Magneto‐Modulational Instability in Relativistic Plasmas

The behavior of magnetic fields generated by high frequency transverse plasmons in relativistic plasmas can be described by a set of nonlinear coupling equations, which has considered the nonlinear wave–wave, wave– particle interactions and the relativistic effects of electrons. Modulational instability of the spontaneous magnetic fields is investigated on the basis of the nonlinear coupling equations. Analytical and numerical results indicate the self‐generated magnetic fields are modulationally unstable and will be localized in a narrow region. The characteristic scale and maximum growth rate of the magnetic fields depend on the average Lorentz factor of electrons and the energy density of transverse plasmons. The relativistic effects of electrons will enhance the self‐focusing of magnetic fields (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

飞秒强激光作用下线性等离子体层中光场和电子密度的自洽分布

自洽求解了圆偏振的飞秒强激光作用下线性等离子体层中光场和电子密度的分布.研究发现在激光有质动力的作用下，电子密度分布严重偏离离子密度分布，甚至出现了一系列的“电子岛”和“电子空腔”.由于电荷分离，等离子体内形成了很强的静电场，一部分激光能量转化为等离子体内的静电能.线性等离子体层储存静电能的大小随着入射激光强度的增加而显著上升. 关键词： 飞秒激光 相对论等离子体 电子密度 有质动力     

激光与相对论电子束相互作用中阿秒X射线脉冲的产生

本文对激光与相对论电子束相互作用产生的阿秒X射线脉冲进行了研究.阿秒X射线脉冲是由于激光被相对论运动的电子束经过汤姆孙后向散射产生的.讨论了等离子体参数对产生的阿秒X射线的影响.发现其波长随着入射激光的频率的增加或电子束的速度增加而减小.选择合适的参数还可以获得"水窗"波段的X射线.还讨论了相对论电子束的密度与其前沿的密度梯度的大小对所产生X射线的转化效率的影响. 关键词： 阿秒X射线脉冲 汤姆孙后向散射 超强激光 相对论电子束     

A New Scheme for High‐Intensity Laser‐Driven Electron Acceleration in a Plasma

We propose a new approach to high‐intensity relativistic laser‐driven electron acceleration in a plasma. Here, we demonstrate that a plasma wave generated by a stimulated forward‐scattering of an incident laser pulse can be in the longest acceleration phase with injected relativistic beam electrons. This is why the plasma wave has the maximum amplification coefficient which is determined by the acceleration time and the breakdown (overturn) electric field in which the acceleration of the injected beam electrons occurs. We must note that for the longest acceleration phase the relativity of the injected beam electrons plays a crucial role in our scheme. We estimate qualitatively the acceleration parameters of relativistic electrons in the field of a plasma wave generated at the stimulated forward‐scattering of a high‐intensity laser pulse in a plasma. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

相对论质量修正效应对超高次谐波的影响

通过分别求解含时狄拉克方程和含时薛定谔方程, 研究了一维模型原子在相对论超强激光脉冲作用下的超高次谐波发射过程. 研究结果表明: 在弱场强条件下, 相对论的模拟结果可以退化到非相对论的结果; 随着场强的增强, 可以逐渐观察到明显的相对论质量修正效应. 此外, 根据发展的相对论的"三步"模型并结合小波时频分析方法, 分析了谐波平台的截止位置和发射效率.     

Laser-driven collisions of electron bunches

A novel scheme allowing for relativistic collisions of laser-accelerated electrons is introduced. Two spatially separated electron bunches are driven in opposite directions by two counterpropagating laser pulses until they reach the point of collision which lies within the laser fields. This method can be employed to accelerate electrons to the maximum kinetic energy which can be transferred to charged particles by plane propagating laser fields. Due to the symmetric setup, the center of momentum is at rest with respect to the laser propagation direction such that virtually the whole kinetic energy is available for particle reactions.     

