TIME-DEPENDENT STOPPING POWER AND INFLUENCE OF AN INFINITE MAGNETIC-FIELD

Using the dielectric theory for a weakly coupled plasma we investigate the time-dependent behavior of the stopping power on a moving ion in a classical plasma. Special emphasis is placed on the transient proper ties between the onset of the external distortion (ion) and the statio nary regime of constant stopping. It is shown that after a characteris tic time of approximately a quarter of a plasma period tau(p) the stop ping power has reached its stationary value for a wide range of projec tile velocities upsilon(p) and coupling constants Z = Z(p)/(4 pi n(0) lambda(D)(3)) (where Z(p) is the charge number of the projectile, n(0) the electron density, and lambda(D) the Debye length). For small velo cities upsilon(p) the stopping power then shows damped oscillations ab out the stationary value. Comparisons with the case of a one-dimension al dynamic associated with an infinite magnetic field show no signific ant further delay in this transient behavior. This result is confirmed by a phase mixing approximation: deviations from the stationary value occur with the same t(-3/2) law in either case. Furthermore, we prese nt a Taylor series expansion for very short times where the pole expan sion approach reaches its limits. Molecular-dynamics computer simulati ons have been done for the case without magnetic field. They are in go od agreement with the theoretical results for weak coupling and reveal the importance of nonlinear effects for stronger coupled plasmas (Z m uch greater than 1).