Gas scattering lifetime

Scattering of electrons on residual gas molecules also imposes serious lifetime restrictions: The cross section for electron losses after elastic scattering depends on the minimum transverse acceptance and on the vacuum conditions. With an insertion length of $\approx$2 m, $\beta_y=2.2$ m at entrance and exit as provided by the ``D2A'' optics of the SLS lattice is almost at optimum. Assuming 1 nTorr of carbon monoxide for the residual gas, the gas scattering lifetime obtained from the code ZAP [13] is 14 hrs for 4 mm insertion full gap height.