1. LCLS XTOD Mechanical and Vacuum Systems; Gas Attenuator
Lehman Review
May 10-12, 2005
Pat Duffy, Mark McKernan, Donn McMahon, Stewart Shen, John Trent, Louann Tung

2. Outline Scope & Goals Systems Engineering – integrated plan
Mechanical and Vacuum System Development
Gas Attenuator Status
Summary

3. Scope and Goals
Mechanical & Vacuum Subsystems - This includes specification, design, and procurement pumps, pipes and stands for interconnecting the experimental tanks in the FEE, Near Hall, Tunnel and Far Hall.
Gas Attenuator - The gas attenuator is a device filled with gas whose purpose is to attenuate the FEL beam especially at low photon energies. The gases under consideration are N2, Ar and Xe at pressures up to 150 Torr. The gas attenuator must be windowless because of damage and absorption issues with the FEL beam. This means that gas will leak into the beam pipe and must be differentially pumped.

4. Minor Revised Planning Better Reflects our System Engineering Approach
High Level Plans remain unchanged
DOE Level 3 Milestones will remain unchanged
Current Cost Plan will remain unchanged
Staffing plan reflects plans & goals
Lead ME for Mechanical, Vacuum, and Gas Attenuators
Vacuum systems modeling and instrumentation & control experts
Lead designer – configuration drawings and staffing detailed design
Revised approach emphasizes concurrent development of Mechanical/Vacuum systems and XTOD instrumentation
Stretch FEE Mechanical & Vacuum design completion date
Advance instrumentation development schedules
Development starts with Beam Dump and progresses down beamline

5. Configuration Drawings are Critical to Tracking Design Progress and Changes
Treaty Flange
Muon Shield
Fast Valve
Slit B
PPS
Gas Attenuator
Fixed Mask
Slit A
Solid Attenuator
WFOV Camera

6. Baseline and Revised Plans
Stretch FEE Completion
Date but add to it
WBS
Title
Need
Baseline FY05 Plans
Revised FY05 Plans
1.5.2
Controls
Comiss
Specify & Cost
same
1.5.3
Mechanical & Vacuum
FEE Prelim Eng
BD/FEE, NEH, Tunnel, FEH Prelim Eng
Fixed mask
Facility
Calc Backgrounds
Prelim Eng
Slits
Gas attenuator
Prelim Eng, Proto & Simulation
Solid attenuator
Far Hall monochromater
Users
Far Hall pulse split and delay
Prototype
Modeling and simulation
Instrument Sim
Direct Imager
Detailed Eng Proto & Sim
Indirect Imager
Simulation, R&D
Total energy measurement
Proto & Sim
Spectrometer(s)
Flipper Mirror
Advanced design faster starting in FY05

7. The Overall Cost Plan for the Baseline Design will Remain Unaltered
PROJECT WBS[5]
FY05
FY06
FY07
FY08
FY09
Cumulative
Mech/Vac Front End
146,025
96,467
225,718
527,936
996,146
NEH Hutch 1
119,554
142,001
261,555
NEH Hutch 2
64,781
132,788
197,569
NEH Hutch 3
127,741
192,522
Mech/Vac Tunnel
42,833
2,061,857
2,104,690
FEH Hutch 1
32,049
108,829
140,877
FEH Hutch 2
114,728
146,777
FEH Hutch 3
69,553
101,601
Fixed Mask
254,605
94,903
349,508
Slit/Collimator A
1,090,360
960,139
2,050,499
Slit/Collimator B
1,030,057
Gas Attenuator
404,996
565,148
1,385,774
2,355,917

8. LCLS XTOD Mechanical & Vacuum Systems Development

9. Mechanical and Vacuum Systems Development Plan
Baseline requirements are being refined
Beam dump area is undergoing revision
Incorporation of a FEE low pass mirror is being tracked
XTOD Interfaces are being defined (Beam dump, XES, Conventional Facilities, Controls)
ICDs are being written
Control conventions, operational & safety strategies are being formed
Detailed designs are under development
Baseline supporting structures (pumps, pipes, tanks)
Resulting requirements and interfaces for vacuum systems are being refined
Seismic design, Vibration analysis
Detailed vacuum modeling and instrumentation & controls
Revised mechanical & vacuum cost estimates

10. Pump Stand with Pipe and
Detailed Seismic And Vibration Analyses will be Conducted for all Structural Components
Seismic Design:
Seismic model is based on components chosen by initial vacuum analyses
Baseline design for pump stands and flex supports meet LLNL and SLAC Seismic Design Standards
Anchoring for baseline supports are chosen (HILTI Kwik Bolt 3)
Vibration Analyses
SLAC typical input spectra required
Vibration mode requirements TBD
Pump Stand with Pipe and
Flex Supports

11. The Proposed FEE Mirror Design will Impact XTOD Planning, Cost and Schedule
Instrumentation space will be limited
May require potential dual use diagnostic tanks
Potential impact on the Gas Attenuator design
Two design options available
May dictate smaller form factor design
Cost and schedule impact still needs to be done
Beam Dump XTOD
Instrumentation
Proposed Low Pass
Mirror System
FEE XTOD
Instrumentation

