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805-MHz Cavity Refurbishment and suggestions on future tests Derun Li and Robert Rimmer*

805-MHz Cavity Refurbishment and suggestions on future tests Derun Li and Robert Rimmer* Lawrence Berkeley National Laboratory *Jefferson Laboratory RF Workshop at Fermilab October 15, 2008. Coupler. Thin Cu window and end- plate. RF Power. Thermo-couples or view ports.

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805-MHz Cavity Refurbishment and suggestions on future tests Derun Li and Robert Rimmer*

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  1. 805-MHz Cavity Refurbishment and suggestions on future tests Derun Li and Robert Rimmer* Lawrence Berkeley National Laboratory *Jefferson Laboratory RF Workshop at Fermilab October 15, 2008 D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  2. Coupler Thin Cu window and end- plate RF Power Thermo-couples or view ports Waveguide + window Be (or Cu) windows film Up to three RF probes Three more view ports on the equator Pillbox cavity Superconducting magnet The 805-MHz Cavity The cavity has been tested for over six years. D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  3. Cavity modified to house buttons The 805-MHz Cavity with RF Button D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  4. Surface Damage: windows, RF button Windows Button holder Cu button D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  5. Inspection of the Damaged Cavity Surface The cavity is at JLab now. Damage found at the Kidney- shape RF coupler and cavity surface that faces the coupler D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  6. Cavity Repair Setup D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  7. Cleaning of the Damaged Cavity Surface The cavity body surface has been cleaned The outer edge of the kidney-shape coupler has been rounded by 2-mm Inside edge is being polished by hands D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  8. Cavity Repair Status • The cavity surface has been cleaned very well • Should be as good as it was, • Will condition well without magnetic fields • With magnetic fields? • Do we want to do EP? • Help prevent from field emission • Can be done at JLab, time to set up + chemicals • Possible problem? • Trapped chemicals due to the cavity history • Cleaning • Damaged button holder • Exam with microscope to measure pit sizes per R. Palmer’s request • Should we make a new button holder? D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  9. Tests with Buttons • More tests using the repaired cavity with buttons • Previous test results or gradient limits might be limited by damaged surface, not peak fields on buttons • How about a double button configuration? • Two buttons for each material or coating • SUPERFISH simulations show f = 805.89-MHz • Inspect surface damage for each button experiment button D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  10. Do We Need A New Cavity? • IF the repaired cavity does not work well as we expected, we should consider to build a new cavity at 805-MHz cavity. If the answer is yes, • What’s kind of cavity? • Would be nice to have a cavity that can be rotated inside Lab-G magnet to study ExB effects: • Coupler design • In fact, we may learn from any angle configurations, with help from powerful simulation tools D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  11. The 201-MHz Cavity The MUCOOL prototype cavity (3-D model) f = 199.927 MHz Electric field distribution on axis (two curved windows) D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  12. New Ideas for 201-MHz RF Programs? D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  13. Test B-Field Effects • Needs the SC coupling coil • Field map is not the same as in the cooling channel • How about a coaxial quarter wave cavity? • Test 0, 90, and other angles Mechanical stability Water cooling Coaxial quarter- wave cavity A folded quarter-wave cavity: more stored energy D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  14. Coaxial Coupler in B • Coaxial loop couplers for MICE 201-MHz cavities are close to SC coupling coil magnet • Potential RF breakdown in external magnetic fields • May need Ti-N coating? • What tests can be done? • Any suggestions? D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  15. Multipacting Simulation for Muon Collider Cavity Lixin Ge and Zenghai Li Advanced Computations Department Stanford Linear Accelerator Center August 21, 2008 D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  16. Numerical Study with B Field • Preliminary studies, in collaboration 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 D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  17. Multipacting w/ & w/o External Axial Magnetic Field Impact energy of resonant particles vs. field level w/o external B field w/ 2T external axial B field High impact energy (heating?) SEY > 1 for copper SEY > 1 for copper Impact energy too low for MP • 2 types of resonant trajectories: • Between 2 walls – particles with high impact energies and thus no MP • Around iris – MP activities observed below 1 MV/m 2T Resonant trajectory D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  18. Multipacting w/ External Transverse Magnetic Field Impact energy of resonant particles vs. field level w/ 2T transverse B field w/ 2T B field at 10 degree SEY > 1 for copper SEY > 1 for copper • 2 types of resonant trajectories: • Between upper and lower irises • Between upper and lower cavity walls • Slight MP activities observed above 6 MV/m • 2 types of resonant trajectories: • One-point impacts at upper wall • Two-point impacts at beampipe • MP activities observed above 1.6 MV/m 2T 2T D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  19. Simulation Condition • Geometry: Pure pill box • Radius: 0.1425m • Length: 0.1m • Field: • 0 mode • Frequency: 805MHz • Multipacting Simulation Condition: • Average Field Level Scan: 0-60MV/m, interval: 0.5MV/m • External Magnetic Field: 2T • Scan Angle: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 deg • Time step: 0.001 period to resolve external magnetic field • Total Particles: 164x1000x11x61x2=220,088,000 • Each field level running 30 periods D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  20. Impact energy of resonant particles vs. field level Multipacting without External Magnetic Field Resonant trajectory at 5MV/m High impact energy (heating?) E magnitude field B magnitude field D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  21. With External Transverse Magnetic Field No resonant trajectory when angle < 7 deg 2T Single Impact Energy vs. field level for 4 deg D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

  22. Multipacting with External Transverse Magnetic Field Impact energy of resonant particles vs. field level Resonant Trajectory at 50 MV/m with 2T external magnetic field(10 deg angle) 2T D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008

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