Sentoku Y, Paraschiv I, Royle R, Mancini R C, Johzaki T
Department of Physics, University of Nevada, Reno, Nevada 89557, USA.
Graduate School of Engineering, Hiroshima University, Hiroshima Prefecture 739-8527, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Nov;90(5-1):051102. doi: 10.1103/PhysRevE.90.051102. Epub 2014 Nov 21.
The x-ray laser-matter interaction for a low-Z material, carbon, is studied with a particle-in-cell code that solves the photoionization and x-ray transport self-consistently. Photoionization is the dominant absorption mechanism and nonthermal photoelectrons are produced with energy near the x-ray photon energy. The photoelectrons ionize the target rapidly via collisional impact ionization and field ionization, producing a hot plasma column behind the laser pulse. The radial size of the heated region becomes larger than the laser spot size due to the kinetic nature of the photoelectrons. The plasma can have a temperature of more than 10 000 K (>1eV), an energy density greater than 10^{4} J/cm^{3}, an ion-ion Coulomb coupling parameter Γ≥1, and electron degeneracy Θ≥1, i.e., strongly coupled warm dense matter. By increasing the laser intensity, the plasma temperature rises nonlinearly from tens of eV to hundreds of eV, bringing it into the high energy density matter regime. The heating depth and temperature are also controllable by changing the photon energy of the incident laser light.
利用一种自洽求解光电离和X射线输运的粒子模拟程序，研究了低Z材料碳与X射线激光的相互作用。光电离是主要的吸收机制，产生的非热光电子能量接近X射线光子能量。光电子通过碰撞电离和场电离迅速使靶电离，在激光脉冲后产生一个热等离子体柱。由于光电子的动力学性质，加热区域的径向尺寸变得比激光光斑尺寸更大。等离子体的温度可以超过10000K（>1eV），能量密度大于10⁴J/cm³，离子-离子库仑耦合参数Γ≥1，电子简并度Θ≥1，即强耦合温稠密物质。通过增加激光强度，等离子体温度从几十电子伏特非线性上升到几百电子伏特，使其进入高能量密度物质区域。加热深度和温度也可以通过改变入射激光的光子能量来控制。
