Energy loss of heavy ions in strongly coupled plasmas

Abstract

We investigate the energy loss of heavy ions in strongly coupled plasmas, by performing molecular dynamics (MD) computer simulations. These studies are of interest in heavy-ion-driven inertial confinement fusion, as well as for electron cooling. We consider the non-linear behavior for strong target-ion coupling parameters, i.e. ZΓ 3 2 ,≳ 1 , in non-ideal plasmas with Γ ≳ 0.1 ( Z is the charge number of the ion and Γ is the plasma parameter of the target). The new features that we found from our simulation results can be summarized as follows. (1) For strong ion-target coupling, the energy loss of the ions at low velocities scales with Z as Z 1.5, in agreement with recent experimental and other theoretical results. This clearly deviates from the Z 2 ln( const. Z ) scaling of the conventional weak coupling theories. (2) The change in the Z scaling has its origin in a non-linear screening that occurs for strong coupling and is associated with an increase in the (static) screening length above the Debye-Hückel result of the linear theory. (3) The non-linear screening is accompanied by electrons trapped by the ion into high Rydberg states, through multi-particle collisions. Compared with the case of linear coupling, this trapping causes an enhanced electron density around the ion. (4) The transient time dependence of the stopping power after switching on the ion-target interaction has characteristic time-scales that are a fraction of the plasma period.