ASPEN: A fully kinetic, reduced-description particle-in-cell model for simulating parametric instabilities

A fully kinetic, reduced-description particle-in-cell (RPIC) model is prese nted in which deviations from quasineutrality, electron and ion kinetic eff ects, and nonlinear interactions between low-frequency and high-frequency p arametric instabilities are modeled correctly The model is based on a reduc ed description where the electromagnetic field is represented by three sepa rate temporal envelopes in order to model parametric instabilities with low -frequency and high-frequency daughter waves. Because temporal envelope app roximations are invoked, the simulation can be performed an the electron ti me scale instead of the time scale of the light waves. The electrons and io ns are represented by discrete finite-size particles, permitting electron a nd ion kinetic effects to be modeled properly. The Poisson equation is util ized to ensure that space-charge effects are included. The RPIC model is fu lly three dimensional and has been implemented in two dimensions on the Acc elerated Strategic Computing Initiative (ASCI) parallel computer at Los Ala mos National Laboratory and the resulting simulation code has been named AS PEN. We believe this code is the first particle-in-cell code capable of sim ulating the interaction between low-frequency and high-frequency parametric instabilites in multiple dimensions. Test simulations of stimulated Raman scattering, stimulated Brillouin scattering, and Langmuir decay instability are presented.