Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations

Abstract

Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E Â B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (x pe < x ce ). A large drift velocity (Mach 4.5 with respect to the ion acoustic speed) between the plasma and probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship. [http://dx.

A parallel particle-in-cell code for spacecraft charging problems

“…Finally, a wake region and another electron depletion wing are present in the ion-rich wing region. These flow patterns are consistent with the results by Heinrich & Cooke (2013), except the second electron depletion wing is in the ion-rich wing region. These discrepancies only appear in the combined charge density profile, and only net positive charges are visible in the ion-rich wing region, obscuring the presence of an electron depletion region.…”

“…As shown, after a certain simulation step, a relatively steady stage is reached with small current fluctuations. The collected current is approximately 3 mA (1.5 mA × 2), close to the predicted value of 4 mA by Heinrich & Cooke (2013). The small difference is because Heinrich adopted the entire right boundary face to inject electrons into the simulation box, resulting in enhanced electron collections parallel to the magnetic field.…”

“…Cases III and IV are about numerical investigations of practical plasma flow problems, and they are associated with more complicated E × B drifting plasma flows. These four cases correspond to the work done by Singh, Vashi & Leung (1994), Laframboise (1966), Singh, Leung & Vashi (1997) and Heinrich & Cooke (2013).…”

“…−9900 ω ce = 100ω pe (rad s −1 ) 8 × 10 9 U drift (10 5 m s (Heinrich & Cooke 2013). It is an under-dense plasma flow over a positively charged probe which is characterized by: r e < r p , r i < r p and ω pe < ω ce .…”

“…Two benchmark test cases with analytical solutions are selected to validate the codes and demonstrate their capabilities. After that, we present two more advanced cases, dilute plasma flows over positively charged probes with electric field (E) × magnatic field (B) drifting velocities (Singh, Leung & Singh 2000;Heinrich & Cooke 2013). They are practical problems with space engineering applications.…”