The Extruded Aluminum Chamber…

1. The Extruded Aluminum Chamber…

2. Why the Aluminum Extrusion… • Relatively fast and inexpensive • We have experience • Built more than than 40 extruded aluminum insertion device chambers used at APS • Built extruded aluminum insertion device chambers in use around the world • Bessy II, SLS, CLS, Desy TTF • Minimal welding needed • Only a small, simple TIG weld on each end to attach a bi-metal flange • Aluminum surface provides high AC conductivity • Magnetic permeability of the chamber not a problem • No need for surface coating

3. The disadvantages… • The as-extruded aperture is not smooth enough to minimize wakefield effects. • The aperture must be polished to reduce Wakefield effects. • New methods of polishing had to be explored to reach an acceptable surface finish. • We have settled on an approach utilizing “abrasive flow machining” technology.

4. Abrasive Flow Polishing… • Normally an abrasive media is pushed back and forth through a part through the use of a hydraulic ram. • Our extrusion is greater than 10x longer than they are used to pushing through. • A custom built diverter directs the media out orthogonal to the hydraulic ram. • A flange attaches our extrusion with the diverter, and the media then flows out through our extrusion and drops into a bucket. • After some refinements, the process produces satisfactory results.

5. Best test results compared to the acceptability table… • The average rms slope error of the internal aperture in both the X (transverse) and Z (longitudinal) directions should ideally fall within the green or yellow sections of the acceptability table. • The green, yellow, orange and red symbols on the chart on the right are from the acceptability table. • Green is very desirable. • Yellow is acceptable. • Orange is not desirable. • Red should be avoided. • The blue diamonds are our data points. The red circle is the average of our data points—within the realm of acceptability.

6. Prototypes were built… • To test the viability and mechanical characteristics of the full length chamber we had two prototype chambers produced. • Both chambers were cleaned, baked, vacuum tested and mechanically measured. • The results were excellent.

7. Prototype 1 Results After a learning curve, the chamber was able to be straightened to ±50µm. We did find that adjustment screws must be located every 10” over entire length to achieve desired straightness.

8. Prototype 1 Results, Cont’d The chamber wall thickness fell within ± 50 µm. There was no appreciable change in chamber thickness within the accuracy of measurement between atmosphere and vacuum measurements. The calculated aperture height range = 50 µm.

9. Prototype 2 Results • The chamber was straightened to ±80 µm within 4 hours. • Could get within ±50 µm or better with minimal added effort.

10. Prototype 2 Results, Cont’d The chamber wall thickness fell within ± 50 µm. There was no appreciable change in chamber thickness within the accuracy of measurements between the atmosphere and the vacuum measurements. The calculated aperture height range = 80 µm.

11. Gap Tolerance Stack-up… • Chambers can be manufactured well within the specified thickness tolerance. • Chambers can be installed within the 250 µm tolerance allocated for chamber thickness variation and installation error using a reasonable amount of effort and modified support system. • The allocation should be switched so manufacturing tolerance is smaller and alignment tolerance is larger.

12. Vacuum Chamber Specifications • A draft Engineering Specification Document (ESD) is written. Requirements are below.

13. Prototype Vacuum Tests… • Neither Prototype Chamber had detectable leaks present with a sensitivity of better than 2.0 x10-10 mbar.l/sec • Pumping from only one end, with the gauges on the opposite end of the chamber, the ultimate pressure of the first prototype chamber was 4.7 x 10-7 torr. • Pumping from only one end, with the gauges on the opposite end of the chamber, the ultimate pressure of the second prototype chamber was 1.2 x 10-7 torr. • Therefore the average pressure within both was better than 5.0 x10-7 torr.

14. Prototype Vacuum Tests… • Separate tests were conducted on a piece of the polished extrusion in parallel with the mechanical tests on the unpolished prototype chambers • Polishing process introduced no contaminants that could not be removed by standard cleaning

15. Outgassing test results of the polished piece… • Pressure after baking was 7.9 x 10-9 torr • Residual outgassing is calculated at 2.4 x 10-13 torr.l/cm2.sec • Comparable to unpolished extrusion • RGA scans were also comparable to the unpolished prototypes

16. Other efforts continue… • The ESD is in review • The SOW for machining is signed off and part of the requisition • We have requested budgetary estimates for machining and begun writing requisitions • We have begun preparing our fabrication facility specifically for the LCLS chambers • Shipping crates have been ordered

17. The Schedule…

18. The Cost… So far Extrusion costs are within original (WAG) estimates + contingency factor

19. Progress to Date… • All Extrusions prepared for polishing and sent to Engineered Finishing Corporation (EFC) • Ends of extrusions are already machined to accept mating flange • Control samples of the first 54 un-polished extrusions were cut and sent for surface finish analysis • Polishing requisition awarded and polishing has begun • Polishing process is ongoing • 10 Chambers already partially polished