Collisionless ion collection by non-emitting spherical bodies in E x B fields

[摘要] (cont.) The finite shielding length regime is more complex, and an important transition in plasma structure occurs when the Debye length goes over the average ion Larmor radius. Studies of ion collection show that the ion current can exceed the (unmagnetized) OML limit at weak magnetization, and the Mach probe calibration method proposed in the context of quasineutral plasmas holds up to Debye lengths equal to about 10% of the probe radius. A further analysis consists in calculating the force exerted by the flow on spherical dust. In short Debye length plasmas a strong drag component antiparallel to the convective electric field forms, causing the dust to spin faster than what predicted by its Larmor frequency. At intermediate and large Debye length the ion-drag in the direction of transverse flow is found to reverse in subsonic conditions, but the internal Laplace force appears to be positive, and larger in magnitude than the negative ion-drag.

[发布机构] Massachusetts Institute of Technology