The interaction of a moving spacecraft with the ionosphere: Current collection and wake structure

This thesis presents a numerical study of the interaction of a cylindrical probe, such as a spacecraft or a plasma diagnostic probe, with a collisionless, drifting Maxwellian plasma. The ion current collection and wake structure of such a moving probe are investigated over a range of plasma parameters simulating the plasma environment in the ionosphere. The numerical model takes into account the asymmetric sheath surrounding the probe and the effect of ion thermal motions.;The collected ion current is found theoretically to display a non-monotonic dependence on the drift velocity for an infinite cylindrical probe. The combined increasing ram-effect of drifting ions and shadowing effect of the probe are proposed to be the cause of this non-monotonic current behaviour.;A strong damping effect due to the ion thermal motions is seen to alter the wake structure significantly under various plasma parameters. The influences of varying the probe bias and drift velocity on the wake structure are also shown for different probe sizes.;Comparisons of our results with previous numerical and experimental works of other investigators are made when the latter are available.