转距离.这些计算对实验上用高能离子加热冷的稠密等离子体,然后进行科学研究具有指导作用,并且可以用来研究快点火的可能性.

Neutron source from thin foil confined by two laser pulses

Neutron production from a thin deuterium-tritium (D-T) foil irradiated by two intense femtosecond laser pulses from opposite sides with zero phase difference is studied analytically and numerically. For the interaction of a laser pulse of amplitude a = 7, focal area 100 mu m(2) and areal density 4.4 x 10(18) cm(-2) with a D-T plasma foil, about 1.17 x 10(21) neutron s(-1) can be obtained, much more than from other methods. The profiles of the ion and electron densities are also calculated.

类氢氖在高温高密度等离子体中的光谱漂移

采用离子球模型，通过自治求解Poisson方程和Dirac方程，得到氖的类氢离子低能级组态的能级能量随等离子体电子温度和电子密度的变化关系，进一步研究了等离子体电子温度和电子密度对光谱漂移的影响。结果表明：光谱漂移随着等离子体电子密度的增大而增大，随着电子温度的升高而减小；谱线精细结构分裂随着电子密度的增大而减小．随着电子温度的升高而增大。等离子体对束缚电子的屏蔽是决定光谱漂移的主要原因。这些变化规律不仅对等离子体光谱模拟结果产生影响，而且使实验上观测光谱的相对或绝对漂移成为可能．从而为高密度等离子体诊断

适用于中等耦合等离子体的碰撞算子

完全电离等离子体中，当试探粒子分布函数fα是关于试探粒子速度vα的偶函数时，导出了一个新的动力学方程的碰撞算子．该碰撞算子同时包括了大角散射（库仑近碰撞）和小角散射（库仑远碰撞）的二体碰撞的贡献，因此，该碰撞算子同时适用于弱耦合（库仑对数ln∧≥10）和中等耦合（库仑对数2≤ln∧≤10）等离子体．而且经过修改的碰撞算子和Rosenbluth势有直接的联系，当试探粒子和场粒子满足条件mα＜mβ（如电子-离子碰撞或Lorentz气体模型）和｜vα｜〉｜vβ｜时，经约化的电子-离子碰撞算子同最初的Fokker

Characterization of a multi-keV x-ray source produced by nanosecond laser irradiation of a solid target: The influence of laser focus spot and target thickness

The influence of focus spot and target thickness on multi-keV x-ray sources generated by 2 ns duration laser heated solid targets are investigated on the Shenguang II laser facility. In the case of thick-foil targets, the experimental data and theoretical analysis show that the emission volume of the x-ray sources is sensitive to the laser focus spot and proportional to the 3 power of the focus spot size. The steady x-ray flux is proportional to the 5/3 power of the focus spot size of the given laser beam in our experimental condition. In the case of thin-foil targets, experimental data show that there is an optimal foil thickness corresponding to the given laser parameters. With the given laser beam, the optimal thin-foil thickness is proportional to the -2/3 power of the focus spot size, and the optimal x-ray energy of thin foil is independent of focus spot size. (C) 2008 American Institute of Physics.

Control of single attosecond pulse generation from the reflection of a synthesized relativistic laser pulse on a solid surface

The influence of the carrier-envelope phase (CEP) of the driving laser pulse on the generation of single attosecond (as) pulses from surface harmonics by using the polarization gating technique is investigated in detail. It is found that the modulation depth of the high-order harmonic spectrum depends on the CEP, and a strong single 68 as pulse can be generated when the CEP is stable and has the proper value. The physical origin of the influence of the CEP is explained in terms of the oscillating mirror model. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2997342]

Acceleration of initially moving electrons by a copropagation intense laser pulse

Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions are imposed, the acceleration of electron by ascending front of laser pulse can be much stronger compared to the deceleration by descending part. Consequently, the electron can obtain significantly high net energy gain. We also report the results of the new scheme that enables a second-step acceleration of electron using laser pulses of peak intensity in the range of 10(19)-10(20) W mu m(2)/cm(2). In the first step the electron acceleration from rest is limited to energies of a few MeV, while in the second step the electron acceleration can be considerably enhanced to about 100 MeV energy.

Generation of periodic ultrashort electron bunches and strongly asymmetric ion Coulomb explosion in nanometer foils interacting with ultra-intense laser pulse

The interaction of a linearly polarized intense laser pulse with an ultrathin nanometer plasma layer is investigated to understand the physics of the ion acceleration. It is shown by the computer simulation that the plasma response to the laser pulse comprises two steps. First, due to the vxB effect, electrons in the plasma layer are extracted and periodic ultrashort relativistic electron bunches are generated every half of a laser period. Second, strongly asymmetric Coulomb explosion of ions in the foil occurs due to the strong electrostatic charge separation, once the foil is burnt through. Followed by the laser accelerated electron bunch, the ion expansion in the forward direction occurs along the laser beam that is much stronger as compared to the backward direction. (c) 2008 American Institute of Physics.

