Interaction of a test particle with a magnetized plasma

In the presence of a sufficiently strong magnetic field, the shielding of a test particle in a two-dimensional Vlasov plasma disappears. An intermediate regime is investigated, for both a stationary and a moving test particle, in which the plasma frequency ω_p and the cyclotron frequency ω_c are of the same order of magnitude. In the case of a stationary test particle, this intermediate regime is approximately in the range ½ ≤ a ≤ 2, where a = ω_p/ω_c. For a < ½, only partial shielding occurs, the potential retaining its vacuum logarithmic dependence. For a < 2, the potential approximates to the field-free case, and falls off exponentially. For a test particle moving at electron thermal speed, the typical bow wave and wake phenomenon, associated with an unmagnetized plasma, is no longer present. We find, instead, that the potential possesses upstream—downstream symmetry.