Paper VT-TuP2
Vacuum Pressure Simulation for the Insertion Device Beamline at X-Ray Ring of NSLS

Tuesday, November 10, 2009, 6:00 pm, Room Hall 3

Beamline 9 at the X-ray storage ring of the Brookhaven Lab’s National Synchrotron Light Source has been upgraded from a conventional bending magnet beamline to an insertion device beamline, with installation of a mini gap undulator (MGU) between the two RF cavities at upstream of dipole magnet. The new water-cooled undulator, which is made of neodymium-iron-boron magnet and vanadium-permandur poles, was tested to generate a high-brightness coherent 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). To meet required ultra-high vacuum (UHV) for beam transport under minimum scattering and aberration, the X-9 front-end was also upgraded, with installation of following provisions: fixed-aperture photon mask for beam filtering, high-density safety shutter for bremsstrahlung shielding, water-cooled collimator for ray focusing, windowless differential ion pump for shockwave throttling and spectrum broadening (2-20 keV), and pneumatically closed and sealed gate valve for the front-end vacuum and beamline vacuum separation. At downstream of the front-end gate valve, the 6-meter long X-9 is constructed of UHV-compatible SS spool pieces, welded bellows, optical chambers, fast shutter and angle valves. To maintain the intensity and quality of undulator beam for high-resolution sampling of nano materials, the conductance-limited beamline is equipped with multiple high-capacity ion pumps, respectively mounted at cryo-ready monochromator container (dual 300 l/s pumps), XZ-staged mirror tank (one 500 l/s) and exit-slit housing (one 300 l/s). For vacuum pressure minimization, the Monte-Carlo based Molflow code was used to simulate inline assemblies and pumping units encompassing the beam chamber, and the finite-difference based Vaccalc program was used to calculate pressure distribution along the beam trajectory, starting from the photon source MGU down to the beamline end valve next to the enclosure wall. Details of calculated pressure profile versus pumping setup will be presented. (Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886)