Pitch‐angle scattering of cometary ions: Computer simulations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95535/1/grl5552.pd

Pitch angle scattering of cometary ions into monospherical and bispherical distributions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95043/1/grl5478.pd

Recalling and Updating Research on Diamagnetic Cavities: Experiments, Theory, Simulations

In the decade from the mid 80's to the mid 90's there was considerable interest in the generation of diamagnetic cavities produced by the sub-Alfvenic expansion of heavy ions across a background magnetic field. Examples included the AMPTE and CRRES barium releases in the magnetotail and magnetosphere as well as laser experiments at various laboratories in the United States and the Soviet Union. In all of these experiments field-aligned striations and other small-scale structures were produced as the cavities formed. Local and non-local linear theory as well as full particle (PIC), hybrid, and Hall-MHD simulations (mostly 2-D) were developed and used to understand at least qualitatively the features of these experiments. Much of this review is a summary of this work, with the addition of some new 3-D PIC and Hall-MHD simulations that clarify old issues associated with the origin and evolution of cavities and their surface features. In the last part of this review we discuss recent extensions of the earlier efforts: new space observations of cavity-like structures as well as new laboratory experiments and calculations with greatly improved diagnostics of cavities formed by expansions of laser-produced ions at super-Alfvenic speeds both across and along the background magnetic field

The directional dependence of cometary magnetic energy density in the quasi-parallel and quasi-perpendicular regimes

The direction of propagation of low frequency magnetic fluctuations generated by cometary ion pick-up is examined by means of one-dimensional electromagnetic hybrid simulations. The newborn ions are injected at a constant rate, and the helicity and direction of propagation of magnetic fluctuations are explored for cometary ion injection angles of 0[deg] and 90[deg] relative to the solar wind magnetic field. The parameter [eta] represents the relative contribution of wave energy propagating in the direction away from the comet, parallel to the beam. For small (quasi-parallel) injection angles [eta] was to found to be of order unity, while for larger (quasi-perpendicular) angles [eta] was found to be of order 0.5.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29538/1/0000626.pd

Hybrid simulations of plasmaspheric refilling including convection and injection

The interactions between upflowing thermal ions from conjugate ionospheres are modeled using a 1-dimensional hybrid particle code. The simulation model allows for multiple species, convection of plasmaspheric flux tubes, and Coulomb self collisions which conserve momentum and energy. Plasmaspheric refilling is studied, in which convection of the plasmaspheric flux tube and particle injection from an external source is included. The interaction of ionospheric thermal plasma and the injected plasma seems to play an important role in the evolution of the total particle distribution on the early time scales (t<1 hour).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30855/1/0000518.pd

Ion heating and energy partition at the heliospheric termination shock: hybrid simulations and analytical model

The Los Alamos hybrid simulation code is used to examine heating and the partition of dissipation energy at the perpendicular heliospheric termination shock in the presence of pickup ions. The simulations are one-dimensional in space but three-dimensional in field and velocity components, and are carried out for a range of values of pickup ion relative density. Results from the simulations show that because the solar wind ions are relatively cold upstream, the temperature of these ions is raised by a relatively larger factor than the temperature of the pickup ions. An analytic model for energy partition is developed on the basis of the Rankine-Hugoniot relations and a polytropic energy equation. The polytropic index {gamma} used in the Rankine-Hugoniot relations is varied to improve agreement between the model and the simulations concerning the fraction of downstream heating in the pickup ions as well as the compression ratio at the shock. When the pickup ion density is less than 20%, the polytropic index is about 5/3, whereas for pickup ion densities greater than 20%, the polytropic index tends toward 2.2, suggesting a fundamental change in the character of the shock, as seen in the simulations, when the pickup ion density is large. The model and the simulations both indicate for the upstream parameters chosen for Voyager 2 conditions that the pickup ion density is about 25% and the pickup ions gain the larger share (approximately 90%) of the downstream thermal pressure, consistent with Voyager 2 observations near the shock

Long-range attraction between particles in dusty plasma and partial surface tension of dusty phase boundary

Effective potential of a charged dusty particle moving in homogeneous plasma has a negative part that provides attraction between similarly charged dusty particles. A depth of this potential well is great enough to ensure both stability of crystal structure of dusty plasma and sizable value of surface tension of a boundary surface of dusty region. The latter depends on the orientation of the surface relative to the counter-ion flow, namely, it is maximal and positive for the surface normal to the flow and minimal and negative for the surface along the flow. For the most cases of dusty plasma in a gas discharge, a value of the first of them is more than sufficient to ensure stability of lenticular dusty phase void oriented across the counter-ion flow.Comment: LATEX, REVTEX4, 7 pages, 6 figure

Analysis of wave-particle interactions in a beam plasma system

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