Intense short-pulse lasers irradiating wire and hollow plasma fibers

When an intense laser pulse irradiates a solid-density foil target, electrons produced at the relativistic critical density can be accelerated to relativistic energy by the ponderomotive force. When a plasma fiber is attached to the back of the foil, the produced relativistic electrons are guided to propagate along the fiber for a long distance, because the high-current electron beam induces strong radial electric fields in the fiber. Transport and heating of intense laser-driven relativistic electrons in both wire and hollow plasma fibers are compared theoretically and numerically. We found that the coupling efficiency from the laser to the plasma fiber depends on the fiber structure. Because of the enhanced return currents in the wire fiber, the temperature in the wire fiber is higher than that in the hollow fiber.     

Laser-driven recollisions generalized to relativistic energies

The important process of laser-driven recollisions, where electrons are accelerated by strong laser fields and return to their parent ions, breaks down if the laser intensities imply relativistic electron dynamics. In this case, the Lorentz force drags the electrons away in the laser propagation direction, which inhibits recollisions. Here, a variety of schemes are discussed and compared which generalize the concept of recollisions to the relativistic regime. Additional static electric fields, antisymmetric initial states, and tailored laser pulses are suitable for weakly to moderately relativistic energies, whereas standing waves, preaccelerated ions, positronium, and counterpropagating consecutive pulses allow for recollisions up to the highly relativistic regime.     

超相对论强度激光与薄膜靶作用中0.4 nm以下X射线阿秒脉冲的产生

用一维粒子模拟程序对功率密度在10²² W/cm²以上的超强激光驱动薄膜靶产生的相对论电子层及其经过汤姆孙散射产生的阿秒X射线进行了研究. 结果表明, 在超相对论强度范围下增大驱动激光强度, 相应减小等离子体密度及厚度可使电子层获得更高纵向动量, 使汤姆孙散射光明显向更短波长移动. 优化相关参数得到了波长为 1.168 nm的阿秒脉冲. 经过对倍频探测光方案与驱动光以及薄膜靶参数进行综合考虑和优化, 得到的X射线相干辐射波长有效减小到0.4 nm以下, 产生的光子能量达到2 keV以上. 关键词： 超相对论强度激光 阿秒X射线 相对论电子层 汤姆孙后向散射     

Heating mechanisms in short-pulse laser-driven cone targets

The fast ignitor is a modern approach to laser fusion that uses a short-pulse laser to initiate thermonuclear burn. In its simplest form the laser launches relativistic electrons that carry its energy to a precompressed fusion target. Cones have been used to give the light access to the dense target core through the low-density ablative cloud surrounding it. Here the ANTHEM implicit hybrid simulation model shows that the peak ion temperatures measured in recent cone target experiments arose chiefly from return current joule heating, mildly supplemented by relativistic electron drag. Magnetic fields augment this heating only slightly, but capture hot electrons near the cone surface and force the hot electron stream into filaments.     

Characterization of relativistic electrons generated by a cone guiding laser pulse

We demonstrated the interaction of a gold cone target with a femto second(fs) laser pulse above the relativistic intensity of 1.37×10 18 μm 2 W/cm 2.Relativistic electrons with energy above 2 MeV were observed.A 25%-40% increase of the electron temperature is achieved compared to the case when a plane gold target is used.The electron temperature increase results from the guiding of the laser beam at the tip and the intense quasistatic magnetic field in the cone geometry.The behavior of the relativistic electrons is verified in our 2D-PIC simulations.     

Additional acceleration and collimation of relativistic electron beams by magnetic field resonance at very high intensity laser interaction

For the interpretation of experiments for acceleration of electrons at interaction up to nearly GeV energy in laser produced plasmas, we present a new model using interaction magnetic fields. In addition to the ponderomotive acceleration of highly relativistic electrons at the interaction of very short and very intense laser pulses, a further acceleration is derived from the interaction of these electron beams with the spontaneous magnetic fields of about 100 MG. This additional acceleration is the result of a laser-magnetic resonance acceleration (LMRA) around the peak of the azimuthal magnetic field. This causes the electrons to gain energy within a laser period. Using a Gaussian laser pulse, the LMRA acceleration of the electrons depends on the laser polarization. Since this is in the resonance regime, the strong magnetic fields affect the electron acceleration considerably. The mechanism results in good collimated high energetic electrons propagating along the center axis of the laser beam as has been observed by experiments and is reproduced by our numerical simulations. PACS 41.75.Jv; 52.38.Kd; 52.65.Cc     