12. Pressure History at Any Location is Calculated With Our Custom Vacuum Model
Model uses Mathematica to solve for pressure using N coupled differential equations for roughing, turbo, and ion pumps
Vi dPi/dt =  Qin -  Qout for i = 1, N where N = total volume elements
Qin = time-dependent outgassing into volume i
Qout = Cij (Pi-Pj)
where Cij is the conductance into adjacent volume j
or Qout = Sp Pi and Sp is the pressure dependent pump speed
Input local outgassing history that depends on material and
handling procedures for each component
Use curve fit to pump speed curves as supplied by vendor
Can also model effects of pump failure on pressure at any location
These capabilities allow one to optimally choose the number and size of vacuum pumps for any system
This method was used to model an rf linac (where N=200) and actual hardware tests confirmed the model’s predictions (Spallation Neutron Source at LANL)

13. Pressure history at ends of 40 ft, 4” OD tube with pump in the middle
Assume outgassing rate of
10-10 T-l/sec/cm2 is reached in 100 hrs.
Pressure scales with outgassing rate so
the model accuracy is only as good
as the outgassing rates that are input.
100 1
10-2
10-8
10-6
10-4
Torr
102
103
104
105
seconds
300 L/min rough
on for 30 min
70 L/s Turbo on
for 10 hours
75 L/s ion pump on
for remaining time
100 hrs
1.0 x 10-7 T

14. LCLS Gas Attenuator Project Status

15. Gas Attenuator Status Project Progress Design Concept Prototype
Resources, costs & schedule confirmed
Design Concept
“Rotating Aperture” scheme added
Passive Gas attenuator Modeled
Prototype
Scope and schedule being modified

16. Passive Pumping- Calculations for 6-Port configuration
Gas flow
to chamber
37.7 T-L/sec
2976 sccm
Pump Speed
6 x 50 L/s
Inter-connection
Coupling
L = 3 cm
Hole size = 3 mm dia.
6-port configuration can maintain 10 Torr with 3 mm apertures (GA Chamber Length = 6 m)

17. Another Option Neutron Imaging Rotating Aperture Configurations A Prototype Was Recently Successfully Tested
apertures
Gas cell
With apertures
motor
Major advantage is, by precisely gating the aperture opening synchronized with beam pulses, the amount of gas flow can be lowered by at least one order of magnitude
~ 1/(duty factor)
For NI application:
duty factor is 2%
two 5-mm 4000 rpm

18. Gas Attenuator with Rotating Aperture Configurations

19. * Based on NIST X-Ray Form Factor, Attenuation, Scattering Tables
100-cm Design with RA*
* Based on NIST X-Ray Form Factor, Attenuation, Scattering Tables

20. Nitrogen Pressure Requirements
Operation from 0 to 150 Torr has been modeled with reasonable pumping

21. LCLS GA/RA Model

22. LCLS GA/RA Calculation Results
Gas Attenuator set at 150 Torr
Cell 1 at 2.2 mTorr
Cell 2 at 3.76x 10-6 Torr
Pumping Condition
S2: one Scroll 600 L/m
one Turbo 300 L/s
S3: one Turbo 600 L/s
Qi: 7.5 T-L/s (592 sccm)

23. System Comparisons of GA Design Options internal moving components
Design Features
Passive Pumping
Space Constraint
Rotating Aperture
Length
10 m
<10 m
<4 m
Photon Energy Limits
Up to 2 KeV
Up to 3 KeV
Circulated N2 Gas
3000 sccm
> 3000 sccm
590 sccm
Number of vessels 7 7+ 5
Prototype
planned
demonstrated
Risk
low
moderate
internal moving components
Risk Management
may not need prototype
needs prototype
can be minimized by:
1. using commercial
components (air bearings)
2. long-term prototype testing
Control System
vacuum
vacuum and motor control synchronized with beam pulse

24. Summary of the Design with Rotating Aperture Scheme
Potential Benefits
Shorter length
Less gas circulation
May extend the photon energy level beyond 2 KeV
Potential Risks
Moving parts inside vessel, but the risk can be managed
Prototype for other LLNL program has been successfully tested
Simultaneous Design(s) in progress
Design revision of existing rotating aperture design for LCLS
“Optimization” of space constrained passive systems
Down selection of design options
Will be included in the Prototype Task

25. Summary
The XTOD Mechanical And Vacuum Systems will provide the infrastructure interconnecting the diagnostics and experimental tanks in the FEE, Near Hall, Tunnel and Far Hall
Mechanical requirements and interfaces are being refined with detailed design proceeding
Vacuum models are being vetted and detailed system models will follow
The XTOD Gas Attenuator has 2 design concepts
Design based upon an existing LLNL rotating aperturte design and a passive design
We will down select amongst these options
Minor schedule revision will permit a more integrated design process by starting key instrumentation designs earlier
XTOD mechanical team has staffed up for FY05
The detailed design work will escalate in FY-06 and FY-07
We are mindful of the FEE deflection mirror and its potential impact