Paper VT-TuP10
Vacuum Pressure Simulation for the Upgrade of Front-End at NSLS Insertion Device Beamline

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

The beamline 9 at X-ray storage ring of the Brookhaven Lab’s National Synchrotron Light Source (NSLS) is being upgraded from a conventional bending magnet beamline to an insertion device beamline, with installation of a mini-gap undulator (MGU) at upstream of the dipole magnet. The new undulator, which is made of neodymium-iron-boron magnet and vanadium-permandur poles, will generate a high-brightness photon beam through the X-9 front-end to the experimental end-station enclosure, where sampling of nano materials will be conducted by small-angle X-ray scattering (SAXS). For the beam focusing and radiation shielding, most of the optical apparatus and vacuum systems at front-end of the beamline will be modified or replaced. To determine limit of conductance for gas pumping between the proposed aperture and collimator where the beam size is defined, vacuum pressure along the straight chamber from beam port of the undulator down to the differential pump (replacing beryllium window as vacuum barrier) is calculated, using two validated computer codes. In the statistical Molflow code which is a Monte-Carlo based software package, chamber conductance through different sections at front-end is estimated for pump arrangement. In the analytical Vaccalc code which is a finite-difference formulated Fortran program, pressure distribution along the beam axis is calculated based on balanced diffusion-and-pumping of gas species in consecutive segments of the vacuum chamber. The result is verified by the output from code runs previously performed to optimize the beamline vacuum. Details of pressure profile versus component setup at X-9 front-end will be presented. (Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886).