Accelerators and ion storage ring TSR
Stored ion species
Overview of beam lifetimes
The main processes affecting the lifetime of a stored ion beam are electron capture in the residiul gas and in the electron cooler as well as stripping reactions and single scattering. Multiple scattering does not play a role since it is compensated by electron cooling. The average residual gas pressure in the TSR is 4 - 7E-11 mbar. The following table shows measured lifetimes for some stored ion species. For 21 MeV protons a beam lifetime of 60 hours was reached with electron cooling. A lifetime between 14 and 48 s was measured for singly charged ions: Li+, Be+ and Mg+. The reason for these short lifetimes are stripping reactions in the residual gas. With increasing charge of the ions the cross sections of capture processes increase. The main processes affecting the lifetime, for example 35Cl17+ ions, are electron capture in the residual gas and electron capture in the electron cooler. The heaviest ion species stored were 197Au50+ and 197Au51+. Without electron cooling a beam lifetime of 68s was measured for the charge state 50+. The lifetime was dramatically reduced to 3s with optimized electron cooling. This can be explained by dielectronic resonances at relative energy zero between electron and ion beam.
|Ion||Energy [MeV]||uncooled [sec]||cooled [sec]|