Initial Expansion of a Magnetic Bubble

The mini-magnetosphere plasma propulsion scheme (plasma sail) involves the inflation of a magnetized plasma bubble attached to a satellite in space that is large enough to deflect the solar wind and consequently achieve velocities on the order of 50 km/s [Winglee et al., JGR, 2000]. Here we present simulations of the initial expansion of the magnetic bubble in a simplified geometry. We consider plasma injected into a stationary magnetized background plasma in the presence of a dipole magnetic field with a 2-D kinetic ion, massless fluid electron (hybrid) electromagnetic code. For small values of the dipole field, the injected ions exclude the ambient magnetic field and plasma to form a diamagnetic cavity. For large magnetic dipoles, the injected ions remain magnetized and produce additional plasma currents that expand the dipole field, leading to a magnetic bubble. A criterion to distinguish between these two regimes is derived. Issues associated with the sensitivity of symmetry of the bubble that is formed to the plasma injection scheme are also discussed.