Aperture and lifetime measurements with moveable scrapers at MAX II

Abstract

A set of measurement with moveable aperture restrictions, also called scrapers, has been carried out at MAX II (Nucl. Instr. and Meth. A 343 (1994) 644), the 1.5 GeV electron storage ring at MAX-lab, Lund, Sweden. The measurements with scrapers in MAX II have shown to give a number of useful results, such as the vertical and horizontal acceptance, which are 7.4×10 −6 and 9.6×10 −6 m, respectively, the lifetime limitations due to scattering on residual gas in the vacuum system, the Touschek effect and the quantum effect. The vertical acceptance of MAX II corresponds to a total vertical aperture of 10.04 mm and a total horizontal aperture of 22.4 mm at the position of the scraper, i.e. in the straight sections. The lifetime in MAX II at the measurement with 180 mA of stored beam at full energy, 1.5 GeV, was 23.8 h. The 23.8 h of lifetime is the total lifetime which is determined by the following lifetime limiting effects: Touschek effect 37 h, quantum effect ≫100 h, elastic scattering on the residual gas 134 h, and inelastic scattering on the residual gas 132 h. It has shown possible to inject into and ramp the MAX II storage ring with a total vertical aperture in the straight sections as small as 9.34 mm.The measurements have shown that it is possible to install an insertion device in MAX II with a 10 mm aperture without decreasing the beam lifetime, provided that the insertion devices do not deteriorate the vacuum situation. The gas mixture of the residual gas in the MAX II storage ring at operation has been measured and the absolute gas pressure is given by the results from the scraper measurements. In MAX II, as in most accelerators, the residual gas is dominated by hydrogen. The residual gas pressure in MAX II with 180 mA of stored beam at 1.5 GeV was 5.24×10 −9 Torr and it consists of 96.5% H 2, 1.1% H 2O, 1.8% CO, and 0.6% CO 2.