LINEARIZED POTENTIAL OF AN ION MOVING THROUGH PLASMA

The solution of the linearized Vlasov-Poisson equations describing a projectile ion moving through a classical isotropic electron plasma is investigated analytically and numerically for a wide range of projectile velocities v(p). Extending the range of earlier computations considerably, our calculations were performed for velocities up to v(p) = 15v(th), showing the wake field behind the ion for distances 0-less-than-or-equal-to-d-less-than-or-equal-to-200-lambda-D, where v(th) is the thermal electron velocity and lambda-D the Debye length of the plasma. As a new feature, we demonstrate that the amplitude of the wake field in the region v(p)/v(th) less-than-or-equal-to d/lambda-D less-than-or-equal-to 2/3(v(p)/v(th))3 is almost undamped, and only for larger distances from the ion does it take the 1/d behaviour shown in other work. Thus the wake field of a single ion persists for much longer than previously thought. The question of whether this effect could have practical consequences, for example, for ion-beam cooling, is briefly addressed.