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Stored and Cooled Ions Division
 
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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]
ion energy uncooled cooled
  [MeV] [sec] [sec]
p 21   220000
HD+ 2   24
HeH+ 2 5  
7Li+ 13.4 48  
9Be+ 7.3 35  
12C6+ 73.3   7500
CH+ 7   12
24Mg+ 3.6 14  
28Si14+ 115 260 540
32S16+ 195   450
35Cl17+ 202 366 318
63Cu26+ 510   166
80Se25+ 480   204
197Au50+ 695 68 3
197Au51+ 695 51 23