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MS: Massenspektrometrie
MS 8: Ion Traps and High Precision Mass Spectrometry
MS 8.1: Vortrag
Freitag, 6. April 2001, 16:45–17:00, EB 202
Ion Beam Bunching and Cooling with REXTRAP — •Friedhelm Ames1, Georg Bollen2, Oliver Forstner3, Dieter Habs1, Gerhard Huber4, and Pit Schmidt4 — 1Sektion Physik, LMU München, D-85748 Garching — 2NSCL, Michigan State Univerity, East Lansing, MI48824-1321, USA — 3ISOLDE, CERN, CH-1211 Geneva — 4Institut für Physik, J. Gutenberg-Universität, D-55099 Mainz
The beam quality of radioactive ion beams produced by present target ion source technology is often not sufficient for direct post acceleration. Furthermore, pulsed beams insure a more effective use of accelerators. In case of REX-ISOLDE, the post accelerator of the CERN-ISOLDE facility, a unique system for beam preparation is used. It consists of a gas filled Penning trap (REXTRAP) for bunching and cooling followed by an elctron beam ion source (EBIS) for charge state breeding. The Penning trap is placed on a high voltage platform near to 60 kV to decelerate the incoming beam of singly charged ions. Final stopping and accumulation in the center of the trap is accomplished by the energy loss provided by the buffer gas (≤ 10−3mbar Ar). Radial centring of the ions and thus reducing their transversal phase space volume can be achieved by applying an rf field at the ions cyclotron frequency. Beside the cooling effect this method offers the possibility of cleaning the beam from unwanted ion species. After an accumulation and cooling time of 10 to 100 ms a bunch of ions is released from the trap, accelerated again to 60 keV and transported to the EBIS. The efficiency achieved in the first tests was already more than 20 %. More than 107 ions per bunch can be accumulated, but at this high number space charge effects start influencing the cooling process and have to be taken into account.