Energy loss of correlated ions in plasmas: Collective and individual contributions

Stopping-power enhancement from discrete particle-wake correlations in high-energy-density plasmas

Three-dimensional (3D) simulations of electron beams propagating in high-energy-density plasmas using the quasistatic Particle-in-Cell (PIC) code QuickPIC demonstrate a significant increase in stopping power when beam electrons mutually interact via their wakes. Each beam electron excites a plasma wave wake of wavelength ∼2πc/ω_{pe}, where c is the speed of light and ω_{pe} is the background plasma frequency. We show that a discrete collection of electrons undergoes a beam-plasma-like instability caused by mutual particle-wake interactions that causes electrons to bunch in the beam, even for beam densities n_{b} for which fluid theory breaks down. This bunching enhances the beam's stopping power, which we call "correlated stopping," and the effect increases with the "correlation number" N_{b}≡n_{b}(c/ω_{pe})^{3}. For example, a beam of monoenergetic 9.7 MeV electrons with N_{b}=1/8, in a cold background plasma with n_{e}=10^{26}cm^{-3} (450 g cm^{-3} DT), has a stopping power of 2.28±0.04 times the single-electron value, which increases to 1220±5 for N_{b}=64. The beam also experiences transverse filamentation, which eventually limits the stopping enhancement.

Stopping power of dense plasmas: The collisional method and limitations of the dielectric formalism

We present a study of the stopping power of plasmas using two main approaches: the collisional (scattering theory) and the dielectric formalisms. In the former case, we use a semiclassical method based on quantum scattering theory. In the latter case, we use the full description given by the extension of the Lindhard dielectric function for plasmas of all degeneracies. We compare these two theories and show that the dielectric formalism has limitations when it is used for slow heavy ions or atoms in dense plasmas. We present a study of these limitations and show the regimes where the dielectric formalism can be used, with appropriate corrections to include the usual quantum and classical limits. On the other hand, the semiclassical method shows the correct behavior for all plasma conditions and projectile velocity and charge. We consider different models for the ion charge distributions, including bare and dressed ions as well as neutral atoms.

Laser-assisted stopping power of a hot plasma for a system of correlated ions

The laser-assisted stopping power of a fully ionized plasma for the system of two correlated test charges is investigated. The general expressions for the stopping power are applied to a low-density and a low-temperature plasma in a low-energy beam-plasma experiment [J. Jacoby et al., Phys. Rev. Lett. 74, 1550 (1995)]. The effect of the interaction between the beam test charges, described by a correlation term, is to increase the stopping power of the laser-assisted plasma compared to the case where the charges are infinitely separated. However, the laser field affects the correlation between the test charges and contributes to decrease the plasma stopping power, as compared to the laser-free dicluster case.