Low Energy Charge Transfer With Multi-Charged Ions Using Merged Beams

摘要

Charge transfer by multi-charged ions from neutrals is important in many types of plasmas, including those in material processing, lighting, ion source development, magnetic fusion, and astrophysics. Our current ability to reliably predict low-energy charge transfer relies on our understanding of the dynamics and our ability to model the quasi-molecular states formed during collisions. The ion-atom merged-beams apparatus together with the intense ion beams made available by the ORNL ECR ion source provide a unique opportunity to study charge transfer at low (meV/u to keV/u) collision energies. Experimental and theoretical evaluation of the recent ORNL benchmark measurements of the charge transfer cross sections for He2+, N2+, Ne2+, Ne3+, Ne4+ + H(D) are presented. The measured cross sections for Ne3+, Ne4+, N2+ + D show a strong increase toward low energies which is attributed to the ion-induced dipole attraction between reactants. The Ne2+, He2+ + H(D) systems show a sharply decreasing cross section toward lower energies where the effects of rotational coupling are evident and can be studied. The ECR ion source facility is being upgraded to provide high energy multicharged ion beams at (20–250) × q keV. The higher velocity beams will allow measurements with heavier ions and allow measurements to be performed with both H and D to directly test predicted isotope effects at low energies. With the recent addition of a Cs-negative ion source to the ion-atom merged-beams apparatus, eV/u collisions between multi-charged ions and multi-electron targets are being explored. Preliminary measurements of Ar2+ + Li are presented.