Heavy-ion induced molecular desorption: a challenge for the LEIR vacuum system

by E. Mahner (CERN-AT)

Thursday 10 Jul 2003, 14:15 → 15:15 Europe/Zurich

AT Auditorium (CERN)

A dynamic pressure rise induced by the loss of heavy ions has been seen first in 1997 during Pb⁵⁴⁺ accumulation and cooling tests in the Low Energy Antiproton Ring (LEAR) at CERN. Beam-induced desorption limited the beam lifetime and the intensity in LEAR. In preparation of the heavy ion physics with the LHC, LEAR has to be converted into a Low Energy Ion Ring (LEIR). An average dynamic pressure of 3x10^-12 Torr is required around the LEIR ring to satisfy the requested 30 s beam lifetime. To achieve this very low gas density in LEIR an intensive experimental programme has been launched at CERN in 2001 to measure the molecular desorption yields of lead ions at 4.2 MeV/u, to understand the limitations observed in 1997, and to prepare the LEIR vacuum system for heavy ion operation. Very large desorption yields of up to 2x10⁴ molecules/ion were measured for stainless steel vacuum chambers. The results obtained at LINAC3 are reviewed and their practical applications for the LEIR vacuum system are described. During heavy ion operation alarmingly large pressure rises were also reported from GSI and RHIC, their observations will be summarized. For the 2003 SPS heavy ion run (with indium beam) a desorption experiment at the CERN SPS is proposed by the Vacuum Group. The experimental setup is briefly described.