The reduced-description particle-in-cell model for the two plasmon decay instability

Recently, motivated by the resurgent interest in suprathermal electron generation by two plasmon decay (TPD) in direct-drive laser-fusion [J. A. Delettrez et al., Bull. Am. Phys. Soc. 53, 248 (2008); V. A. Smalyuk et al., Phys. Rev. Lett. 100, 185005 (2008); B. Yaakobi et al., Phys. Plasmas 12, 062703 (2005)], the fully kinetic, reduced-description, particle-in-cell (RPIC) methodology has been extended to include TPD. It provides a computationally efficient fully kinetic simulation tool, especially in nonlinear regimes where the Langmuir decay instability (LDI) is a dominant saturation mechanism. This RPIC methodology is an extension of the modeling of laser-plasma instabilities in underdense plasmas reported previously [H. X. Vu, B. Bezzerides, and D. F. DuBois, J. Comput. Phys. 156, 12 (1999)]. The relationship between RPIC and the extended Zakharov model previously used for TPD [D. F. DuBois, D. A. Russell, and H. A. Rose, Phys. Rev. Lett. 74, 3983 (1995)] is explored theoretically and tested in simulations. The modification of the electron velocity distribution - in particular, the generation of hot electrons - as calculated in RPIC leads to weakening of the wave turbulence excited by TPD compared to the Zakharov model predictions but the locations in wave vector space of important spectral features, e.g., arising from the LDI, of the nonlinear wave fluctuations are exactly the same in the two approaches. New results involving two oblique, overlapping laser beams, a common geometrical feature in direct-drive schemes, are presented. The two laser beams can cooperatively excite common primary Langmuir waves which initiate the LDI process.