IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Vacuum Science & Technology Wednesday Sessions
       Session VST-WeA

Paper VST-WeA9
Experimental Investigation of Impact-induced Molecular Desorption by 4.2 MeV/amu Pb Ions

Wednesday, October 31, 2001, 4:40 pm, Room 125

Session: Gas Sorption Phenomena II
Presenter: E. Mahner, CERN, Switzerland
Authors: M. Chanel, CERN, Switzerland
J. Hansen, CERN, Switzerland
J.-M. Laurent, CERN, Switzerland
N. Madsen, CERN, Switzerland
E. Mahner, CERN, Switzerland
Correspondent: Click to Email
In preparation for the heavy ion program of the LHC, accumulation and cooling tests with lead ion beams have been performed in the LEAR storage ring. These tests have revealed that due to the unexpected large outgassing of the vacuum system, the dynamic pressure of the ring could not be maintained low enough to reach the required beam intensities. To determine the actions necessary to lower the dynamic pressure rise an experimental program has been initiated for measuring the molecular desorption yields of stainless steel vacuum chambers by the impact of 4.2 MeV/amu lead ions with the charge states +27 and +53. The test chambers were exposed either at grazing or at perpendicular incidence. Different surface treatments are reported in terms of the molecular desorption yields for H@sub 2@, CH@sub 4@, CO and CO@sub 2@. Unexpected large values of molecular yields per incident ion up to 10@super 4@ molecules/ion have been observed. The implications of these results for the vacuum system of the future ion accumulator ring (LEIR) and possible remedies to reduce the vacuum degradation will be discussed.