Stimulated Raman scattering: Action evolution and particle trapping via Euler–Vlasov fluid simulation
Abstract
The Manley–Rowe action relations and trapped‐electron orbit theory have been applied to the problem of stimulated Raman scattering (SRS) in the forward direction, as simulated by an Euler–Vlasov fluid (EVF) code in periodic geometry. After a slight initial delay, the Vlasov results agree well with three‐oscillator theory (but with damping larger than the Landau linear value). The action sum of the pump and the scattered SRS wave was well conserved, while the action loss between the pump and plasma wave was shown to be well accounted for in detail by examining the electron energy for electrons above the lower trapping boundary (separatrix) in x‐px phase space. However, unlike the three‐oscillator model, the action sum of the pump and plasma wave was observed to actually increase for a short time because of retrieval of apparently lost action from the trapped‐electron effect in regenerating the plasma wave. Thus the utility was clearly demonstrated of using action conservation to separate the effects of three‐wave interaction from those due to nonlinear particle–wave interaction. The EVF code also shows clearly the fine details of layering and folding seen in x‐px phase space due to electron trapping, detrapping, and retrapping. [These details would have been invisible in the usual particle‐in‐cell (PIC) code because of graininess at low phase space densities.]
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