Interaction of Highly-Charged Ions with Matter

The interaction of high-energy heavy-ions with matter is a topic of importance in many areas of science. For example, the mechanisms whereby highly ionized atoms de-excite and return to charge neutrality are of great concern in the design of thermonuclear fusion reactors, where energy transfer to impurity ions injected from the walls of the containment vessel can seriously affect the plasma stability. The development of materials for use in outer space must take into account the destructive effects of cosmic rays. Such considerations are particularly important in the application of miniaturized semiconductor devices, and may ultimately limit the size scale of electronic circuits, both in space and on earth. A detailed understanding of energy loss processes of heavy-ions is imperative in various applications of particle accelerators -including those relating to medical therapeutic techniques, and in the operation of ion storage rings.

Many of the important dynamic properties of highly-charged ions may be investigated under the well-defined conditions possible through the use of a particle accelerator. The ECR ion source and K500 cyclotron can provide beams of fully stripped ions up to Z = 30 and heavier ions up to U6s+. This capability opens many exciting prospects for exploring the interactions of highly-charged ions with atoms, molecules, and surfaces.
The atomic physics research program focuses on a variety of topics involving ion-atom and ion-molecule collisions, including (a) charge transfer mechanisms, (b) inner-shell ionization phenomena, (c) fragmentation of molecules, (d) charge state equilibration in gases and solids, and (e) atomic structure of few-electron ions. In addition to characterizing the fundamental properties of collisions involving highly-charged ions, these studies supply data needed for applications in other fields, such as wavelengths of atomic transitions, line identifications, transition probabilities, and cross sections for ionization, excitation, and electron transfer. Spectra from foil-excited heavy ion beams also contribute to the general understanding of atomic structure and they provide the resonance line systematics required for plasma diagnostic purposes as well as for the interpretation of astrophysical phenomena. From the theoretical point of view, experiments with highly-charged ions offer new possibilities for testing the accuracy of atomic structure calculations - especially those dealing with the effects of relativity, developing models of multi-electron exchange processes, and exploring the role of electron correlations.