1 MONTECARLO CALCULATIONS OF PRESSURE PROFILES FOR THE ESRF DIPOLE/CROTCH AREA R. Kersevan – Vacuum Group, Tech.Serv.Division, ESRF, Grenoble ALBA-MaxLab Workshop on Vacuum Systems for Synchrotron Radiation Light Sources, Barcelona, Sept 2005

2 Motivation: Among many other things, during the summer 2005 shutdown (Aug 2005), the vacuum group has carried out… Vertical re-alignment (-2 mm vertical displacement, no venting) of all 64 crotch absorbers in the machine, following the failure (water leak) of one of them 1,2 First time in years that such a global intervention was carried out One crotch has been removed and replaced with a brand new one (cell vented) Synchrotron radiation-induced dynamic pressure rise seen in all 32 cells MC simulations done in order to get an estimate of the outgassing yield of each crotch  Work in progress…  (1) “Post Mortem Analysis of Cell-15’s Crotch Absorber Water Leak Failure”, R. Kersevan, this workshop (2) “”Identifying Vacuum Problems and the Recovery from Failures”, D. Schmied, this workshop

3 ESRF: STANDARD CELL IP/NEG DISTRIBUTION AND LOCATION OF VACUUM GAUGES: Ion pumps (Varian): ID:120 l/s ; CV4/CV11: 120 l/s; CV3/CV10/CV15: 45 l/s; dipoles: 60 l/s ; crotches: 400 l/s NEG pumps (SAES): crotches: GP500 ; elsewhere: GP200 PEN1 PEN3 RGA PEN4 PEN5 PEN6 PEN7 RGA ~5000 mm CELL LENGTH: 844 / 32 = 26.4 m

4 Global Vacuum Conditioning after Re-Start: Beam lifetime lower than usual (~ hours less) at beginning of USM End of machine-dedicated time: X-ray beam to users

5 Local Vacuum Conditioning after Re-Start: Cell 6: replacement of crotch-2; re-alignment of crotch-1 (-2 mm V); new CV3 chamber (precedes dipole-1); partially pre-conditioned NEG-coated, extruded Al CV5073 (not shown) PEN4: CV4 ; PEN5: CROTCH-1 ; PEN6: CV11 ; PEN7: CROTCH-2

6 X-rays from preceding dipole (430W) X-rays from this dipole (7200W) TOP-VIEW CROTCH-2 AND CV13 GEOMETRY: Total 5.82E+18 ph/s (46mrad) to FE absorber PEN7 location

7 DIPOLE-2 (CV12) GEOMETRY: radius of curvature: m Pumping-port geometry simulated separately

8 400 l/s SIP + GP500 NEG: simulated total pumping speeds of 500, 750, 1000 l/s PEN7 crotch absorber Closer view of the Molflow simulation model: total number of points: 339; total number of facets: 131 computation time: ~15 hours pressure test facet: 320x20mm 2

9 GP200 Pumping Port 60 l/s SIP Pumping Port PEN7 (star symbols) 400 l/s + GP500

10 A B sticking coefficient: s=1.0  913 l/s s=  60 l/s beam chamber: molecules are generated here ESRF DIPOLE PUMPING PORT GEOMETRY MODELED AND SIMULATED WITH MOLFLOW : C D 320 mm 280 mm C PPORT

11 AB The effective pumping speed is calculated via S eff = 1 / pressure test facet sticky surface (pump) C PPORT

12 The effective pumping speed is calculated via Seff = 1 / Statistical error proportional to 1/SQRT(molecules generated) C PPORT

13 Estimation of Gas Load Q: Photon Flux F: 46 mrad of dipole radiation correspond to ~5.82E+18 ph/s/200mA (ε ph >10 eV) Outgassing load: Q = F*k*  = 0.236*  mbar*l/s with k=4.05E-20 mbar*l/mol  =SR-induced outgassing yield (mol/ph) Substituting into the graph seen before, assuming the case 1000, 60, 200 l/s, and comparing with P meas =4.0E-7 mbar D=0.1 A*hr  ~5.5E+22 ph/m), one gets:  = 3.2E-4 mol/ph

14 Effect of Switching On/Off the IP: switching off the 400 l/s IP and looking at the effect on pressure at PEN7. Pressure increases ~1.7x (1.4E-9  2.4E-9) Ratio of PEN7 for the two cases (1000,60,200) and (500,60,200) is: 2.25 / 1.38 = 1.63

15 CONCLUSIONS: An example of use of the montecarlo code Molflow has been shown. The code has been used to evaluate… … the 3D geometry of ESRF dipole-crotch absorber vacuum chambers … the conductance of its two side pumping-ports … an estimate of the outgassing yield of the crotch absorber (obtained by comparing calculations with measured pressures) … a reasonable agreement of calculated vs measured pressure rise when the 400 l/s IP is switched off These preliminary results are encouraging, more to come soon… The contribution to this presentation from I.Parat, is acknowledged