Multifluid Simulation of Ion Acoustic Solitons Arising From a Charged Source and Comparison to the Forced Korteweg-de Vries Model
Ian DesJardin, University of Maryland, College Park
Ion acoustic solitons can be generated by a charged object immersed in an electrostatic quasineutral two-temperature plasma flow. These are often described by the forced Korteweg-de Vries equation. Multifluid simulations of this scenario using the PPPL Gkeyll code are conducted and compared to numerical solutions of the forced Korteweg-de Vries equation and theoretical predictions. The forced Korteweg-de Vries equation description is found to be in mostly good agreement with multifluid simulation. As in forced Korteweg-de Vries theory, flow regimes are observed where either precursor or pinned solitons are generated depending on the background bulk velocity and debris size. However, the critical velocities that govern phase transitions from linear to precursor and precursor to pinned solitons are found to differ substantially with precursor solitons being much more likely to be produced than previously thought. New theory is derived for the supercritical transition speed. The precursor soliton limit cycle period is also found to be in disagreement with previous studies. A violation of the Korteweg-de Vries theory is discovered regarding the coupling of fluid quantities. Theory for the weak limit of this discrepancy is shown. Finally, we show that the moving solutions from the multifluid equations without the presence of a charged object can be exactly modeled by the Korteweg-de Vries equation under the appropriate coordinate transformations. These disagreements in theory have ramifications on the use of ion acoustic solitons to detect space debris.