1. A. Kraemer, OLAVIII, July 11th, 2011 1 Gas Loads into SIS100 Cryogenic Vacuum Sections A. Kraemer, Calculations and Transparencies courtesy of St. Wilfert GSI Helmholtz-Zentrum für Schwerionenforschung mbH Accelerator Department – Vacuum Systems Planckstraße 1 64291 Darmstadt GERMANY

2. A. Kraemer, OLAVIII, July 11th, 2011 2 Schematic Layout Vacuum System of SIS100 Total length of SIS100: 1083.6 m (82% cold, 18% warm) Required vacuum: ~10 -12 mbar 6-fold symmetry (six straights and six arcs) 25 warm sections (24x 8.3 m long, 1x 3.3 m) 25 cold sections (6 long arcs (5x 135m 1x 122.6m), 19 short straight, 18x 4.3m, 1x 9.2m) 50 Cold/Warm-Transitions for beam vacuum 50 gate valves

3. A. Kraemer, OLAVIII, July 11th, 2011 3 Vacuum Sectorization SIS100 One Superperiod (out of six) Length of superperiod 180.6m (from A to B) 4 warm sections (each about 8.3m long) 4 cold sections (1 long arcs 135m, 3 short straight 4.3m) 8 Cold/Warm-Transitions 8 gate valves one roughing station per short cold section in the straights, six roughing stations in the arc 13 adsorption pumps to provide pumping speed for H 2 and He in the cold sections. No vacuum barriers in isolation vacuum

4. A. Kraemer, OLAVIII, July 11th, 2011 4 Cryo Adsorption Pumps  auxiliary pumps are used primarily to lower the partial pressures of H 2 and He  10 cryosorption pumps per arc (each 13 m) and one per short quadrupole doublet in the straight sections  consists of several round cryopanels (i.e. copper disks coated with charcoal (SC2 type; Chemviron) coating by KIT, Karlsruhe, Germany)  panels stacked on a central cooling tube cooled down to T ~ 4.5K

5. A. Kraemer, OLAVIII, July 11th, 2011 5 The basics of HOBSON-WELCH model theoretical model for calculating pressure profiles in a cryogenically cooled vacuum tube with wall-pumping and induced external H 2 or He gas loads (e.g. leaks) predicts that a localized H 2 or He gas flux into a sticky cold- bore tube generates a wave-like pressure gradient whose wave- front can be considered as moving cryosorption pump the wave-front propagates rather slowly through the tube wave-front propagation depends on leak rate, gas species, dimensions and surface roughness of the cold- bore tube validity of model was experimentally confirmed in several empirical studies Hobson, J. P.; Welch, K. M.: Time-dependent Helium and Hydrogen Pressure Profiles in a Long, Cryogenically Cooled Tube, Pumped at Periodic Intervals, J. Vac. Sci. Technol. A 11(4) (1993), 1566

6. A. Kraemer, OLAVIII, July 11th, 2011 6 The basics of HOBSON-WELCH model HOBSON & WELCH (1993) for circular tubes: WILFERT (2011) for elliptical tubes: Wallén, E.: Adsorption Isotherms of He and H 2 at Liquid He Temperatures J. Vac. Sci. Technol. A 15(2) (1997), 265 Q leak rate, t time k tube geometry factor, Θ(x) relative surface coverage => known from adsorption isotherm

7. A. Kraemer, OLAVIII, July 11th, 2011 7 Gas Flow into SIS100 Cryogenic Arc 2) H 2 gas load from room temperature operated vacuum sections 2Q ≈ 7.1 x 10 -9 mbar ℓ s -1 (T = 4.5K) from each roughing CWT! (high gas load!) 1) H 2 gas load from the Cold/warm- transition for rough pumping Q ≈ 10 -11 mbar ℓ s -1 (T = 4.5K) from baked RT vacuum sections (=> can be neglected) Adsorption Pumps 13m

8. A. Kraemer, OLAVIII, July 11th, 2011 8 Theoretical Pressure Increase in cryogenic SIS100 arc

9. A. Kraemer, OLAVIII, July 11th, 2011 9 Theoretical Pressure Increase in SIS100 cryogenic arc With assumed outgassing rate of unbaked stainless steel pressure increase is to high!  Solution: bakeout of roughing pumping ports?

10. A. Kraemer, OLAVIII, July 11th, 2011 10 Questions Is our model applicable? Was the Hobson-Welch model verified for Hydrogen? Are there experimental adsorption isothermes for temperatures 4.2K < T < 20K Is there a model for inhomogeneous temperature distributions along the chamber? How is this problem solved in other labs?

11. A. Kraemer, OLAVIII, July 11th, 2011 11 Gas Flow through the Cryogenic Vacuum Tube

12. A. Kraemer, OLAVIII, July 11th, 2011 12