| AVS 64th International Symposium & Exhibition | |
| Vacuum Technology Division | Thursday Sessions |
| Session VT-ThA |
| Session: | Surface Science for Accelerators |
| Presenter: | Markus Bender, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany |
| Authors: | M. Bender, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany H. Kollmus, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany E. Mahner, CERN, Switzerland |
| Correspondent: | Click to Email |
Dynamic pressure increases in vacuum systems of particle accelerators have been observed since almost 50 years. Since the turn of the millennium, the dynamic vacuum turned out to be an intensity limitation in particle accelerators, e.g. in the Low Energy Antiproton Ring (LEAR) at CERN or the heavy ion synchrotron SIS18 at GSI. Here, charge exchanged lost beam ions stimulate the release of gas from the chamber walls and the subsequent pressure increase leads to increased beam-loss. Hence the effect is self-amplifying and can lead to severe deterioration of the vacuum to the point of complete beam-loss. Consequently heavy ion-induced desorption is an issue for next-generation heavy ion accelerators such as the FAIR facility or Spiral2 with highest beam intensities.
To come up against this dynamic vacuum effect, several measures have been conducted. In particular the physics behind the ion-induced release of gas was investigated. For that purpose, several samples have been irradiated with ion beams of different parameters and the resulting desorption yields have been measured. A broad range from some 10 to several 10,000 released gas molecules per incident ion was observed. From the gathered results a clear picture of the underlying process of ion-induced desorption was drawn. It could be shown that the desorbed gas is originating mainly from the surface or surface-close regions of the target. But in contrast to earlier ideas, sputtering of the oxide layer on metals was not identified as the source for the desorbed gas. Latest experiments prove that pre-treatment of critical components is most important to minimize the desorption yield and therefore, especially thermal annealing was investigated in detail.
Besides experimental findings a model calculation was developed that is able to describe and compare desorption yields of different collision systems. The calculation is based on the inelastic thermal spike model and describes ion-induced desorption as enhanced thermal desorption due to a transient overheated spot around the ion impact.
Presently we are able to propose materials, coatings, and treatment procedures for best performance in particle accelerator vacuum systems.