The full R.P.A. dielectric function (rs < 1) is introduced in a calculation for stopping of pointlike and nonrelativistic positive ions in a homogeneous and dense electron fluid at any temperature. Results are given for values of degeneracy αe = μ/kB T. Accurate asymptotic expressions are worked out in the small and large projectile velocity limits. Simple interpolation formulae are displayed. The replacement of Fermi statistics by Boltzmann is also investigated for any temperature. Contact is achieved with previous high- and low-temperature approximations. The Jackson limit is recovered at T → ∞ and is modified in order to fit the full range of target densities and projectile velocities of interest. Relevance to heavy ion driven fusion is stressed throughout

International audienceThe advent of X-ray free-electron lasers has granted researchers an unprecedented access to theultrafast dynamics of matter on the nanometre scale(1-3). Aside from being compact, seededplasma-based soft X-ray lasers (SXRLs) turn out to be enticing as photon-rich(4) sources (up to 10(15)per pulse) that display high-quality optical properties(5,6). Hitherto, the duration of these sources waslimited to the picosecond range(7), which consequently restricts the field of applications. This bottleneckwas overcome by gating the gain through ultrafast collisional ionization in a high-density plasmagenerated by an ultraintense infrared pulse (a few 10(18) W cm(-2)) guided in an optically pre-formedplasma waveguide. For electron densities that ranged from 3 x 10(18) cm(-3) to 1.2 x 10(20) cm(-3), thegain duration was measured to drop from 7 ps to an unprecedented value of about 450 fs, which pavesthe way to compact and ultrafast SXRL beams with performances previously only accessible inlarge-scale facilities