National Synchrotron Light Source II (NSLS-II) will be a 3-GeV, 792-meter circumference, 3rd generation synchrotron radiation facility, with ultra low emittance electron beams and extremely high brightness X-ray beams. The storage ring vacuum system has a simulated average operating pressure of less than 1x10-9 mbar. A summary of the updated vacuum system design will be presented, based on outcome from pressure simulation using window-version Monte-Carlo based MOLFLOW+ code. The versatile PC-compatible code provides increasing details in pressure distribution of residual gases in the vacuum system, particularly for those active species scattering at innards of high-power and small-gap insertion devices. Since low emittance for electron beam is expected to achieve when proposed damping wigglers are installed at storage ring, a fine segmentation of code input at such critical sections will be processed to evaluate details from calculated pressure profile.

 

*Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886