Influence of target thickness on the generation of high-density ion bunches by ultrashort circularly polarized laser pulses

Ion acceleration by ultrashort circularly polarized laser pulse in a solid-density target is investigated using two-dimensional particle-in-cell simulation. The ions are accelerated and compressed by the continuously extending space-charge field created by the evacuation and compression of the target electrons by the laser light pressure. For a sufficiently thin target, the accelerated and compressed ions can reach and exit from the rear surface as a high-density high-energy ion bunch. The peak ion energy depends on the target thickness and reaches maximum when the compressed ion layer can just reach the rear target surface. The compressed ion layer exhibits lateral striation which can be suppressed by using a sharp-rising laser pulse. (c) 2008 American Institute of Physics.

Ion acceleration with mixed solid targets interacting with circularly polarized lasers

The interaction of a circularly polarized laser pulse with a mixed solid target containing two species of ions is studied by particle in cell simulations and analytical model. After the interaction tends to be stable, it is demonstrated that the acceleration is more efficient for the heavier ions than that in plasmas containing a single kind of heavy ion and the acceleration efficiency is higher when its proportion is lower. To obtain monoenergetic heavy-ion beams, a sandwich target with a thin mixed ion layer between two light ion layers and a microstructured target are proposed. The influences of parameters of the laser pulse and target on ion acceleration are discussed in detail. It is found that, when the target is thick enough, a cold target is more appropriate for heavy-ion acceleration than a warm target, and the velocity of the reflected heavy ions is proportional to the laser amplitude.

Guiding and confining fast electrons by transient electric and magnetic fields with a plasma inverse cone

The fast electron propagation in an inverse cone target is investigated computationally and experimentally. Two-dimensional particle-in-cell simulation shows that fast electrons with substantial numbers are generated at the outer tip of an inverse cone target irradiated by a short intense laser pulse. These electrons are guided and confined to propagate along the inverse cone wall, forming a large surface current. The propagation induces strong transient electric and magnetic fields which guide and confine the surface electron current. The experiment qualitatively verifies the guiding and confinement of the strong electron current in the wall surface. The large surface current and induced strong fields are of importance for fast ignition related researches.

Generation of plasma intrinsic oscillation at the front surface of a target irradiated by a circularly polarized laser pulse

In laser-target interaction, the effects of laser intensity on plasma oscillation at the front surface of targets have been investigated by one-dimensional particle in cell simulations. The periodical oscillations of the ion density and electrostatic field at the front surface of the targets are reported for the first time, which is considered as an intrinsic property of the target excited by the laser. The oscillation period depends only on initial plasma density and is irrelevant with laser intensity. Flattop structures with curves in ion phase space are found with a more intense laser pulse due to the larger amplitude variation of the electrostatic field. A simple but valid model is proposed to interpret the curves.

Laser-field synchrotron radiation

An electron with an appropriate initial velocity injected into an oncoming, ultraintense circularly polarized laser pulse can execute a circular relativistic motion at the peak of the laser pulse. The circulating electron then radiates in the same manner as that in the storage ring of a conventional synchrotron source. Owing to the extremely small orbit radius, the laser-field synchrotron radiation thus generated can be a compact source of radiation pulses at short wavelength and short duration.

Electron self-injection and acceleration driven by a tightly focused intense laser beam in an underdense plasma

A scheme for electron self-injection in the laser wakefield acceleration is proposed. In this scheme, the transverse wave breaking of the wakefield and the tightly focused geometry of the laser beam play important roles. A large number of the background electrons are self-injected into the acceleration phase of the wakefield during the defocusing of the tightly focused laser beam as it propagates through an underdense plasma. Particle-in-cell simulations performed using a 2D3V code have shown generation of a collimated electron bunch with a total number of 1.4 x 109 and energies up to 8 MeV. (C) 2005 American Institute of Physics.

Radiation damping effects on the ultrashort x-ray pulses generated by nonlinear Thomson backscattering

Nonlinear Thomson backscattering of an intense Gaussian laser pulse by a counterpropagating energetic electron is investigated by numerically solving the electron equation of motion taking into account the radiative damping force. The backscattered radiation characteristics are different for linearly and circularly polarized lasers because of a difference in their ponderomotive forces acting on the electron. The radiative electron energy loss weakens the backscattered power, breaks the symmetry of the backscattered-pulse profile, and prolongs the duration of the backscattered radiation. With the circularly polarized laser, an adjustable double-peaked backscattered pulse can be obtained. Such a profile has potential applications as a subfemtosecond x-ray pump and probe with adjustable time delay and power ratio. (c) 2006 American Institute of Physics.