Status of 201 MHz Prototype Cavity and Curved Be Windows

1. Status of 201 MHz Prototype Cavity and Curved Be Windows Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory MICE Collaboration Meeting at CERN March 28 – April 1, 2004

2. Collaborators R. MacGill J. Staples, S. Virostek, M. Zisman Lawrence Berkeley National Laboratory, USA R. Rimmer, L. Philips, G. Wu Thomas Jefferson Laboratory, USA W. Lau, S. Yang Dept. of Physics, Oxford University, UK D. Summers, M. Reep Mississippi University, Oxford, MS, USA Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

3. The Cavity Design Update Cavity profile design was last updated last summer and with considerations of • Low ratio of acceleration field versus peak surface field (~ 1.04) • Numerical simulations with MAFIA, URMEL, SUPERFISH andANSYS (RF, thermal and mechanical) codes • Simple (easier) fabrication without losing the performance • Cavity is ready for e-beam welding at JLab now • De-mountable window design allow for other windows and grids • Baseline window design: curved thin(ner) Be windows (S. Yang’s talk) • Four larger (~4”) ports will be extruded: two for loop couplers, one for vacuum and one extra • Two smaller ports for probes • Mechanical tuners similar to the ones used in SCRF cavities, and will be developed very soon The cavity will be ready for high power test this fall Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

4. Brief Review: Cavity Concept Extruding ports Spinning of half shells and e-beam welding Water cooling channels Cavity design accommodates different windows Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

5. The Cavity Profile update Spherical section at the equator to ease addition of ports (± ~ 6o) Elliptical-like (two circles) nose to reduce peak surface field Stiffener ring 2o tilt angle 6-mm Cu sheet allows for uses of spinning technique and mechanical tuners De-mountable Pre-curved Be windows to terminate RF fields at the iris Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

6. The Cavity Profile update (cont’d) • RF/Coupling coil module layout • Details of the cavity profile • Ports for couplers and vacuum • Curved Be windows • Ports extruding Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

7. The Cavity Parameters The cavity design parameters • Frequency: 201.25 MHz • β = 0.87 • Shunt impedance (VT2/P): ~ 22 MΩ/m • Quality factor (Q0): ~ 53,000 • Curved Be window radius and thickness: 21-cm and 0.38-mm Nominal parameters for cooling channels in a muon collider or a neutrino factory and MICE • 16+/8 MV/m peak accelerating field • Peak input RF power ~ 4.6/1 MW per cavity (85% of Q0, 3τ filling) • Average power dissipation per cavity ~ 8.4/1 kW • Average power dissipation per Be window ~ 100/12 watts Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

8. The 201 MHz Cavity R&D • Pleasant and effective collaboration between national labs and universities, a short summary of activities: • Cavity design and engineered at LBNL • Curved Be window design and engineering at LBNL and Oxford University • Cavity half-shells spun at ACME, a company in Minnesota • Nose pieces, stiffener rings and fixturing made at University of Mississippi and LBNL • E-beam welding, cavity cleaning and ports extruding at JLab • Design and engineering of RF loop couplers at LBNL • SNS RF windows • Weekly video conference with Jlab, daily updates recently while preparing for the equator welding Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

9. Spinning @ ACME An example of the spinning technique ! Spinning tools Spinning a bowl Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

10. A Spun Half Shell @ ACME August 6, 2003 Inner surface scratch was found after chemical cleaning at JLab, and need to be mechanically buffed and electro-polishing. Can be avoided by carefully monitoring and handling during the spinning. Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

11. RF and CMM Measurements CMM setup and scans at 0, 45 and 90 degrees, respectively Frequency and Q measurements of half shells; Cu tape for better RF contacts Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

12. CMM Profiles 3 CMM scans per half shell conducted at 0o, 45o, 90o, respectively Measured frequency of shell-1: 196.97 MHz (simulated frequency: 197.32 MHz) Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

13. Stiffener Rings Two stiffener rings were fabricated at Mississippi University Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

14. E-Beam Welding Preparation For The Stiffener Rings Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

15. E-Beam Welding of the S. Ring Stiffener ring “Spider” holder Skip e-beam welding first to hold the stiffener ring in place, then finish the complete welding Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

16. After Stiffener Ring Welding Mechanical cleaning of the cavity inner surface (right) after e-beam welding of the stiffener ring (above) Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

17. Machining at JLab Cutting opening for beam iris and nose piece Machining setup Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

18. Recent progress for the welding fmeasured = 200.88 MHz Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

19. Fixturing for the welding Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

20. Ready For Equator Welding Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

21. Extruding tests at JLab Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

22. Prototype of Curved Be windows Collaboration with Oxford University Ms. S. Yang will talk on the window designs and FEA modeling

23. A brief review: Be window R&D • Ideal windows • Transparent to muon beams • Perfect electric boundary to RF field • No detuning to cavity frequency • Engineering solutions • Pre-stressed flat Be windows • Pre-curved Be windows • Grids Window profile evolutions From flat to curved windows A pre-curved Be window: 0.25 mm thick and 21 cm in radius (by Oxford Univ.) Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

24. Curved Be Window Failed in forming Be window at room temperature At that time (last MICE meeting), we believed the curved Be windows can be formed at high temperature (not at LBNL). It can be formed and brazed at Brush-Wellman Company. Purchase order has been placed. We received two curved windows recently. Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

25. Curved Be windows by BWM Two curved Be windows for 805 MHz cavity: 0.254 mm thick and 16-cm diameter Pre-formed the Be foils first at high temperature, brazed copper frames afterwards. The windows will be Ti nitrided at LBNL for high power test at MTA, Fermilab. Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

26. 201 MHz cavity status • Four half shells have been formed by spinning • Cu stiffener rings were e-beam welded to two half shells • The shells are being mechanically cleaned at JLab • Shells are ready for machining prior to e –beam welding of equator joint • Equator weld fixturing has been fabricated at LBNL • Cavity nose piece rings (Univ. of Mississippi) have been brazed at LBNL • Conceptual design of RF loop coupler with SNS RF windows • E-beam welding of equator joint, READY • Extruding four ports, QUALIFIED • Chemical cleaning and electro-polishing of the cavity • Pre-curved Be windows, QUALIFIED • The cavity should be ready for test in MTA at Fermilab this fall Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

27. Summary The 201 MHz cavity design and fabrication go smoothly • Spun shells ready for machining after e-beam welding • Nose pieces, stiffener rings and fixture were made • Support structures for the equator welding Engineering design (details) is still continuing • Ports (succeeded in extruding tests and qualified the techniques) • Couplers (done with conceptual design) • Tuners Significant progress on curved window design and fabrication • Succeeded in making S.S. curved windows • Succeeded in making curved Be windows for 805 MHz cavity by Brush-Wellman company The cavity will be ready for test at MTA, Fermilab this fall ! Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li

28. Questions ? Thank You! Status of 201 MHz Prototype Cavity and Curved Be windows Derun Li