Overview of the RFCC Module and 201-MHz Cavity Design

1. Overview of the RFCC Module and 201-MHz Cavity Design Derun Li Lawrence Berkeley National Laboratory RFCC Module Preliminary Design Review June 4, 2008

2. Outline • Introduction of RFCC module of MICE cooling channel and charge of the review • Review of the 201-MHz cavity design • MuCool 201-MHz prototype cavity: baseline design for MICE • Prototype: collaboration between LBNL, JLab, University of Mississippi and Oxford University • Physics design and cavity fabrications • Cavity body • RF coupler • Be windows • Tuners • Recent progress • Vendor identification • Engineering CAD model • Integration and interface • Summary Derun Li - Lawrence Berkeley National Lab - June 4, 2008

3. International Muon Ionization Cooling Exp. RFCC RFCC Spectrometer Solenoid 1 AFC AFC Spectrometer Solenoid 2 Absorber and Focusing Coil (AFC) Derun Li - Lawrence Berkeley National Lab - June 4, 2008

4. Eight 201-MHz Cavities for MICE Eight201-MHz RF cavities MICE Cooling Channel Courtesy of S. Q. Yang, Oxford Univ. RFCC modules Derun Li - Lawrence Berkeley National Lab - June 4, 2008

5. SC coupling Coil Curved Be window Cavity Couplers Vacuum Pump 201-MHz cavity RFCC Module Derun Li - Lawrence Berkeley National Lab - June 4, 2008

6. Charge of this Review • Evaluate the preliminary engineering design of RFCC module • Evaluate engineering design of MICE 201-MHz RF cavity • Is LBNL ready to purchase long lead cavity materials and components? • Copper sheets for cavity bodies • Thin, curved beryllium windows • Ceramic RF windows • Evaluate engineering design and fabrication scheme of the 201-MHz cavity to determine readiness to initiate cavity body fabrication • Spinning of cavity shells • e-beam welding • Port extruding • Tuners • Cavity support • Evaluate overall module concept • Interface with other modules • Site interfaces • Integration and shipping • Detailed design of CC is not part of this review Derun Li - Lawrence Berkeley National Lab - June 4, 2008

7. RFCC Design Review Agenda 14:00 Overview: prototype cavity, physics design and recent progress by Derun Li 14:40 201 MHz Mechanical Design and Analysis by Allan DeMello 15:20 Other Cavity Components by Allan DeMello 15:40 Coffee Break  15:55 Overall RFCC Module Mechanical Design by Allan DeMello 16:25 Shipping, Installation and Interfaces by Steve Virostek 16:45 RFCC Schedule and Manpower by Steve Virostek 17:00 Discussion All 17:15 Committee closed session 17:45 Closeout All Derun Li - Lawrence Berkeley National Lab - June 4, 2008

8. MuCool 201-MHz RF Prototype Cavity • MICE 201-MHz cavity design is based on MuCool prototype cavity with minor differences • Prototype cavity • Physics Design • Couplers and ceramic RF windows • Engineering • Fabrication: cavity body, ports, tuners, etc. • Large, pre-curved and thin 42-cm diameter Be windows • Commissioning and operation • RF Conditioning and background • High gradients (~ 16 MV/m) • With the thin and curved Be windows • With external magnetic fields Derun Li - Lawrence Berkeley National Lab - June 4, 2008

9. The Cavity Body Profile Spherical section at the equator to ease addition of ports (±~ 6.5o) Elliptical-like (two circles) nose to reduce peak surface field Stiffener ring 2o tilt angle 42-cm 6-mm Cu sheet allows for uses of spinning technique and mechanical tuners similar to SCRF ones 121.7-cm De-mountable Pre-curved Be windows to terminate RF fields at the iris Low peak surface E-field at iris Derun Li - Lawrence Berkeley National Lab - June 4, 2008

10. Cavity Design Parameters • The cavity design parameters • Frequency: 201.25 MHz • β = 0.87 • Shunt impedance (VT2/P): ~ 22 MΩ/m • Quality factor (Q0): ~ 53,500 • Be window diameter and thickness: 42-cm and 0.38-mm • Nominal parameters for MICE and cooling channels in a neutrino factory • 8 MV/m (~16 MV/m) peak accelerating field • Peak input RF power: 1 MW (~4.6 MW) per cavity • Average power dissipation per cavity: 1 kW (~8.4 kW) • Average power dissipation per Be window: 12 watts (~100 watts) Derun Li - Lawrence Berkeley National Lab - June 4, 2008

11. 201 MHz Cavity Concept Spinning of half shells using thin copper sheets and e-beam welding to join the shells; extruding of four ports; each cavity has two pre-curved Beryllium windows, but also accommodates different windows Derun Li - Lawrence Berkeley National Lab - June 4, 2008

12. Shell Measurement at LBNL Measured frequency of shell-1: 196.97 MHz; Simulated frequency: 197.32 MHz,  f ~ 350 kHz • CMM scans to measure the • spun profiles of shells • Frequency and Q measurements • Copper tapes for better RF • contacts Profile measurements: 3 CMM scans per half shell conducted at 0o, 45o, 90o, respectively Derun Li - Lawrence Berkeley National Lab - June 4, 2008

13. Fabrication of the MuCool Cavity • Two 6-mm thick copper shells are formed from annealed, flat sheet using a spinning technique • Two half shells are e-beam welded together at equator to form the cavity • Separate copper nose piece rings are e-beam welded to cavity iris (aperture) • RF and vacuum ports are formed by pulling a die through a hole cut across the equator weld (extruding) • Externally brazed tubes provide cooling • Cavity inside surfaces are finished by mechanically buffing and electro-polishing • Two thin, pre-curved beryllium windows are mounted on cavity aperture • Cavity is mounted between two thick aluminum vacuum support plates • See Allan DeMello’s talks for details for fabrication and QC Derun Li - Lawrence Berkeley National Lab - June 4, 2008

