非均匀等离子体对强激光传播及电子束输运的影响

doi:10.19596/j.cnki.1001-246x.8622

摘要/Abstract

摘要：

本文介绍近期针对非均匀等离子体对强激光传播和电子束输运影响取得的研究进展, 首先研究弱无序分布等离子体对强激光传播的影响, 提出强激光在弱无序等离子体中存在非线性分支流传输机制, 并阐明光电离效应及相对论效应对分支流的重要影响。此外, 研究等离子体密度梯度对相对论电子束输运过程的影响, 发现相对论电子束输运所激发的静电波在空间固定点处的波数或相速度随时间变化, 并且不依赖于等离子体密度的上升或下降, 静电波的局域空间波数最终随时间逐渐增大, 这导致在非均匀等离子体中静电波通过朗道阻尼方式将能量耗散转移给背景电子, 表现为一种由背景等离子体密度梯度引起的束流能量耗散新机制。

关键词: 非均匀等离子体, 强激光, 相对论电子束, 分支流, 朗道阻尼

Abstract:

This work introduces our recent research works on the propagation of intense laser and transport of relativistic electron beam in inhomogeneous plasmas. First of all, we investigated the propagation of intense laser pulse in plasma with randomly uneven density distribution and found a new nonlinear branched flow regime of intense laser propagation in inhomogeneous plasma. In particular, we identify the important effects played by the laser photoionization and relativistic motion of electrons. In addition, we also investigated the plasma density gradient effect on evolution of electrostatic wave excited by ultra-relativistic electron beam in inhomogeneous plasma. It is found that the local region wavenumber and phase velocity of the excited wave varies with time because of the plasma inhomogeneity. Independent of the positive and negative density gradient, the wavenumber finally increases with time. As a result, Landau damping gradually becomes dominant in the whole region of inhomogeneous plasma, and leads to transfer of the wave energy to background plasma electrons, presenting a novel energy dissipation regime caused by the plasma density gradient.

Key words: inhomogeneous plasma, intense laser, relativistic electron beam, branched flow, Landau damping

黄太武, 蒋轲, 李然, 周沧涛. 非均匀等离子体对强激光传播及电子束输运的影响[J]. 计算物理, 2023, 40(2): 147-158.

Taiwu HUANG, Ke JIANG, Ran LI, Cangtao ZHOU. Propagation of Intense Laser and Transport of Relativistic Electron Beam in Inhomogeneous Plasmas[J]. Chinese Journal of Computational Physics, 2023, 40(2): 147-158.

图/表 6

图1 (a) 初始电子密度空间分布ne/nc；(b) 相应的等离子体折射率η空间分布

Fig.1 Initial distributions of (a) electron density ne/nc and (b) plasma refractive index η

图2 (a)~(d) 激光强度空间分布I/(W·cm-2)；(c)~(h) 电子密度空间分布ne/nc；(i)~(l) 等离子体折射率η空间分布(从左至右I = 1014, 1016, 1018, 1020W·cm-2。)

Fig.2 Distributions of (a)~(d) laser intensity I/W·cm-2; (c)~(h) electron density ne/nc and (i)~(l) plasma refractive index η (From left to right, I = 1014, 1016, 1018, 1020 W·cm-2.)

图3 首个焦散面与源之间的距离d0与激光强度I的依赖关系

Fig.3 The distance from the source to the first caustics d0 for different laser intensities

图4 相对论电子束在等离子体(情形A和情形B)中输运时激发的静电波场(非均匀等离子体区域(区域Ⅱ)为100 μm~790 μm。)(a)~(b) t = 3 500 fs时刻(红线为情形B，蓝线为情形A)的静电波场; (c) 情形A中，x = 50 μm (品红线，位于区域Ⅰ)以及x = 900 μm(蓝线，位于区域Ⅲ)处电场随时间的变化; (d) 850 μm~950 μm非均匀区域内，情形B(红线)以及情形A(蓝线)的电场分布，所示时刻为t = 3 500 fs; (e) 情形A中，x = 270 μm(红线)、x = 445 μm(绿线)、以及x = 820 μm(蓝线)处电场随时间的变化

Fig.4 Electrostatic wave field excited by relativistic electron beam transport in background plasma in Cases A and B, where inhomogeneous plasma is distributed in the region of 100 μm~790 μm (a)~(b) electrostatic wave field for Case B (the red line) and Case A (the blue line) at t = 3 500 fs; (c) temporal evolution of the electric field at positions of x = 50 μm (the magenta line) and x = 900 μm (the blue line) in Case A; (d) electric field in the region of 850 μm~950 μm at t = 3 500 fs, where the red line represents the Case B and the blue one represents Case A; (e) temporal evolution of the electric field at positions of x = 270 μm (red line), x = 445 μm (green line), and x = 820 μm (blue line) in Case A

图5 (a) 情形B中300 ~ 550 μm区域内，t = 1 840 fs(红色实线)、t = 3 600 fs(绿色实线)以及t = 5 400 fs (蓝色虚线)时刻的静电波场分布; (b) 情形A中400 ~ 450 μm区域内，t = 1 840 fs(红色实线)以及t = 5 400 fs(蓝色虚线)时刻的静电波场分布

Fig.5 (a) Electrostatic wave field in the region of 300 ~ 550 μm for Case B at different time moments of t = 1 840 fs (red-solid line), t = 3 600 fs (green-solid line), and t = 5 400 fs (blue-dotted line); (b) electrostatic wave field in the region of 400 ~ 450 μm for Case A at different time moments of t = 1 840 fs (red-solid line) and t = 5 400 fs (blue-dotted line)

图6 (a) t ≈ 830 fs，情形C中50~250 μm区域内的静电波场分布; (b)~(d) 130~140 μm区域内，t ≈ 830 fs(红线)、t ≈ 2 800 fs(绿线)以及t ≈ 5 000 fs(蓝线)时刻的静电波场分布(在情形C中，非均匀等离子体分布在100~169 μm的区域。)

Fig.6 (a) Electrostatic wave field in 50~250 μm region for Case C at t ≈ 830 fs; (b)~(d) electrostatic wave field in 130~140 μm region at time moments of t ≈ 830 fs (red line), t ≈ 2 800 fs (green line), and t ≈ 5 000 fs (blue line) (In Case C, the inhomogeneous plasma is distributed in 100~169 μm.)

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