GSITemplate2007 GSI-UPGRADE-ACC-09 GSI SCIENTIFIC REPORT 2009 Status of the SIS 18 Vacuum Upgrade*


In the context of the technical developments for the construction of the Facility for Antiproton and Ion Research at GSI, an intensive programme for the vacuum upgrade of the existing heavy ion synchrotron (SIS 18) was started in 2005, with the aim to improve the beam lifetime and the beam intensity. To reach these purposes the installation of NEG coated dipole and quadrupole chambers was foreseen, and additionally to overcome the dynamic vacuum instability a collimation system equipped with thin film coated absorbers was designed and commissioned. The production of the thin film getter was carried out in two cylindrical magnetron sputtering facilities described in details in Ref. [1]. The surface chemical composition and the good activation behaviour of the produced thin films ( ≈ 1µm thick) were proved at CERN and at the Magdeburg University by X-ray Photoelectron Spectroscopy (XPS). Considering that the vacuum chambers mounted in accelerators undergo several ventingactivation cycles, a deep investigation on the NEG ageing was performed last year at GSI by Elastic Recoil Detection Analysis (ERDA) [2]. In each activation cycle an identical quantity of oxygen is dissolved in the film bulk. However heating at temperatures lower than 250°C (as performed for the GSI coated chambers) does not allow a uniform oxygen concentration to be reached in the film and, as a consequence, oxygen atoms are settled in the film to form a concentration profile with the maximum close to the surface (see fig.1) which finally leads to accelerated performance degradation. The film degradation can be also explained in terms of C accumulation on the surface; in effect this element needs a higher heating temperature to be dissolved in the film bulk [3]. An abrupt reduction of the pumping speed was observed for thin coatings (0.25µm) after about 12 cycles when heating at 200°C [4]. Figure 1: The number of activation cycle is plotted fro

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