14. Prototype RF Coupler • Two loop couplers each cavity to give critical coupling • Prototype coupling loop design uses standard off-the-shelf copper co-axial components • Parts were joined by torch brazing at LBNL • Coupling loop has integrated water cooling lines • Two SNS style RF windows mfg. by Toshiba • High power tested up to 2.5 MW per coupler, 10 kW (avg.) Ceramic RF window RF Window Conditioning Loop coupler made at LBNL SNS RF window Derun Li - Lawrence Berkeley National Lab - June 4, 2008

15. Thin and Curved Be Windows • Each cavity has two Be windows • 42-cm diameter and 0.38-mm thick • Window is formed at high temperature and later brazed to copper frames • Thin TiN coatings on both sides of the window • One window curves into the cavity and one curves out • Already high power tested up to 5 MW in 201-MHz cavity at MTA, FNAL 42-cm Derun Li - Lawrence Berkeley National Lab - June 4, 2008

16. Low Power RF Measurements at MTA • f =199.578 MHz • Q0 =49,000 ~ 51,000(with flat copper windows; better than • 90% of the design value) • Two couplers • Balanced • Coupling adjustments Derun Li - Lawrence Berkeley National Lab - June 4, 2008

17. Dial indicators Tuner Concept and Measurements • Mechanical tuning plates at four locations • Dial indicators to measure displacement between Al plates • Tuning measurement in air • Equivalent to MICE cavity under vacuum • Adjusted up to 2-mm with 8 steps of 0.25-mm each • Measured tuner sensitivity • 156 kHz/mm per side • Calculated tuner sensitivity • 230 kHz/mm per side • Discrepancy is due to deflection of the Al plates Derun Li - Lawrence Berkeley National Lab - June 4, 2008

18. RF Test Setup at MTA The 805-MHz and 201-MHz cavities at MTA, FNAL for RF breakdown studies with external magnetic fields. 201 MHz cavity 805 MHz pillbox cavity Derun Li - Lawrence Berkeley National Lab - June 4, 2008

19. High Power RF Tests with Cu & Be Windows • The cavity was first tested with flat copper windows and reached ~ 16 MV/m quickly and quietly • The cavity then was tested with thin and curved Be windows and again reached to ~19 MV/m quickly • Cavity frequency had to be retuned • Cavity frequency was stable during the operation, however, we did observe frequency shift due to RF heating on the windows • Frequency shift of ~ 125 kHz (from 0 to ~ 19 MV/m, 150-micro-second pulse, 10-Hz repetition rate) in ~ 10 minutes, well within the tuning range (230 kHz/mm per side,  2-mm range) • With a few hundred Gauss stray field from Lab-G magnet, the cavity gradient can be maintained at 19 MV/m • To test with stronger external magnetic fields • Move the cavity closer to Lab-G magnet • SC coupling coil for MuCool Derun Li - Lawrence Berkeley National Lab - June 4, 2008

20. Lab-G magnet The 201-MHz cavity Tests with Stronger Magnetic Fields • New vacuum pumping system • Separation of the nearest curved Be window from the face of Lab-G magnet is 10-cm (before was 110-cm) • Maximum magnetic field near the Be window 1.5 Tesla (at 5 Tesla in magnet) • Test Results: • Multipactoring was observed over the entire magnetic field range up to 1.1-T at nearest Be window • A strong correlation exists between cavity vacuum and radiation levels • We have achieved ~ 14 MV/m at 0.75-T to the nearest curved thin Be window • The test results are very encouraging, data analysis is being conducted Derun Li - Lawrence Berkeley National Lab - June 4, 2008

21. Recent Progress • RFCC engineering CAD model • RF and Engineering design of 201-MHz RF cavity • Integration and interface • Vendor identifications Derun Li - Lawrence Berkeley National Lab - June 4, 2008

22. Recent Progress: RF Cavity Design • See A. DeMello’s talks on details • Vendor Identification • Engineering CAD model • Integration and interface • Improved Be window design • Tuners and support • Cavity post processing • Cavity RF design • 3-D CST MWS RF parameterized model with ports and curved Be windows • Hard to reach the design frequency by spinning • Frequencies between cavities should be able to achieve within  100 kHz • Approaches • Modification the spinning form • Targeting for higher frequency • Fixed tuner to tune cavity close to design frequency (deformation of cavity body) • Tuners are in push-in mode  lower frequency Derun Li - Lawrence Berkeley National Lab - June 4, 2008

23. Numerical Study with B Field • Preliminary studies, in collaboration with colleagues at SLAC using Omega-3P and Track-3P codes • Cavity with flat windows: 5 MV/m on axis; 2-T uniform external magnetic field; scan of a few points from one cavity side Trajectories with external B = 2-T field Trajectories without external B field E field contour Derun Li - Lawrence Berkeley National Lab - June 4, 2008

24. Summary • MICE cavity design is heavily based on successful MuCool 201-MHz prototype RF cavity and lessons learned • Fabrication and post processing • Cavity conditioning and operation • Engineering design of the cavity is essentially complete • CAD model of the cavity, tuners, support and vacuum • Fabrication schemes • Significant progress on engineering designs of RFCC module • Possible operation at LN temperature? • Current design accommodates LN operation, but it looks very challenging Derun Li - Lawrence Berkeley National Lab - June 4, 2008