1. LCLS Undulator Vacuum Chamber
Dean R. Walters

2. Contents Overview Conceptual design Construction Issues Schedule
Undulator vacuum chamber
Support assembly
Adjustment mechanism
Materials
Construction Issues
Polishing
Forming
Welding
Coating
Schedule
Conclusion

3. Total undulator length (x11): 131.52 m
Overview
Undulator
3,400
470
898
12,038 mm
Total undulator length (x11): m
Beam Position Monitor
Beam Finger Wire
Future Diagnostics Suite
Quadrupoles
Fabrication plan for vacuum chamber:
33 production vacuum chambers & 7 spares
1 mock-up chamber for single undulator test
1 vacuum chamber for prototype

4. Contents Overview Conceptual design Construction Issues Schedule
Undulator vacuum chamber
Support assembly
Adjustment mechanism
Materials
Construction Issues
Polishing
Forming
Welding
Coating
Schedule
Conclusion

5. Vacuum Chamber Assembly
Compound screws (SST/Brass or others)
NW 50 Flange -Clamp Type (316L SST)
Vacuum Chamber (316LN SST)
U-profile Al-coated SST
Chamber Strong-back
Laser Welding

6. LCLS Vacuum Chamber Ass’y
Vacuum Chamber Assembly
Support Assembly
X-Adjustor
Z-Adjustor

7. Prototype Vacuum Chamber Assembly
Results of the Internal Design Review of the Chamber Assembly (Jan. 5, 2006)
The committee was charged with reviewing the design so that construction of the prototype could start.
The conclusions of the committee were that the design and the construction method were thought out enough to support the building of the prototype.

8. Permeability of Stainless Steels
Magnetic Measurements
from “Magnetic Properties of Undulator Vacuum Chamber Materials for the Linac Coherent Light Source” by SH Lee presented at FEL2005

9. Design on track to complete on schedule
Prototype Design
Internal Design Reviewed occurred January 5, 2006 covering the chamber, supports, and the bellows.
Internal Design Reviewed occurred January 5, 2006 covering the chamber, supports, and the bellows.
Design on track to complete on schedule

10. Contents Overview Conceptual design Construction Issues Schedule
Undulator vacuum chamber
Support assembly
Adjustment mechanism
Materials
Construction Issues
Polishing
Forming
Welding
Coating
Schedule
Conclusion

11. Manufacturing Processes
SST Plate (144” x 6” x 1”)
Laser Welding
Milling/Grinding
Forming
Al-Coating
Milling/Polishing
SST Sheet (144” x 2” x 0.118”)
Polishing/Grinding

12. Technical Challenges Polishing – surface roughness
100~200 nm Ra (#8 mirror-finished)
The physics specification is: For each spatial frequency component of the surface roughness, the ratio of the corresponding spatial wavelength to the amplitude will be greater or equal to 300 over the mm period range. Structures with periods shorter than 10 µm will be kept smaller at amplitude of less than 25 nm.
Al-coating – thickness/uniformity
A layer of 100 ~150 nm
Forming – flatness/spring-back
Any damages on Inner surfaces
Flatness due to spring-back
Tooling design (die/punch) for 12-ft-long forming
Welding – penetration depth/heat-affected-zone
Laser welding/E-Beam welding for less weld distortion and leak tight
Tooling design (welding head motion control) for 12-ft-long weld
Final machining of chamber weldment
Wall thickness of 0.5 mm (grinding/milling) – waviness / uniformity
Geometric tolerance of flat surface ( 100 m)
Straightness of the strong-back plate (200 m)
Vertical adjustment mechanism for installation and alignment
Compound screw mechanism works fine or another option

13. Polishing of Stainless Steel
ANL bought samples of stainless steel sheets from Pacific Plus of Dallas, TX.
Pacific Plus specifies the surface to be 1 µin Ra (25 nm Ra).
Samples of 1.5 mm thick 316 SST sheets (1 ft x ft) and 0.5 mm thick 304 SST sheet (4 ft x 8 ft) were bought to evaluate the impact of manufacturing operation on the surface finish.
Samples for the Bending test were made from this material.
Samples of polished stainless steel have procured from MPC Industries of Irvine, Ca.
These have a directional finish and will be measured at ANL in the near future.
Pacific Plus samples (1″ x 1″ ) were measured on a Tencor Alpha-Step to obtain a 2D surface profile. Results shown on following page
Recent samples were measured on an ADE RTS MicroXAM surface interferometer

14. Polishing of Stainless Steel
7/4/2019
Polishing of Stainless Steel
Samples 0.5 mm thick Type 304 Stainless Steel
Ra=207 Ǻ Ra=140 Ǻ (Sample is turned 90 deg)
Ra=147 Ǻ Ra=140 Ǻ
Samples 1.5 mm thick Type 316 Stainless Steel
Ra=1043 Ǻ Ra=149 Ǻ (Sample is turned 90 deg)
Ra=289 Ǻ Ra=97 Ǻ
White Graph is a 5 m filter (default) Green is a band-pass filter of 5 m & 0.8 mm
Test

15. Polishing of Stainless Steel
The APS owns a white light interferometer that will be used to surface map prototype and production samples. This will speed up the measurement of the samples

16. Bending of Stainless Steel
Object of Tests was to investigate any damages to surface area
With the bending tooling, sample parts were made
V-Block, full-radius, and 1.5 radius female dies – related male punches
To measure the roughness, bent samples were cut by wire-EDM
Also, flat samples were provided to compare the results
Measured by MicroXAM RTS surface profiler in the vertical scanning white light interferometry mode.

