Blackett Laboratory, Imperial College London, Kensington, London SW7 2AZ, United Kingdom.
Phys Rev E. 2018 Aug;98(2-1):021201. doi: 10.1103/PhysRevE.98.021201.
We present kinetic two-dimensional Vlasov-Fokker-Planck simulations, including both self-consistent magnetic fields and ablating ion outflow, of a planar ablating foil subject to nonuniform laser irradiation. Even for small Hall parameters (ωτ_{ei}≲0.05) self-generated magnetic fields are sufficient to invert and enhance pressure perturbations. The mode inversion is caused by a combination of the Nernst advection of the magnetic field and the Righi-Leduc heat flux. Nonlocal effects modify these processes. The mechanism is robust under plasma conditions tested; it is amplitude independent and occurs for a broad spectrum of perturbation wavelengths, λ_{p}=10-100μm. The ablating plasma response to a dynamically evolving speckle pattern perturbation, analogous to an optically smoothed beam, is also simulated. Similar to the single-mode case, self-generated magnetic fields increase the degree of nonuniformity at the ablation surface by up to an order of magnitude and are found to preferentially enhance lower modes due to the resistive damping of high mode number magnetic fields.
我们呈现了包括自洽磁场和消融离子流在内的二维动力学 Vlasov-Fokker-Planck 模拟,研究了受非均匀激光照射的平面消融箔。即使 Hall 参数很小(ωτ_{ei}≲0.05),自生磁场足以反转并增强压力扰动。模式反转是由磁场的 Nernst 输运和 Righi-Leduc 热流的组合引起的。非局部效应会改变这些过程。在测试的等离子体条件下,该机制具有鲁棒性;它与幅度无关,并且发生在广泛的扰动波长范围内,λ_{p}=10-100μm。还模拟了消融等离子体对动态演化斑纹模式扰动的响应,类似于光平滑光束。类似于单模情况,自生磁场通过高达一个数量级的方式增加了烧蚀表面的非均匀性,并且由于高模数磁场的电阻阻尼,发现自生磁场优先增强低阶模式。