1. 1 Cold L-Band Cavity BPM: Design Status July 2006 Gennady Romanov Linda Valerio Manfred Wendt Fermilab July 21, 2006

2. 2 Backup: Cold BPM Requirements and Issues BPM location in the cryostat, at the SC-quad Every 3 rd 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

3. 3 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

4. 4 Cold Cavity BPM Development Problems with simple “Pill-Box” Cavity BPM’s TM 010 monopole common mode (CM) Cross-talk (xy-axes, polarization) Transient response (single-bunch measurements) Wake-potential (heat- load, BBU) Cryogenic and cleanroom requirements

5. 5 Waveguide-loaded pillbox with slot coupling. Dimensioning for f 010 and f 110 symmetric to f RF, f RF = 1.3 GHz, f 010 ≈ 1.1 GHz, f 110 ≈ 1.5 GHz. Dipole- and monopole ports, no reference cavity for intensity signal normalization and signal phase (sign). Q load ≈ 600 (~ 10 % cross-talk at 300 ns bunch-to-bunch spacing). Minimization of the X-Y cross-talk (isolation). Simple (cleanable) mechanics. Iteration of EM-simulations for optimizing all dimensions. Vacuum/cryo tests of the ceramic slot window. Copper model for bench measurements.

6. 6 General view Ports Discrete port (current) x=10 mm y=30 mm Excitation signal Cavity-BPM: SLAC style

7. 7 Mode Frequency 1 1.017 – Parasitic E 11 -like 2 1.023 – Parasitic E 21 -like 3 1.121 – Monopole E 01 4 1.198 - Waveguide 5 1.465 - Dipole E 11 6 1.627 Dipole Eigen modes Parasitic mode. Coupling through horizontal slots is clearly seen Parasitic mode E z distribution

8. 8 Transient solution. Probe magnitude

9. 9 Cavity-BPM: Pillbox with WG slot coupling

10. 10 EM - Eigen mode solver. FD – frequency domain solver. Slot_L=55 mm and Slot_W = 5 mm -> Q load = 678 Optimization of slot dimensions

11. 11 Frequency, GHz1.46 Loaded Q~ 600 Beam pipe radius, mm39 Cell radius, mm114 Cell gap, mm10 Waveguide, mm122x110x25 Coupling slot, mm47x5x3 Window – Ceramic brick of alumina 96% e r ≈ 9.4 Size: the same as slot Ceramic windows in coupling slots N type receptacle, 50 Ohm, D=9.75 mm d=3.05 mm

12. 12 47.03.mm 2 1 Diam. 4.46 mm 11.13 mm8.9 mm Pick-up dimensions

13. 13 Dipole Mode Sensitivity (Resolution) with:

14. 14 Monopole mode damping using simple pin-antennas

15. 15 Damping with antennas: Transmission-line Combiner. 180 degrees for dipole. Standing wave with some frequency detuning. l TL ~ 200 mm to avoid resonances around 1.46 GHz (SW eigenmodes for l TL ~ 200 mm at: f 3 ~1.1 GHz, f 5 ~1.9 GHz) In phase for monopole

16. 16 Appropriate length of combiner – reasonable length and non-resonant Interaction with dipole mode

17. 17