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Preferential acceleration of positrons by a filamentation instability between an electron–proton beam and a pair plasma beam 电子-质子束和等离子体束之间的成丝不稳定性对正电子的优先加速
Pub Date : 2020-11-01 DOI: 10.1063/5.0021257
M. Dieckmann, S. Spencer, M. Falk, G. Rowlands
Particle-in-cell (PIC) simulations of collisionless jets of electrons and positrons in an ambient electron-proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. The dominant instability within the jet was a filamentation instability between electrons, protons and positrons. In this work we show that a filamentation instability, between an initially unmagnetized ambient electron-proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that are filled predominantly with particles with the same direction of their electric current vector. Positron filaments are separated by electromagnetic fields from beam electron filaments. Some particles can cross the field boundary and enter the filament of the other species. Positron filaments can neutralize their net charge by collecting the electrons of the ambient plasma while protons cannot easily follow the beam electron filaments. Positron filaments can thus be compressed to a higher density and temperature than the beam electron filaments. Filament mergers, which take place after the exponential growth phase of the instability has ended, lead to an expansion of the beam electron filaments, which amplifies the magnetic field they generate and induces an electric field in this filament. Beam electrons lose a substantial fraction of their kinetic energy to the electric field. Some positrons in the beam electron filament are accelerated by the induced electric field to almost twice their initial speed. The simulations show that a weaker electric field is induced in the positron filament and particles in this filament hardly change their speed.
粒子池(PIC)模拟了电子-质子等离子体中电子和正电子的无碰撞射流,揭示了以电子动能为代价的正电子加速。喷流中主要的不稳定性是电子、质子和正电子之间的细丝不稳定性。在这项工作中,我们展示了在静止的初始未磁化的环境电子-质子等离子体和以非相对论速度穿过它的对等离子体束之间的丝状不稳定性,确实导致了优先的正电子加速。细丝的形成主要由与电流矢量方向相同的粒子填充。正电子丝被电磁场从电子束丝中分离出来。一些粒子可以越过场边界进入其他物种的细丝。正电子丝可以通过收集周围等离子体的电子来中和它们的净电荷,而质子则不容易跟随束流电子丝。因此,正电子细丝可以被压缩到比束流电子细丝更高的密度和温度。在不稳定性的指数增长阶段结束后发生的细丝合并导致电子束细丝的膨胀,从而放大了它们产生的磁场并在细丝中产生电场。束流电子在电场中损失了很大一部分动能。电子束中的一些正电子在感应电场的作用下被加速到其初始速度的两倍。模拟结果表明,在正电子灯丝中产生较弱的电场,灯丝中的粒子几乎没有改变其速度。
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引用次数: 2
A boundary value “reservoir problem” and boundary conditions for multi-moment multifluid simulations of sheaths 护套多矩多流体模拟的边值“储层问题”及边界条件
Pub Date : 2020-10-31 DOI: 10.1063/5.0024510
P. Cagas, A. Hakim, B. Srinivasan
Multifluid simulations of plasma sheaths are increasingly used to model a wide variety of problems in plasma physics ranging from global magnetospheric flows around celestial bodies to plasma-wall interactions in thrusters and fusion devices. For multifluid problems, accurate boundary conditions to model an absorbing wall that resolves a classical sheath remains an open research area. This work justifies the use of vacuum boundary conditions for absorbing walls to show comparable accuracy between a multifluid sheath and lower moments of a continuum-kinetic sheath.
等离子体鞘层的多流体模拟越来越多地用于模拟等离子体物理中的各种问题,从天体周围的全球磁层流动到推进器和聚变装置中的等离子体壁相互作用。对于多流体问题,精确的边界条件来模拟解决经典护套问题的吸收壁仍然是一个开放的研究领域。这项工作证明了真空边界条件用于吸收壁的合理性,以显示多流体护套和连续动力学护套的较低力矩之间的相当精度。
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引用次数: 2
Laser-Accelerated, Low-Divergence 15-MeV Quasimonoenergetic Electron Bunches at 1 kHz 激光加速,低发散15兆电子伏特准单能电子束在1千赫
Pub Date : 2020-10-29 DOI: 10.1103/PhysRevX.11.021055
F. Salehi, M. Le, L. Railing, M. Kolesik, H. Milchberg
We demonstrate laser wakefield acceleration of quasi-monoenergetic electron bunches up to 15 MeV at 1 kHz repetition rate with 2.5 pC charge per bunch and a core with < 7 mrad beam divergence. Acceleration is driven by 5 fs, < 2.7 mJ laser pulses incident on a thin, near-critical density hydrogen gas jet. Low beam divergence is attributed to reduced sensitivity to laser carrier envelope phase slip, achieved in two ways using laser polarization and gas jet control: (1) electron injection into the wake on the gas jet's plasma density downramp, and (2) use of circularly polarized drive pulses. Under conditions of mild wavebreaking in the downramp, electron beam profiles have a 2D Lorentzian shape consistent with a kappa electron energy distribution. Such distributions had previously been observed only in space or dusty plasmas. We attribute this shape to the strongly correlated collisionless bunch confined by the quadratic wakefield bubble potential, where transverse velocity space diffusion is imparted to the bunch by the red-shifted laser field in the bubble.
