Impact of slow multiply charged ions (MCI) on atoms, molecules and surfaces is of considerable interest in various fields of modern research as, e.g., thermonuclear fusion plasmas, astrophysical and ionospheric processes, and surface analytics and nanotechnology. To improve the understanding and permit the control of magnetically confined fusion plasmas, it is necessary to learn more about the relevance of multicharged impurity ions residing in these plasmas.
In the present work, a compact experimental setup has been constructed and utilized for measuring absolute cross sections for single (SEC) and double electron capture (DEC) in collisions of slow singly and multiply charged ions with gaseous atoms and molecules. Our technique combines collection of slow product ions with primary ion beam attenuation and stopping in a differentially pumped target gas chamber, where the pressure is measured by an absolutely calibrated capacitance manometer.
The primary ions are obtained from a 14.5 GHz all-permanent magnet electron cyclotron resonance (ECR) ion source with extraction geometry optimized for low ion beam energy.
Reliability of the new experimental setup has been checked by proof-of-principle measurements in comparison with well established resonant SEC cross section for impact of slow singly charged noble gas ions on their atoms (He, Ne, Ar). SEC and DEC cross sections have been investigated for impact of slow doubly charged ions on their own atoms (He, Ne, Ar), where resonant DEC is clearly the dominant reaction. Moreover, SEC and DEC for He2+ collisions with Ne have been studied, where at low impact energy SEC is expected to proceed via a single channel only. Additionally, collisions of He2+ with simple diatomic molecules (O2, H2 and D2) have been carried out, for which again SEC and DEC have been measured. A theoretical analysis based on Landau-Zener (LZ) theory and the extended over barrier model (EOBM) showed good agreement with results from this work, thereby providing additional insight in the physics behind these processes.
The present experimental and theoretical results are compared to values available in the literature and the results are discussed.