Interaction of Cooled Ion Beams with Internal Fiber Targets

Beam lifetime considerations and the limits of electron cooling restrict the thickness of internal targets to 1015 atoms/cm2. Gas jets or diffuse gas targets are possible schemes, but require a major technical effort to maintain sufficient vacuum adjacent to the target region. In addition, some important target materials are not available as gases. Dust targets have been used successfully, but are comparable to gas targets in the required technical effort. Fiber targets are a relatively easy way to present certain target nuclei (such as 12C, 28 Si, 5 4 C ~ ) to the stored beam. For fiber targets the idea is that the passage of a beam ion through a relatively thick object can be tolerated as long as the particle misses the fiber often enough. This allows sufficient cooling in many turns around the ring. For simplicity we consider a vertical fiber of linear density 6 (atoms/cm) positioned at the center of the stored beam, whose horizontal width is 2ao. Then the average target thickness is1 2 t d = rao