The effect of ion drift on the sheath, presheath, and ion-current collection for cylinders in a collisionless plasma

A calculation is presented of the behavior of the sheath and presheath surrounding an infinite cylindrical conducting object, representing a spacecraft or electrostatic probe, which is moving transversely through a collisionless plasma, such as is encountered in the ionosphere. The calculation is done by solving the coupled Vlasov (collisionless Boltzmann) and Poisson equations in an iterative manner. The results show that for some ratios of probe radius to electron Debye length, the ion current collected by the probe in a drifting plasma can be less than that collected in a nondrifting plasma. These changes in the current-collection behavior can be linked to changes that occur in the sheath and presheath with plasma drift, including at large enough drift speeds the disappearance or “collapse” of the presheath.