High-Resolution Electron Collision Spectroscopy with Multicharged Ions in Merged Beams

The Heidelberg ion storage ring TSR is currently the only ring equipped with two independent devices for the collinear merging of a cold electron beam with stored ions. This greatly improves the potential of electron-ion collision experiments, as the ion beam can be cooled with one electron beam, while the other one is used as a dedicated target for energy-resolved electron collision processes, such as recombination. The work describes the implementation of this system for first electron collision spectroscopy experiments. A detection system has been realized including an ion detector and specroscopic beam-control software and instrumentation. Moreover, in order to improve the spectroscopic resolution systematical studies of intrinsic relaxation processes in the electron beam have been carried out. These include the dependence on the electron beam density, the magnetic guiding field strength, and the acceleration geometry. The recombination measurements on low-lying resonances in lithiumlike Sc$^{18+}$ yield a high-precision measurement of the $2s-2p_{3/2}$ transition energy in this system. Operation of the two-electron-beam setup at high collision energy ($\approx 1000$~eV) is established using resonances of hydrogenlike Mg$^{11+}$, while the unique possibility of modifying the beam-merging geometry confirms its importance for the electron-ion recombination rate at lowest relative energy, as demonstrated on F$^{6+}$