我们证明了激光尾迹场加速准单能电子束高达15 MeV,重复频率为1 kHz,每束2.5 pC电荷,核心束发散小于7 mrad。加速是由5fs,小于2.7 mJ的激光脉冲入射到薄的,接近临界密度的氢气射流上。光束散度低的原因是对激光载流子包络相滑移的敏感性降低,这可以通过激光偏振和气体射流控制两种方式实现:(1)在气体射流的等离子体密度下降时向尾迹注入电子,(2)使用圆极化驱动脉冲。在下坡轻微破波的条件下,电子束分布具有符合kappa电子能量分布的二维洛伦兹形状。这种分布以前只在太空或尘埃等离子体中观察到。我们将这种形状归因于受二次尾场泡势限制的强相关无碰撞束,其中泡中的红移激光场将横向速度空间扩散传递给束。
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引用次数: 18
Thermomagnetic instability of plasma composition gradients 等离子体组成梯度的热磁不稳定性
Pub Date : 2020-10-28 DOI: 10.1063/5.0027210
J. Sadler, Hui Li
We show that, under Braginskii magneto-hydrodynamics, anti-parallel gradients in average ion charge state and electron temperature can be unstable to the growth of self-generated magnetic fields. The instability is analogous to the field-generating thermomagnetic instability, although it is driven by the collisional thermal force magnetic source term rather than the Biermann battery term. The gradient in ion charge state causes a gradient in collisionality, which couples with temperature perturbations to create a self-generated magnetic field. This magnetic field deflects the electron heat flux in a way that reinforces the temperature perturbation. The derived linearized growth rate, typically on hydrodynamic timescales, includes the resistive and thermal smoothing. It increases with large ion composition gradients and electron heat flux, conditions typical of the hohlraum walls or contaminant mix jets in inertial confinement fusion implosions. However, extended magneto-hydrodynamic simulations indicate that the instability is usually dominated and stabilized by the nonlinear Nernst advection, in a similar manner to the standard thermomagnetic instability.
研究表明,在Braginskii磁流体力学条件下,离子平均电荷态和电子温度的反平行梯度对自生磁场的生长是不稳定的。这种不稳定性类似于产生磁场的热磁不稳定性,尽管它是由碰撞热力磁源项而不是比尔曼电池项驱动的。离子电荷态的梯度引起碰撞的梯度,与温度扰动耦合产生自生磁场。这个磁场以一种强化温度扰动的方式使电子热流偏转。导出的线性化增长率,通常在水动力时间尺度上,包括电阻和热平滑。随着离子组成梯度和电子热流的增大,惯性约束聚变内爆中典型的热腔壁或污染物混合射流的情况下,它会增加。然而,扩展的磁流体动力学模拟表明,与标准的热磁不稳定性类似,非线性能斯特平流通常是不稳定性的主导和稳定因素。
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引用次数: 1
Numerical scheme for evaluating the collision integrals for triple interactions in relativistic plasma 计算相对论等离子体中三重相互作用碰撞积分的数值格式
Pub Date : 2020-10-27 DOI: 10.1063/5.0022931
M. Prakapenia, I. Siutsou, G. Vereshchagin
Binary interactions in relativistic plasma, such as Coulomb and Compton scattering as well as pair creation and annihilation are well known and studied in details. Triple interactions, namely relativistic bremsstrahlung, double Compton scattering, radiative pair production, triple pair production/annihilation and their inverse processes, are usually considered as emission processes in astrophysical problems, as well as in laboratory plasmas. Their role in plasma kinetics is fundamental [1]. We present a new conservative scheme for computation of Uehling-Uhlenbeck collision integral for all triple interactions in relativistic plasma based on direct integration of exact QED matrix elements. Reaction rates for thermal distributions are compared, where possible, with the corresponding analytic expressions, showing good agreement. Our results are relevant for quantitative description of relativistic plasmas out of equilibrium, both in astrophysical and laboratory conditions.
