朗缪尔波中电子俘获非线性的阈值
Threshold for Electron Trapping Nonlinearity in Langmuir Waves
摘要：
我们评估时，电子捕获非线性预期是重要的朗缪尔波。其基本判据是：在速度空间的俘获区，电子的退陷速率nu_d的倒数必须超过深陷电子的反弹周期τ_B =（n_e/delta n）^{1/2} 2 π/omega_pe。无单位品质因数，“反弹数”N_B = 1/（nu_d tau_B），封装了该条件并定义了N_B=1的捕获阈值幅度。发现对流损失（横向和纵向）的空间有限的朗缪尔波的脱陷率。利用2D-2 V Vlasov程序Loki对有限横截面的驱动波进行了数值模拟，结果表明，对于横向损耗，俘获非线性随N_B的增加而增加，并且在N_B ~ 1时，俘获非线性显著增加。由于库仑碰撞（电子-电子和电子-离子）的脱陷率也被发现，与俯仰角散射和平行的阻力和扩散处理在一个统一的方式。给出了一种结合对流和碰撞去陷的简单方法。介绍了在惯性约束聚变靶中低密度等离子体条件下的应用。结果表明，对流横向损耗通常是单个f/8激光散斑中最有效的退陷过程。对于典型的等离子体和激光条件下的内激光锥的国家点火装置，局部反射率约3%的估计产生显着的捕获效果。
英文摘要：
We assess when electron trapping nonlinearity is expected to be important in Langmuir waves. The basic criterion is that the inverse of the detrapping rate nu_d of electrons in the trapping region of velocity space must exceed the bounce period of deeply-trapped electrons, tau_B = (n_e/delta n)^{1/2} 2pi/omega_pe. A unitless figure of merit, the "bounce number" N_B = 1/(nu_d tau_B), encapsulates this condition and defines a trapping threshold amplitude for which N_B=1. The detrapping rate is found for convective loss (transverse and longitudinal) out of a spatially finite Langmuir wave. Simulations of driven waves with a finite transverse profile, using the 2D-2V Vlasov code Loki, show trapping nonlinearity increases continuously with N_B for transverse loss, and is significant for N_B ~ 1. The detrapping rate due to Coulomb collisions (both electron-electron and electron-ion) is also found, with pitch-angle scattering and parallel drag and diffusion treated in a unified manner. A simple way to combine convective and collisional detrapping is given. Application to underdense plasma conditions in inertial confinement fusion targets is presented. The results show that convective transverse loss is usually the most potent detrapping process in a single f/8 laser speckle. For typical plasma and laser conditions on the inner laser cones of the National Ignition Facility, local reflectivities ~3% are estimated to produce significant trapping effects.
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