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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.
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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.
Contents • Requirements • Passive Pumping Design • Performance Analysis • Prototype Plan • Project Schedule • Conclusions
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
Use gas to attenuate below 2 keV Solid Attenuator Gas Attenuator Autocad Use Gas Use Solids * For a transmission of 10-4
Argon and Nitrogen for 104 Attenuation* * Based on NIST X-Ray Form Factor, Attenuation, Scattering Tables
Passive System Design Physical Variables Chamber Length (3-7.5 m) Overall Length (< 10 m) Aperture (3 mm – 5 mm) # of ports (4- 6)
Design Consideration – Critical Parameters • Chamber Length • Overall Length • Pumping (Turbo & Roughing L/s) • Chamber Pressure • Injected Gas (sccm) • Boundary Vacuum Pressure
Gas Attenuator Differential Pumping Configurations -Full Scale
10-m 6 port 3-mm Aperture 720 L/s Qi = 0 sccm Pump Down • Final outgassing rates of • 10-9 T-L/s-cm2 is assumed • Scroll Pump Speed vs Pressure • is modeled • Turbo Pump Speed vs Pressure • is modeled
Turbo Pumping Speed Modeling Scroll (Roughing) Pumping Speed Modeling
6 port 3-mm Aperture 720 L/s Qi = 5053 sccm Normal Operation with N2 Injection
6 port 3-mm Aperture 720 L/s Qi = 5053 sccm Normal Operation with N2 Injection 15.24 Torr 1.5x10-6 Torr
PrototypeGas Attenuator Differential Pumping - Passive 3-Port Objectives Configuration 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
System ConfigurationPhase-1 Gas Chamber Turbo Scroll Port 1,2,3
X-Ray Source Requirements • Within the range of 0.8 – 2 keV • Characteristic Beam • Collimated • Accessible (on site)
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
LLNL Vacuum Laboratory Building 132 S RM 1571
Vacuum Modeling- Pump Down • Final outgassing rates of • 10-9 T-L/s-cm2 is assumed • Scroll Pump Speed vs Pressure • is modeled • Turbo Pump Speed vs Pressure • is modeled
Prototype Testing Program • Facility Ready (132S RM 1571) • IWS Approved (IWS #12599) • Test Plan prepared • Engineering drawings being prepared • QA Plan prepared
Mass Flow Control 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)
Conclusions • Gas Attenuator preliminary design is near its completion • Prototype design completed and hardware procurement started • Project is on schedule