相对论等离子体中的二元相互作用,如库仑散射和康普顿散射,以及对产生和湮灭都是众所周知的,并进行了详细的研究。三重相互作用,即相对论轫致辐射、双康普顿散射、辐射对产生、三对产生/湮灭及其逆过程,通常被认为是天体物理问题和实验室等离子体中的发射过程。它们在等离子体动力学中的作用是基础性的。基于精确QED矩阵元素的直接积分,给出了计算相对论等离子体中所有三重相互作用的Uehling-Uhlenbeck碰撞积分的一种新的保守格式。在可能的情况下,将热分布的反应速率与相应的解析表达式进行比较,结果一致。我们的结果与天体物理和实验室条件下相对论性等离子体失去平衡的定量描述有关。
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引用次数: 2
Hydrodynamical model of QED cascade expansion in an extremely strong laser pulse 超强激光脉冲中QED级联膨胀的流体动力学模型
Pub Date : 2020-10-27 DOI: 10.1063/5.0035347
A. S. Samsonov, I. Kostyukov, E. Nerush
Development of the self-sustained quantum-electrodynamical (QED) cascade in a single strong laser pulse is studied analytically and numerically. The hydrodynamical approach is used to construct the analytical model of the cascade evolution, which includes the key features of the cascade observed in 3D QED particle-in-cell (QED-PIC) simulations such as the magnetic field predominance in the cascade plasma and laser energy absorption. The equations of the model are derived in the closed form and are solved numerically. Direct comparison between the solutions of the model equations and 3D QED-PIC simulations shows that our model is able to describe the complex nonlinear process of the cascade development qualitatively well. The various regimes of the interaction based on the intensity of the laser pulse are revealed in both the solutions of the model equations and the results of the QED-PIC simulations.
本文对单强激光脉冲中自持续量子-电动力学(QED)级联的发展进行了分析和数值研究。采用流体动力学方法建立了级联演化的解析模型,该模型包含了三维QED粒子池(QED- pic)模拟中观察到的级联的关键特征,如级联等离子体中的磁场优势和激光能量吸收。该模型的方程以封闭形式导出,并进行了数值求解。将模型方程解与三维QED-PIC模拟结果直接比较,表明该模型能够较好地定性描述复杂的非线性叶栅发展过程。在模型方程的解和QED-PIC模拟结果中揭示了基于激光脉冲强度的相互作用的各种形式。
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引用次数: 4
Reaching high laser intensity by a radiating electron 通过辐射电子达到高激光强度的
Pub Date : 2020-10-21 DOI: 10.1103/PhysRevA.103.053114
M. Jirka, P. Sasorov, S. Bulanov, G. Korn, B. Rus, S. V. Bulanov
Interaction of an electron with the counter-propagating electromagnetic wave is studied theoretically and with the particle-in-cell simulations in the regime of quantum radiation reaction. We find the electron energy in the center of the laser pulse, as it is a key factor for testing the non-linear quantum electrodynamics vacuum properties in the laser-electron collision in the regime of multi-photon Compton scattering and vacuum Cherenkov radiation. With multiparametric analysis we provide the conditions on electron initial energy for reaching the center of the laser pulse and emitting Cherenkov photons.
从理论上研究了电子与反传播电磁波的相互作用,并在量子辐射反应机制下进行了粒子胞内模拟。在多光子康普顿散射和真空切伦科夫辐射下,激光-电子碰撞的非线性量子电动力学真空特性测试的关键因素是激光脉冲中心的电子能量。通过多参数分析,给出了电子到达激光脉冲中心并发射切伦科夫光子的初始能量条件。
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引用次数: 2
Topology of the warm plasma dispersion relation at the second harmonic electron cyclotron resonance layer 二次谐波电子回旋共振层热等离子体色散关系的拓扑结构
Pub Date : 2020-10-16 DOI: 10.1063/5.0033880
P. L. Joostens, E. Westerhof
The Warm Plasma Dispersion Relation, for waves in the electron cyclotron resonance range of frequencies, can be cast into the form of a bi-quadratic equation for $N_perp$, where the coefficients are a function of $N_perp^2$ and an iterative procedure is required to obtain a solution. However, this iterative procedure is not well understood and fails to converge towards a solution at the second harmonic resonance layer. In particular at higher densities where the wave can couple to an electron Bernstein wave. This paper focuses on a solution to the poor convergence of the iterative method, enabling determination of the topology of the dispersion relation around the second harmonic using a fully relativistic code for oblique waves. A feed-forward controller is proposed with the ability to adjust the rotation of a step of $N_perp^2$ within the complex plane, while also limiting the step-size. It is shown that implementation of the controller stabilizes unstable solutions, while improving overall robustness of the iteration. This allows the evaluation of the coupling between the fast extraordinary mode and electron Bernstein waves at the second harmonic electron cyclotron resonance layer, for non-perpendicularly propagating waves.
