1. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 1 LCLS Undulator Vacuum Chamber Dean R. Walters

2. drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 2 Contents Overview Prototype design Construction Issues String Test Beam Finder Wire Conclusion

3. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 3 Overview

4. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 4 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.

5. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 5 Single Compound Screw Set-up Six Compound Screws Set-up Two Compound Screws Set-up Fourteen Compound Screws Set- up, Full Chamber Mock-up

6. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 6 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 Permeability measurement results of 20Cb-3 (Alloy 20) at ANL Central Shops by SH Lee on 4/7/04 Plate: 1.010~1.012 – 19 mm thk (most points 1.010) Sheet: 1.004~1.006 – 1.5 mm thk (most points 1.005), after correcting for thickness the values are 1.008~1.012 with an average of 1.010.

7. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 7 Technical Challenges Polishing – surface roughness 100~200 nm Ra (#8 mirror-finished), securing 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 0.01-10 mm period range. Structures with periods shorter than 10 µm will be kept smaller at amplitude of less than 25 nm. Forming – U Channel Bending The surface in the area of the bend is roughen like an orange peel Tooling design (die/punch) for 12-ft-long forming Welding Reduction of weld distortion to within straightness tolerance 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) Controlling the distortion in the XZ plane Al-coating – thickness/uniformity Ability to perform coating in a small aperture chamber

8. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 8 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.

9. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 9 Surface Roughness of Bent Samples 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 352 nm 207 nm 658 nm 871 nm

10. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 10 Surface Roughness of Bent Samples Bent sample (#) Spot location, object lens, field of view Sq(nm) (rms) Sa(nm) (avg) P-V (nm)PicturesRemarks 1 Curved area 50 x 0.244 mm 2 390292618510.5 mm thick 304 SST, R=1.5 210998671056021.5 mm thick 316 SST, R=1.5 3290217363330.5 mm thick 304 SST, R=2.5 4908720930641.5 mm thick 316 SST, R=2.5 1 Flat area 2.5 x 4.89 mm 2 89678450.5 mm thick 304 SST, R=1.5 2785912051.5 mm thick 316 SST, R=1.5 318013721370.5 mm thick 304 SST, R=2.5 436267521.5 mm thick 316 SST, R=2.5 1 Flat area 5 x 2.44 mm 2 6756143450.5 mm thick 304 SST, R=1.5 24229308861.5 mm thick 316 SST, R=1.5 37149564070.5 mm thick 304 SST, R=2.5 4261983681.5 mm thick 316 SST, R=2.5 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).

11. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 11 Criteria for Surface Roughness The wakefield tolerances are chosen such that the resistive wall wakefield dominates the other wakefield components, including surface roughness wakefields and geometric wakefields. acceptable The longitudinal impedance for a circular chamber cross section due to roughness is [1] [1] G.V. Stupakov, “Surface Roughness Impedance”, SLAC-PUB-8743 (2000) This is taken from: Undulator Vacuum Chamber Surface Roughness Measurements and Expected Wakefields Heinz-Dieter Nuhn, SLAC / LCLS Presented at Physics Meeting on April 13, 2006

12. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 12 Criteria for Surface Roughness Sample: #8 Mode: PM Size: 0.244 x 0.244 mm 2 Objective: 50x x’ rms : 1.0 mrad; z’ rms : 1.1 mrad x’ rms : 2.1 mrad; z’ rms : 2.2 mrad Size: 0.244 x 0.244 mm 2 x’ rms : 234 mrad; z’ rms : 425 mrad x’ rms : 221 mrad; z’ rms : 398 mrad Sample: #8 Mode: EX Objective: 50x Flat Sample Curved Sample x’ rms and z’ rms is a complementary means to express the aspect ratio. The method evaluates the height and the wavelength in terms of an angle that is express in mradians. In the initial calculations 10.5 mrad is considered acceptable for flat surfaces and 35 mrad for curved. With these results, work on reducing the roughness in the bend area is continuing. Besides the work to better cushion the polished surface from the bend dies there is also work on: (1) electro-polish after bending, (2) mechanical polish after bending, and (3) exploring the possibilities that the metallurgical condition of the base material can be altered to improve the surface finish.

13. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 13 Criteria for Surface Roughness 0 deg 90 deg Work on the criteria for surface roughness has made progress although there is still a need to extend it. The work shown in previous slides are for a circular cross section chamber whereas the cross section of this chamber design is obround. The curve at right shows the chamber radius in the first quadrant. Work needs to address the real chamber shape and the limits of practical metal polishing in this confined configuration. The specification needs to blend the full the allowance from the impedance plus taking into account the chamber shape.

14. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 14 E2L1.5R300 1 cm/s E2L2R250 1 cm/s E2L3R180 1 cm/s E3L1R400 1 cm/s 1.53 mm E2.5L2R250 0.8 cm/s E2.5L2R250 0.9 cm/s E2.5L2R250 1 cm/s E2.5L2R250 1.2 cm/s 1.53 mm Laser Weld Test – 316LN SST E2.5L2R250, 5 J/p, P = 1250W, 1 cm/s, Ar @ 60 scfh Energy per ms, E (J/ms) = 2~3, Pulse width, L (ms) = 1.5~3 Pulse repetition rate, R (Hz) =180~400.

15. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 15 Laser Welding Test Working with Laser Welding Company to perform welding They have made initial samples Below are examples of two weld joints Butt Weld with penetration ~2 mm Lap Weld with penetration ~2.5 mm

16. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 16 Welding Tasks 1. Work with vendor to determine weld joints and tooling requirements. 2. Design and construct weld tooling 3. Weld prototype chambers

17. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 17 Coating Coating Method Pulsed Sputter Coating of 99.99% Aluminum onto Stainless Steel substrate 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 even after extreme bending. Coating after Fabrication This insures coverage over all parts including the welds. Working with a consultant to work out the apparatus and method for applying the film

18. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 18 Center Aluminum tube that can be used for plasma cleaning and coating 1.Coating will now be performed after all the welding and machining are done. The coating tooling will be added to the bake out equipment 2.There are two motivations for revising the coating: 1.Available time on large area planar coating systems is difficult for this batch size, 4 sheets. 2.This solves the problem of coating the strongback and the area of the flange weld area. 3.Adhesion of film is not a strong factor in the characteristics the film. 4.Working with an outside consultant to define process and equipment. Revised Coating Method

19. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 19 Work Process of Chamber Prototypes

20. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 20 Prototype Construction Schedule Bid Process started in the first week of January for the chamber and the supports Quotes on the supports came in January, delivery in March Work is progressing for a later June 2006 completion

21. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 21 String Test Vacuum Test to simulate conductance of small aperture chambers

22. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 22 Beam Finder Wire Rendering of Design This is the mock-up for the SUT The BFW, support, and connection to ion pump are shown.

23. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 23 Beam Finder Wire Summation of Bench Test Test results reflect a +/- 5 micron repeatability and an adjustment resolution of +/- 2 micron.

24. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 24 Conclusions Chamber The chamber and supports designs have progressed to the point where they are ready for the construction of the prototype. The plan is to construct a two chambers. One where the U-Channel is made of 316LN stainless steel and the strong-back of 316 SST. The other made of 20Cb-3 (Alloy 20) stainless steel, this material can be purchased through domestic suppliers. Construction Polishing Vendor samples have been measured with surface finishes smoother than 25 nm on flat samples.. Bending Samples have been formed into a U shape and the surfaces of some of the samples are smoother than 400 nm. There are also examples that are rougher than what is allowable by the current physics criteria. The criteria will need to be expanded for the current chamber shape.

25. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 25 Conclusions Construction (continued) 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 2.0 mm. Work has begun with a laser welding shop and samples have produced penetrations up to 3 mm. Work with the vendor will determine the weld joints and tooling requirements Coating Aluminum has been sputtered onto stainless steel, that was plasma cleaned, and the strength of the adhesion was great enough to hold the film even on a flexible substrate. In order to produce a coating over all internal surfaces, the coating will now be done as a final step after the welding. An agreement is being worked for a consultant to aid in the definiation of sputtering process. Beam Finder Wire Results of the bench test show that the repeatability of placing the wire is ± 5 μm

26. Dean R. Walters drw@aps.anl.gov April 20, 2006 Vacuum Chamber Review 26 Any Questions? I would like to acknowledge the continuing efforts of: SH Lee, J Bailey, J Morgan, and DS Doran