Obliquely propagating quantum solitary waves in quantum‐magnetized plasma with ultra‐relativistic degenerate electrons and positrons

The oblique propagation of the quantum electrostatic solitary waves in magnetized relativistic quantum plasma is investigated using the quantum hydrodynamic equations. The plasma consists of dynamic relativistic degenerate electrons and positrons and a weakly relativistic ion beam. The Zakharov‐Kuznetsov equation is derived using the standard reductive perturbation technique that admits an obliquely propagating soliton solution. It is found that two types of quantum acoustic modes, that is, a slow acoustic mode and fast acoustic mode, could be propagated in our plasma model. The parameter that determines the nature of soliton, that is, compressive or rarefactive soliton, for slow mode is investigated. Our numerical results show that for the slow mode, the determining parameter is ion beam velocity in the case of relativistic degenerate electrons. We also have examined the effects of plasma parameters (like the beam velocity, the density ratio of positron to electron, the relativistic factor, and the propagation angle) on the characteristics of solitary waves.     

相对论电子探测谱仪的设计及标定

考虑电子的相对论效应,根据电磁学理论和相对论公式建立了电子磁谱仪的原理;按照该原理设计了电子的磁谱仪,用补偿磁路改善了磁场的均匀性;按照磁谱仪的结构对其进行了测试和标定;以LiF热释光探测器作为记录元件,可获得相对论电子的能量分布。实验上典型的测量结果与国外计算机模拟的结果较好地一致,从而证明电子磁谱仪的可靠性。     

Ion acceleration regimes in underdense plasmas

Acceleration of large populations of ions up to high (relativistic) energies may represent one of the most important and interesting tools that can be provided by the interaction of petawatt laser pulses with matter. In this paper, the basic mechanisms of ion acceleration by short laser pulses are studied in underdense plasmas. The ion acceleration does not originate directly from the pulse fields, but it is mediated by the electrons in the form of electrostatic fields originating from channeling, double layer formation and Coulomb explosion     

超短脉冲激光与稀薄等离子体相互作用的准静态粒子模拟研究

具体讨论准静态近似在粒子模拟技术中的实现方法，主要包括：简化物理模型的建立，数值模拟方法的实现，程序结构的建立.最后，给出了三个成功的数值模拟结果，短脉冲激光的自聚焦现象、激光尾流场的激发和自生磁场现象，并进行了物理分析. 关键词： 准静态 粒子模拟 激光尾流场 自聚焦     

Ion response to relativistic electron bunches in the blowout regime of laser-plasma accelerators

The ion response to relativistic electron bunches in the so called bubble or blowout regime of a laser-plasma accelerator is discussed. In response to the strong fields of the accelerated electrons the ions form a central filament along the laser axis that can be compressed to densities 2 orders of magnitude higher than the initial particle density. A theory of the filament formation and a model of ion self-compression are proposed. It is also shown that in the case of a sharp rear plasma-vacuum interface the ions can be accelerated by a combination of three basic mechanisms. The long time ion evolution that results from the strong electrostatic fields of an electron bunch provides a unique diagnostic of laser-plasma accelerators.     

电子在激光驻波场中运动产生的太赫兹及X射线辐射研究

采用单电子模型和经典辐射理论分别对低能和高能电子在线偏振激光驻波场中的运动和辐射过程进行了研究. 结果表明: 垂直于激光电场方向入射的低速电子在激光驻波场中随着光强的增大, 逐渐从一维近周期运动演变为二维折叠运动, 并产生强的微米量级波长的太赫兹辐射; 高能电子垂直或者平行于激光电场方向入射到激光驻波场中, 都会产生波长在几个纳米的高频辐射; 低能电子与激光驻波场作用中, 激光强度影响着电子的运动形式、辐射频率以及辐射强度; 高能电子入射时, 激光强度影响了电子高频辐射的强度, 电子初始能量影响着辐射的频率; 电子能量越高, 产生的辐射频率越大. 研究表明可以由激光加速电子的方式得到不同能量的电子束, 并利用电子束在激光驻波场的辐射使之成为太赫兹和X射线波段的小型辐射源. 研究结果可以为实验研究和利用激光驻波场中的电子辐射提供依据.