对于电子回旋共振频率范围内的波,热等离子体色散关系可以转化为双二次方程的形式,其中系数是N_perp^2$的函数,需要迭代过程才能得到解。然而,这种迭代过程不是很好地理解,并且不能收敛到第二谐波共振层的解。特别是在更高的密度,波可以耦合到一个电子伯恩斯坦波。本文着重解决了迭代法收敛性差的问题,利用斜波的完全相对论编码确定了二次谐波周围色散关系的拓扑结构。提出了一种前馈控制器,该控制器能够在复平面内调整$N_perp^2$步长的旋转,同时也限制了步长。结果表明,该控制器的实现稳定了不稳定解,同时提高了迭代的整体鲁棒性。这允许对非垂直传播波在二次谐波电子回旋共振层上的快速异常模式和电子伯恩斯坦波之间的耦合进行评估。
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引用次数: 0
Exact hybrid-kinetic equilibria for magnetized plasmas with shearing flows 剪切流磁化等离子体的精确混合动力学平衡
Pub Date : 2020-10-14 DOI: 10.1051/0004-6361/202039656
G. Guzzi, A. Settino, F. Valentini, F. Malara
Context. Magnetized plasmas characterized by shearing flows are present in many natural contexts, such as the Earth's magnetopause and the solar wind. The collisionless nature of involved plasmas requires a kinetic description. When the width of the shear layer is of the order of ion scales, the Hybrid Vlasov-Maxwell approach can be adopted. Aims. The aim of the paper is to derive explicit forms for stationary configurations of magnetized plasmas with planar shearing flows,within the Hybrid Vlasov-Maxwell description. Two configurations are considered: the first with a uniform magnetic field obliquely directed with respect to the bulk velocity; and the second with a uniform-magnitude variable-direction magnetic field. Methods. Stationary ion distribution functions are obtained by combining single-particle constant of motions, which are derived studying particle dynamics. Preliminary information about the form of the distribution functions are analytically derived considering a local approximation for the background electromagnetic field. Then, a numerical method is set up to obtain a solution for general profiles. Results. The explicit distribution functions that are found allow to obtain profiles of density, bulk velocity, temperature and heat flux. Anisotropy and agyrotropy in the distribution function are also evaluated. Stationarity of the solution during numerical simulations is checked in the uniform oblique magnetic field case. Conclusions. The considered configurations can be used as models for the Earth's magnetopause in simulations of the Kelvin-Helmholtz instability.
上下文。以剪切流为特征的磁化等离子体存在于许多自然环境中,例如地球的磁层顶和太阳风。有关等离子体的无碰撞特性需要动力学描述。当剪切层宽度为离子尺度数量级时,可采用混合Vlasov-Maxwell方法。目标本文的目的是推导出具有平面剪切流的磁化等离子体的固定构型的显式形式,在混合Vlasov-Maxwell描述中。考虑了两种结构:第一种是均匀的磁场,斜向体速度;第二种是等量级可变方向磁场。方法。结合研究粒子动力学导出的单粒子运动常数,得到了平稳离子分布函数。考虑背景电磁场的局部近似,对分布函数形式的初步信息进行了解析推导。然后,建立了一种求解一般剖面的数值方法。结果。所发现的显式分布函数允许得到密度、体速度、温度和热流密度的分布。并对分布函数的各向异性和各向异性进行了评价。在均匀斜磁场情况下,验证了数值模拟过程中解的平稳性。结论。所考虑的结构可以用作模拟开尔文-亥姆霍兹不稳定性时地球磁层顶的模型。
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引用次数: 1
Non destructive testing of actively cooled plasma facing components by means of thermal transient excitation and infrared imaging. 热瞬态激发和红外成像技术在主动冷却等离子体表面构件无损检测中的应用。
Pub Date : 2020-10-06 DOI: 10.1016/B978-0-444-82762-3.50081-1
R. Mitteau, S. Berrebi, P. Chappuis, Ph. Darses, A. Dufayet, L. Garampon, D. Guilhem, M. Lipa, V. Martin, H. Roche
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引用次数: 14
期刊
arXiv: Plasma Physics
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