Atomic physics for beam-target interactions

Abstract

This survey is devoted to a few basic atomic problems associated with the stopping of nonrelativistic pointlike ions in dense and hot matter, and also to the Stark broadening diagnostics of the resulting beam-produced plasmas.First, we consider the free electron contribution, taken in the RPA approximation with an exact dynamic dielectric function, valid at any temperature. Therefore, we obtain stopping power and straggling for any projectile velocity. The temperature dependence is of special relevance for a projectile energy smaller than 5 MeV/a.m.u.Next, we revise the Barkas effect (Z3 corrections) through a novel and compact formulation, which is based on an analogy with electron impact broadening theory. It facilitates inclusion of the non hydrogenic and electronic structure of the target ions, in a more selective way. The results may increase the usual Z2-stopping by 15 to 30 per cent corrections.Then, we show how the Stark broadening diagnostics of the compressed D + T fuel, seeded with high Z species, arising from the surrounding envelopes, may provide accurate determination of the electron number density ne. In this connection, it should be appreciated that the relatively long compression times (≃ 20 nsec) suggested by the HIBALL numerical simulation allow for a nearly Local Thermodynamic Equilibrium (LTE) state in the target, with Te ≃ Ti. As a consequence, spectroscopic measurements are expected to be easier to implement in HIF targets, than in laser ones.A tentative proposal for the use of Stark broadening diagnostics of inflight excited and highly stripped ion projectiles is displayed in § 5.Experiments involving an HIB produced by a standard accelerator, and interacting with an independently produced coronal plasma are finally outlined.