3-DIMENSIONAL ELECTROMAGNETIC MONTE-CARLO PARTICLE-IN-CELL SIMULATIONS OF CRITICAL IONIZATION VELOCITY EXPERIMENTS IN-SPACE

Although the existence of the critical ionization velocity (CIV) is kn own from laboratory experiments, no agreement has been reached as to w hether CIV exists in the natural space environment. In this paper we m ove towards more realistic models of CIV and present the first fully t hree-dimensional, electromagnetic particle-in-cell Monte-Carlo collisi on (PIC-MCC) simulations of typical space-based CIV experiments. In ou r model, the released neutral gas is taken to be a spherical cloud tra veling across a magnetized ambient plasma. Simulations are performed f or neutral clouds with various sizes and densities. The effects of the cloud parameters on ionization yield, wave energy growth, electron he ating, momentum coupling, and the three-dimensional structure of the n ewly ionized plasma are discussed. The simulations suggest that the qu antitative characteristics of momentum transfers among the ion beam, n eutral cloud, and plasma waves is the key indicator of whether CIV can occur in space. The missing factors in space-based CN experiments may be the conditions necessary for a continuous enhancement of the beam ion momentum. For a typical shaped charge release experiment, favorabl e CIV conditions may exist only in a very narrow, intermediate spatial region same distance from the release point due to the effects of the cloud density and size. When CIV does occur, the newly ionized plasma from the cloud forms a very complex structure due to the combined for ces from the geomagnetic field, the motion induced emf, and the polari zation. Hence the detection of CIV also critically depends on the sens or location.