Cold Cavity BPM R&D for the ILC

1. Cold Cavity BPM R&Dfor the ILC Manfred Wendt Fermilab Global Design Effort

2. The International Linear Collider ILC Beam Parameters (nominal): Global Design Effort

3. ILC Beam Instrumentation • ~ 2000 Button/stripline BPM’s • ~ 1800 Cavity BPM’s (warm) • 770 Cavity BPM’s (cold, part of the cryostat) • 21 LASER Wirescanners • 20 Wirescanners (traditional) • 15 Deflecting Mode Cavities (bunchlenght) • ~ 1600 BLM’s • Many other beam monitors, including toroids, beam phase monitors, wall current monitors, faraday cups, OTR & other screen monitors, sync light monitors, streak cameras, feedback systems, etc. Global Design Effort

4. Cold BPM Requirements • BPM location in the cryostat, at the SC-quad • Every 3rd cryostat is equipped with a BPM/quad: 650x cold BPM’s total. • Real estate: ~ 170 mm length, 78 mm beam pipe diameter (???). • Cryogenic environment (~ 4 K) • Cleanroom class 100 certification (SC-cavities nearby!) • UHV certification • < 1 µm single bunch resolution, i.e. measurement (integration) time < 300 ns. • < 200 µm error between electrical BPM center and magnetic center of the quad. • Related issues: • RF signal feedthroughs. • Cabling in the cryostat • Read-out System Global Design Effort

5. Possible Cold BPM Solutions • Dedicated, high resolution BPM (baseline design): Cavity BPM, based on the characterization of beam excited dipole eigenmodes, also requires the measurement of the monopole modes for normalization and evt. sign of the beam displacement. • Combination of dedicated, lower resolution BPM’s and HOM coupler signal BPM’s (alternative design): • Simple, button style BPM’s (~ 50 µm resolution) for machine tune-up and single bunch orbit measurements. • HOM coupler BPM signal processor as high resolution BPM Global Design Effort

6. Cavity BPM Principle Problems with simple “Pill-Box” Cavity BPM’s • TM010 monopole common mode (CM) • Cross-talk (xy-axes, polarization) • Transient response (single-bunch measurements) • Wake-potential (heat-load, BBU) • Cryogenic and cleanroom requirements Global Design Effort

7. CM-free Cavity BPM • uses waveguide ports to suppress the monopole mode (no hybrid-junction required) • very high resolution potential (~ 20 nm)! • complicated mechanics, i.e. cleanroom and cryogenic issues Global Design Effort

8. KEK ATF nanoBPM Collaboration BINP cavity BPM: • C-Band (6426 MHz) • 20 mm aperture • Selective dipole-mode waveguide couplers • 3 BPM’s in a LLBL hexapod spaceframe (6 degrees of freedom for alignment) • Dual-downconversion electronics (476 & 25 MHz) • 14-bit, 100 MSPS digitizer Global Design Effort

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10. Cavity BPM Resolution at ATF • 10 minute run • 800 samples • σ ≈ 24 nm Move BPM in 1 µm steps Global Design Effort

11. SLAC Cavity BPM • S-Band design for 35 mm beam-pipe aperture • Waveguide cut to beam-pipe (better cleaning) • Successful beam measurements at SLAC-ESA (~ 0.8 µm resolution) • No cryogenic temperature tests so far. • No clean-room certification • Needs a reference cavity or signal • Reduced beam-pipe aperture (nominal: 78 mm) Global Design Effort

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16. Cold L-Band Cavity BPM Design • Waveguide-loaded pillbox with slot coupling. • Dimensioning for f010 and f110 symmetric to fRF, fRF = 1.3 GHz, f010 ≈ 1.1 GHz, f110 ≈ 1.5 GHz. • Dipole- and monopole ports, no reference cavity for intensity signal normalization and signal phase (sign). • Qload ≈ 600 (~ 10 % cross-talk at 300 ns bunch-to-bunch spacing). • Minimization of the X-Y cross-talk (dimple tuning). • Simple (cleanable) mechanics. • Iteration of EM-simulations for optimizing all dimensions. • Vacuum/cryo tests of the ceramic slot window. • Copper model for bench measurements. Global Design Effort

17. Scaling of the SLAC Cavity BPM Discrete port (current) x=10 mm y=30 mm Excitation signal Ports General view Global Design Effort

18. SLAC BPM (scaled): Eigen Modes • Mode Frequency • 1.017 – Parasitic E11-like • 1.023 – Parasitic E21-like • 1.121 – Monopole E01 • 1.198 - Waveguide • 1.465 - Dipole E11 • 1.627 Dipole Parasitic mode. Coupling through horizontal slots is clearly seen Parasitic mode Ez distribution Global Design Effort

19. Pillbox with WG Slot Coupling Global Design Effort

20. Optimization of the Slot Dimensions • EM: Eigen-mode solver • FD: Frequency-domain solver • Slot-L = 55 mm & Slot-W = 5 mm Qload = 678 Global Design Effort

21. Ceramic Windows in the Coupling Slots Window – Ceramic brick of alumina 96% er≈ 9.4 Size: the same as slot N type receptacle, 50 Ohm, D=9.75 mm d=3.05 mm Global Design Effort

22. Matched WG-to-Coaxial Transition 11.13 mm 8.9 mm 47.03.mm 1 2 Diam. 4.46 mm Global Design Effort

23. Dipole Mode Sensitivity (Resolution) with: with: Global Design Effort

24. Monopole-Mode Investigation Monopole mode damping using simple pin-antennas Global Design Effort

25. Unmatched Transmission-line Combiner • 180 degrees for dipole-mode. Standing wave with some frequency detuning. • lTL~ 200 mm to avoid resonances around 1.46 GHz (SW eigenmodes for lTL~ 200 mm at: f3 ~1.1 GHz, f5 ~1.9 GHz) In-phase signal combining for the monopole-mode signal Global Design Effort

26. Combiner-induced Frequency-shift Appropriate length of combiner – reasonable length and non-resonant Interaction with dipole mode Global Design Effort

27. Test Model for N2 Temperature Cycles Global Design Effort

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32. L-Band Cavity Assembly Global Design Effort

33. Next Steps… • N2 temperature cycles with the test model. • Drafting of the complete assembly. • EM modeling and fine tuning of the dimensions. • Investigation of the tolerances. • Prototype manufacturing. • RF measurements and characterization. Thanks for your patience! Global Design Effort