1. Stewart Shen shen2@llnl.gov October 27, 2005 1 LCLS-XTOD Gas Attenuator LCLS FAC Meeting October 27, 2005 Stewart Shen, Keith Kishiyama and Marty Roeben This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

2. Stewart Shen shen2@llnl.gov October 27, 2005 2 Contents Requirements Passive Pumping Design Performance Analysis Prototype Plan Project Schedule Conclusions

3. Stewart Shen shen2@llnl.gov October 27, 2005 3 Physics Requirements Be able to reduce the FEL beam intensity by up to 4 orders of magnitude at any energy within the design range (0.8 to 2 keV) Provide stable, reproducible (to within 1%) attenuation for repeated FEL shots. Implied Requirements Provide matched boundary vacuum conditions

4. Stewart Shen shen2@llnl.gov October 27, 2005 4 Use gas to attenuate below 2 keV Autocad Gas Attenuator Solid Attenuator Use Gas Use Solids * For a transmission of 10 -4

5. Stewart Shen shen2@llnl.gov October 27, 2005 5 Argon and Nitrogen for 10 4 Attenuation* * Based on NIST X-Ray Form Factor, Attenuation, Scattering Tables

6. Stewart Shen shen2@llnl.gov October 27, 2005 6 Nitrogen Pressure Requirements

7. Stewart Shen shen2@llnl.gov October 27, 2005 7 100-cm Design*

8. Stewart Shen shen2@llnl.gov October 27, 2005 8 Passive System Design Physical Variables Chamber Length (3-7.5 m) Overall Length (< 10 m) Aperture (3 mm – 5 mm) # of ports (4- 6)

9. Stewart Shen shen2@llnl.gov October 27, 2005 9 Chamber Length Overall Length Pumping (Turbo & Roughing L/s) Chamber Pressure Injected Gas (sccm) Boundary Vacuum Pressure Design Consideration – Critical Parameters

10. Stewart Shen shen2@llnl.gov October 27, 2005 10 Gas Attenuator Differential Pumping Configurations -Full Scale

11. Stewart Shen shen2@llnl.gov October 27, 2005 11 10-m 6 port 3-mm Aperture 720 L/s Qi = 0 sccm Pump Down Final outgassing rates of 10 -9 T-L/s-cm 2 is assumed Scroll Pump Speed vs Pressure is modeled Turbo Pump Speed vs Pressure is modeled

12. Stewart Shen shen2@llnl.gov October 27, 2005 12 Turbo Pumping Speed Modeling Scroll (Roughing) Pumping Speed Modeling

13. Stewart Shen shen2@llnl.gov October 27, 2005 13 6 port 3-mm Aperture 720 L/s Qi = 5053 sccm Normal Operation with N 2 Injection

14. Stewart Shen shen2@llnl.gov October 27, 2005 14 6 port 3-mm Aperture 720 L/s Qi = 5053 sccm Normal Operation with N 2 Injection 15.24 Torr 1.5x10 -6 Torr

15. Stewart Shen shen2@llnl.gov October 27, 2005 15 Prototype Gas Attenuator Differential Pumping - Passive 3-Port Configuration Objectives Phase 1 Demonstrate stable control of gas chamber pressure Validate the vacuum design for intermediate flow Verify mechanical & thermal stability Phase 2 (Optional) Demonstrate stable control of gas chamber pressure Calibrate the Ion Chamber Validate the intensity attenuation

16. Stewart Shen shen2@llnl.gov October 27, 2005 16 System Configuration Phase-1 Gas Chamber Port 1,2,3 Scroll Turbo

17. Stewart Shen shen2@llnl.gov October 27, 2005 17 X-Ray Source Requirements Within the range of 0.8 – 2 keV Characteristic Beam Collimated Accessible (on site)

18. Stewart Shen shen2@llnl.gov October 27, 2005 18 Soft X-Ray Source @ Bldg. 179 Technical Contact: Jim Emig (NTED) Max 10 kV with Be window (~1 mA) Available after October 05 Power Supply & Vacuum Control

19. Stewart Shen shen2@llnl.gov October 27, 2005 19 2 Views of System with X-ray Source Phase 2

20. Stewart Shen shen2@llnl.gov October 27, 2005 20

21. Stewart Shen shen2@llnl.gov October 27, 2005 21 LLNL Vacuum Laboratory Building 132 S RM 1571

22. Stewart Shen shen2@llnl.gov October 27, 2005 22 Prototype System Major Parameters

23. Stewart Shen shen2@llnl.gov October 27, 2005 23 Vacuum Modeling- Pump Down Final outgassing rates of 10 -9 T-L/s-cm 2 is assumed Scroll Pump Speed vs Pressure is modeled Turbo Pump Speed vs Pressure is modeled

24. Stewart Shen shen2@llnl.gov October 27, 2005 24 Vacuum Modeling- Gas Injection

25. Stewart Shen shen2@llnl.gov October 27, 2005 25 Vacuum Modeling- Normal Operation with injected N 2 gas

26. Stewart Shen shen2@llnl.gov October 27, 2005 26 Prototype Testing Program Facility Ready (132S RM 1571) IWS Approved (IWS #12599) Test Plan prepared Engineering drawings being prepared QA Plan prepared

27. Stewart Shen shen2@llnl.gov October 27, 2005 27 MKS Type 649 Electronic Pressure Controller Fully integrated baratron, mass flow meter, normally closed proportioning control valve and closed loop proportional/integral control electronics Flows to 5000 sccm Pressure control + 0.2% of full scale Time response – 1 sec (excluding system time constants) Mass Flow Control

28. Stewart Shen shen2@llnl.gov October 27, 2005 28 Gas Attenuator Design Schedule

29. Stewart Shen shen2@llnl.gov October 27, 2005 29 Gas Attenuator Procurement/Installation Schedule

30. Stewart Shen shen2@llnl.gov October 27, 2005 30

31. Stewart Shen shen2@llnl.gov October 27, 2005 31 Conclusions Gas Attenuator preliminary design is near its completion Prototype design completed and hardware procurement started Project is on schedule