Search

We study the electron-loss-to-continuum (ELC) cusp experimentally and theoretically by comparing the ionization of U$^{89+}$ projectiles in collisions with N$_2$ and Xe targets, at a beam energy of 75.91 MeV/u. The coincidence measurement between the singly ionized projectile and the energy of the emitted electron is used to compare the shape of the ELC cusp at weak and strong perturbations. A significant energy shift for the centroid of the electron cusp is observed for the heavy target of Xe as compared to the light target of N$_2$. Our results provide a stringent test for fully relativistic calculations of double-differential cross sections performed in the first-order approximation and in the continuum-distorted-wave approach.

Absolute cross sections for electron-impact single ionisation (EISI) of multiply charged tungsten ions (W$^{q+}$) with charge states in the range $ 11 \leq q \leq 18$ in the electron-ion collision energy ranges from below the respective ionisation thresholds up to 1000~eV were measured employing the electron-ion crossed-beams method. In order to extend the results to higher energies, cross section calculations were performed using the subconfiguration-averaged distorted-wave (SCADW) method for electron-ion collision energies up to 150~keV. From the combined experimental and scaled theoretical cross sections rate coefficients were derived which are compared with the ones contained in the ADAS database and which are based on the configuration-averaged distorted wave (CADW) calculations of Loch et al. [Phys. Rev. A 72, 052716 (2005)]. Significant discrepancies were found at the temperatures where the ions investigated here are expected to form in collisionally ionised plasmas. These discrepancies are attributed to the limitations of the CADW approach and also the more detailed SCADW treatment which do not allow for a sufficiently accurate description of the EISI cross sections particularly at the ionisation thresholds., Comment: 14 pages, 4 figures, 4 tabels