ECAMP 15

The electron collision experiments provide essential information on the structure of the bombarded objects. The obtained data on the cross-sections of the studied process are a valuable addition to information obtained using the optical spectroscopy technique. Such data can be found both numerically and experimentally. The measurements usually involve bombarding the selected target with a beam of electrons and detecting the non-scattered electrons (transmission methods) or scattered electrons (crossed beams technique). Cross-fired or cell experiments are relatively simple for the neutral target. The situation becomes more complicated if one considers the electron impact on ions. It is generally difficult to provide a beam of ions of sufficiently well-defined geometry and density, allowing the detection of scattered electrons with good statistics. These are the main reasons for only a few experiments on electron collisions with singly charged ions.
On the other hand, there are several theoretical datasets on calcium ion ionization [1–4]. Moreover, the data on the ionization of ions may be especially interesting, as, besides direct ionization, one can observe autoionizing processes, which play a significant role in the process at specific energies.
An ion trap can be used as a container for target ions to overcome this problem. In this case, the target can be detected instead of the projectile, which can be achieved using optical methods similar to depletion spectroscopy [5]. In electron-atom/ion collision experiments, cross-section data are typically presented as a function of electron energy. Therefore, precise energy control of the monochromatic electron beam is important as it determines the quality of the obtained data. Unfortunately, the RF field used in the trap can disturb both the energy and electron trajectories. Therefore, optimizing the system in this respect is crucial for the quality of the obtained data.
We present a new experimental system using a quadrupole ion trap with an integrated electron gun. In the applied geometry, the electron beam is emitted along the axis of the trap, which reduces the energy spread of electrons and thus increases the accuracy of measurements.

[1] P.G. Burke, A.E. Kingston, A. Thompson, Electron impact ionisation of Ca+, J.Phys. B: At. Mol. Phys. 16 (13) (1983) L385–L389.
[2] D.C. Griffin, M.S. Pindzola, C. Bottcher, Calculations of the contributions of excitation-autoionisation to the electron impact ionisation of Ca+ and Ba+ in the distorted-wave approximation, J. Phys. B: At. Mol. Phys. 17 (15) (1984) 3183–3191.
[3] M.S. Pindzola, C. Bottcher, D.C. Griffin, Indirect processes in the electron impact ionisation of Ca+ using an LS-term-dependent close-coupling method, J. Phys. B: At. Mol. Phys. 20 (14) (1987) 3535–3545.
[4] N.R. Badnell, D.C. Griffin, M.S. Pindzola, Electron impact ionization of Ca+, J.
Phys. B: At. Mol. Opt. Phys. 24 (11) (1991) L275
[5] Ł. Kłosowski, M. Piwiński, Experimental method for determination of the integral cross-section for electron impact ionization of ions with optical control of the target’s initial quantum state, J. Electron. Spectrosc. Relat. Vol. 260, 147239 (2022), p. 1-8