KINETIC MODELING OF PLANAR PLASMA FLOWS WITH THE MONTE CARLO METHOD

P.D. Gasparyan, N.V. Ivanov
VANT. Ser.: Mat. Mod. Fiz. Proc 1997. Вып.1. С. 50.

      In target laser irradiation experiments of great interest is the process of collision „of plasma counter-flows. In the region of flow interaction mean ion ranges are known to be comparable with or higher than characteristics flow sizes. Therefore, to study this phenomenon, numerical techniques based on kinetic plasma models are needed. At the same time in unperturbed flow regions ion ranges are considerably less than the characteristic sizes and consideration of these regions at the kinetic level involves unacceptable computer costs. This, work proposes a technique for numerical computations of planar plasma flows where ion processes are considered at the kinetic level. It is based on the Monte Carlo method and involves about the same computer costs in the regions of low and high ion ranges.

      Since the mid 20-th century the need to account for reasons on unexpected brittle fracture has led to development of the linear fracture mechanics. A painful process of fracture criteria replacement began. The new criteria based on energetic relations required knowledge of presence of defects for an entity under consideration which considerably impeded their use and sometimes even made this impossible.
      The report presented critical consideration of some papers on space body failure description at interaction with the planet atmosphere. The use of conventional failure, criteria, such as critical shearing or breaking stresses, is shown to lead to inadequate description of a phenomenon as a whole. When using the integral approach based on meeting a needed energetic failure condition it is possible to adequately describe the qualitative phenomenon picture and also obtain quantitative results under certain conditions.
      Some requirements were formulated which the failure criteria should meet.

      This work studies interactions of powerful laser radiation with supercritical density plasma. At radiation rates of 10¹⁶ W/cm² the plasma dynamics under irradiation is severely non-linear, while at rates of 10¹⁸ W/cm² and higher relativistic effects become essential which motivates employment of computer experiment methods.
      To model processes (rates of 10¹⁸W/cm² and higher, the collisionless case, this work uses the developed electromagnetic codes implementing the particle method in the 2-D and 2^1/2D-gepmetry with account of electron relativism and ion mobility. The following was considered within a wide initial data range: normal and oblique radiation incidence; cases of planar and focused waves at various polarizations; evolution of processes on the density gradient. Some new effects were considered, such as generation of high-energy (MeV) electron fluxes on the boundary, generation of long-lived eddy structures in the plasma volume, excitation of higher harmonics on the boundary and, hence, laser radiation travel into dense plasma, essential dependence of dynamic processes on radiation polarization. Intense evolution of instabilities occurring on the density gradient was found to lead to generation of spatial structures in plasma. For oblique radiation incidence non-linear processes of plasma wave excitation and energy transfer to plasma are considered.
      To model kinetic processes (at rates up to 10¹⁶ W/cm²) with account of Coulomb collisions, developed computer codes are used which are based on Langevin equations stochastically equivalent to the original Focker-Plank equation. The collision effect on radiation absorption processes was analyzed.