Vlasov code development with inertial confinement fusion applications
Experiments probing fundamental laser-plasma interaction physics have demonstrated some interesting and unexpected effects. Scattering from electron plasma waves with frequencies below the electron plasma frequency (called electron acoustic waves) has been observed in addition to conventional parametric scattering. Reflectivities observed in NIF early light experiments on long scale-length plasmas differed considerably from those predicted by existing fluid models. These effects are essentially kinetic in nature. The low frequency modes are supported by the trapping of electrons at low phase velocities and the saturation of instabilities at the intensities provided by the next generation of laser systems, such as NIF, is associated with the trapping of electrons. Numerical simulation of laser plasma interaction, therefore, benefits from an accurate treatment of the particle kinetics, in particular the evolution of the particle distribution functions. The direct solution of the Vlasov equation allows a high resolution, noise-free, representation particle distribution functions. Recent advancements in Vlasov codes, which draw a considerable expertise in the numerical solution of hydrodynamic codes, make such an approach to the simulation of laser plasma interaction viable. Here the development of a one dimensional electromagnetic Vlasov code is outlined. Thecode is applied to realistic laser and plasma parameters characteristic of single hot-spot experiments. Results are in qualitative agreement with experiments displaying both stimulated Raman and stimulated electron acoustic scattering [N. J. Sircombe, T. D. Arber and R. O. Dendy Kinetic effects in Laser-Plasma coupling: Vlasov theory and computations, Submitted to Plasma Physics and Controlled Fusion]. The amplitude of simulated electron acoustic waves is greater than that observed experimentally, and is accompanied by a higher phase velocity. These minor differences may be attributed to the limitations of a one-dimensional collisionless model. Furthermore, the interaction of a Langmuir wave with a density hole is investigated and shown to result in the acceleration of a small population of electrons [N. J. Sircombe, T. D. Arber and R. O. Dendy, Accelerated electron populations formed by Langmuir wave-caviton interactions, Phys. Plasmas, 12, 012303 (2005)]. This acceleration results from wave breaking and is dependent on the parameters of the background density profiles. In addition, pre-acceleration of electrons in supernova remnant shocks is considered as a kinetic problem [N. J. Sircombe, M. E. Dieckmann, P. K. Shukla and T. D. Arber, Stabilisation of BGK modes by relativistic effects, Astronomy and Astrophysics, In Press], [M. E. Dieckmann, N. J. Sircombe, M. Parviainen, P. K. Shukla and R. O. Dendy, Phase speed of electrostatic waves: The critical parameter for efficient electron surfing acceleration, Plasma Phys. Control.