Sherlock M, Michel P, Strozzi D J, Divol L, Kur E, Zimmerman G
Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
Phys Rev E. 2024 May;109(5-2):055201. doi: 10.1103/PhysRevE.109.055201.
We provide analytic expressions for the effective Coulomb logarithm for inverse bremsstrahlung absorption which predict significant corrections to the Langdon effect and overall absorption rate compared to previous estimates. The calculation of the collisional absorption rate of laser energy in a plasma by the inverse bremsstrahlung mechanism usually makes the approximation of a constant Coulomb logarithm. We dispense with this approximation and instead take into account the velocity dependence of the Coulomb logarithm, leading to a more accurate expression for the absorption rate valid in both classical and quantum conditions. In contrast to previous work, the laser intensity enters into the Coulomb logarithm. In most laser-plasma interactions the electron distribution function is super-Gaussian [Langdon, Phys. Rev. Lett. 44, 575 (1980)0031-900710.1103/PhysRevLett.44.575], and we find the absorption rate under these conditions is increased by as much as ≈30% compared to previous estimates at low density. In many cases of interest the correction to Langdon's predicted reduction in absorption is large; for example at Z=6 and T_{e}=400eV the Langdon prediction for the absorption is in error by a factor of ≈2. However, we also account for the additional effect of plasma screening, which predicts a reduction in absorption by a similar amount (up to ≈30%). These two effects compete to determine the overall absorption, which may be increased or decreased, depending on the conditions. The corrections can be incorporated into radiation-hydrodynamics simulation codes by replacing the familiar Coulomb logarithm with an analytic expression which depends on the super-Gaussian order "M" and the screening length.
我们给出了轫致辐射逆吸收有效库仑对数的解析表达式，与先前的估计相比，该表达式对朗登效应和整体吸收率有显著修正。通过轫致辐射机制计算等离子体中激光能量的碰撞吸收率时，通常会采用库仑对数为常数的近似。我们摒弃了这一近似，转而考虑库仑对数的速度依赖性，从而得到在经典和量子条件下均有效的更精确的吸收率表达式。与先前的工作不同，激光强度进入了库仑对数。在大多数激光 - 等离子体相互作用中，电子分布函数是超高斯分布[朗登，《物理评论快报》44, 575 (1980)0031 - 900710.1103/PhysRevLett.44.575]，我们发现与低密度下先前的估计相比，在这些条件下吸收率提高了约30%。在许多感兴趣的情况下，对朗登预测的吸收率降低的修正很大；例如，在Z = 6和Tₑ = 400eV时，朗登对吸收率的预测误差约为2倍。然而，我们也考虑了等离子体屏蔽的额外效应，该效应预测吸收率会降低类似的量（高达约30%）。这两种效应相互竞争以确定整体吸收率，整体吸收率可能会增加或降低，具体取决于条件。通过用一个依赖于超高斯阶数“M”和屏蔽长度的解析表达式替换常用的库仑对数，这些修正可以纳入辐射流体动力学模拟代码中。