17. Surface Roughness of Bent Samples
Spot location, object lens, field of view
Sq(nm)
(rms)
Sa(nm)
(avg)
P-V (nm)
Pictures
Remarks 1
Curved area
50 x
0.244 mm2
390
292
6185
0.5 mm thick 304 SST, R=1.5 2
1099
867
10560
1.5 mm thick 316 SST, R=1.5 3
290
217
3633
0.5 mm thick 304 SST, R=2.5 4
908
720
9306
1.5 mm thick 316 SST, R=2.5
Flat area
2.5 x
4.89 mm2 89 67
845 78 59
1205
180
137
2137 36 26
752
5 x
2.44 mm2 56
1434 5 42 29
3088 6 71 49
5640 7 19
836 8
For each sample, the values shown are average of four measurements
Surface finishes with thinner sheets (0.5 mm) showed better than thicker sheets(1.5 mm).
Surface finishes with large bent radius (R=2.5 mm) showed better than small bent radius (R=1.5mm).

18. Laser Welding Test
Welding tests were conducted using ANL equipments in developing weld parameters.
Beads On Plate (BOP) to see penetration depth
Size: 1˝ x 3˝ x 1/16˝
1,600 W pulsed Nd:YAG Laser
Max. average power: 1,600 W
Max. peak power: 64 kW
Pulse repetition rate  800 Hz
Pulse width: 0.1~ 10 ms
The Laser Laboratory has greater expertise than the local vendor.
The Lab has the ability to monitor the weld conditions in real time.
Monitoring DC/AC signals
DC signal - penetration depth
AC signal – welding defects like humping and undercut/spatters
This laser has the ability to penetrate up to 4 mm
The 1.6 kW pulsed Nd:YAG laser

19. Laser Weld Test – 316LN SST
E2L1.5R300
1 cm/s
E2L2R250
E2L3R180
E3L1R400
1.53 mm
E2.5L2R250
0.8 cm/s
0.9 cm/s
1 cm/s
1.2 cm/s
1.53 mm
E2.5L2R250, 5 J/p, P = 1250W, 1 cm/s, 60 scfh
Energy per ms, E (J/ms) = 2~3, Pulse width, L (ms) = 1.5~3 Pulse repetition rate, R (Hz) =180~400.

20. Laser Welding Test
Laser welding parameters are developed for full penetration greater than 0.8 mm with three austenite stainless steels (304,316LN, 20Cb-3). The parameters are:
Laser energy per ms, E: 2.5  E < 4 J/ms
Laser average power: – 1000 W
Laser pulse repetition rate, R: 160  E  400 Hz
Laser pulse width, L: 1  L  2 ms
Beam travel speed: ~1.75 cm/s
Cover gas: 60 scfh, leading configuration
Focusing beam: mm at surface
316LN has better weldibility than 20Cb-3 in terms of laser weld.
Weld defects such as humping, undercut, drop-out, and pores are found in the welds when the laser parameters were not at the optimal settings.
Most of the porosities were found in 20Cb-3 welds made at 2.5 J/ms. Increasing the laser energy to 3 J/ms reduced or eliminated the porosity. Required more study on longitudinal sections to verify this conclusion.

21. Welding Tasks
Tooling is lagging at this point, but it is expected to catch up now that the weld development is done and the process is better understood

22. Coating Coating Method Results of Adhesion Tests
7/4/2019
Coating
Coating Method
Pulsed Sputter Coating of Aluminum onto Stainless Steel substrate
Target purity of 99.99% Aluminum
Substrates are plasma cleaned in Ar prior to coating
Results of Adhesion Tests
Used Scotch Tape to determine adhesion of film to substrate
Unable to detach film from substrate immediately after coating in system.
Unable to detach film from substrate after heating sample in vacuum oven to 450oC.
Test

23. Prototype Construction Schedule
Bid Process started in the first week of January for the chamber and the supports
Quotes on the supports came in started in January
Work is progressing for a later June 2006 completion

24. 7/4/2019
Conclusions
Chamber
The chamber and supports designs have progressed to the point where they are ready for the construction of the prototype.
The Design Review Committee agrees that the designs are ready for prototyping.
The plan is to construct a chamber made of 316LN stainless steel with an interior coating of aluminum.
Construction
Polishing
Vendor samples have been measured with surface finishes smoother than 25 nm.
Bending
Samples have been formed into a U shape and the surfaces of some of the samples are smoother than 400 nm.
Welding
A series of Laser weld tests have been completed and a set of welding parameters have been determined that can yield penetrations up to 1.5 mm.
Coating
Aluminum has been sputtered onto stainless steel and the strength of the adhesion passed the ‘scotch tape’ test after baking.
Schedule
Additional resources have been added to improve the rate of progress.
Schedules and effort is being reviewed to start production earlier than the current plan.
Test

25. Any Questions?