Cavity BPM Pickups for SwissFEL

1. Paul Scherrer Institut Cavity BPM Pickups for SwissFEL Boris Keil for the PSI/GFA Beam Diagnostics TeamPaul Scherrer Institut DEELS Workshop 2014 12.5.14

2. Introduction 1stconstructionphase 2ndconstructionphase Athos 0.7-7nm • SwissFEL • Linac-based FEL, photocathode RF gun • Injector and linac: 2 bunches, 28ns spacing, 100Hz • Fast beam distribution kicker • 2 Undulators, 1 bunch each • Hard X-ray ("Aramis"), 0.1-0.7nm • Soft X-ray ("Athos"), 0.7-7nm user stations 2.6-3.4 GeV BC1 BC2 Injector Linac 1 Linac 2 Linac 3 2.1-5.8 GeV 0.35 GeV 2.0 GeV 3.0 GeV Aramis 0.1-0.7 nm

3. SwissFEL Site PSI East PSI West SwissFEL SLS

4. SwissFEL Site

5. SwissFEL Site 6/2013 PSI East PSI West Experiment End Stations Injector

6. SwissFEL Site 4/2014 Gun area Injector & Linac below ground level, technical gallery (incl. klystrons) on top

7. SwissFEL Site 4/2014 Experimental area

8. E E REF REF E E REF BPM Usage • Alignment of beam trajectory. Orbit feedback. • Measurement of beam Energy: • - In bunch compressors: • Standard BPMs in bunch compressor “arms” • (no special large-aperture BPM needed), plus two • non-dispersive REFerence BPMs for x/y jitter removal. • - In dog-legs / beam dumps • Standard BPMs used to measure energy in log-leg / • beam dump “arms”. No special ultra-large-aperture • beam dump BPM needed. • Relative beam charge measurement (absolute • calibration via dedicated Bergoz charge monitor). • Correction of position-/charge-dependent measurement • errors of other systems (BAM, wire scanner, ...). beam

9. BPM Requirements / Specifications * Desired: Support of larger/smaller range (via remote gain control), but with lower/higher resolution.

10. BPM Type Choice Evaluation of BPM Types For SwissFEL Fulfill requirement for injector, linac, TL Fullfill requirements for all BPMs “Typical” noise: Examples & estimates (scaling, …) based on existing systems, not theoretical limit …

11. Pickup Parameters * Undulators (Alternative Option): Single-channel downconversion feasible, being evaluated. ** Sample rates of available ADCs for European XFEL (E-XFEL) BPM electronics built by PSI *** E-XFEL Undulator: 2.9 V/mm/nC (Q=70) -> ~3x improved low charge resolution for SwissFEL.

12. SwissFEL BPM16 Pickup • Based on E-XFEL/SACLA design • Optimized for low charge & low • production costs. Position resonator (used signal ~ position*charge). Resonator gap width “Waveguide depth” Reference resonator (used signal ~ charge) Waveguides connected to beam pipe

13. SwissFEL BPM16 Pickup 16 mm 100 mm

14. SwissFEL BPM38 Pickup Reference resonator (2 RF feed-throughs): Signal ~ charge 38 mm 255 mm TM010-suppressing waveguide Dipole resonator (4 RF feed-throughs) Signal ~charge*pos.

15. SwissFEL BPM8 Pickup 8 mm inner beam pipe aperture. Pickup length 100 mm. Motorized X-Y mover (BPM+quad. magnet

16. BPM16 Pickup Production Steps • Production Steps (Complete Pickup): • Machining of three pickup body parts from metal block [Company] • Mechanical measurement [Company] • RF test (Q, frequency) [PSI] • Brazing of three body parts (foil) [PSI] • Leak test, RF test (Q, frequency) [PSI] • Welding of RF feed-throughs to body [PSI] • Final vacuum & RF test. [PSI] • Production Steps (Feedthroughs): • Machining of pickup metal parts [Company] • Production of boro-silicate "pill" (sintered granulate) [Company] • Loose assembly, then oven to melt glass [Company] • Tests: Vacuum, dimensions [Company] • Test: RF (reflection) [PSI]

17. BPM16 Pickup Costs • Body Parts (316LN Stainless Steel) • Design already well optimized by SACLA/DESY • SwissFEL: Only low-charge performance optimized • Costs of different companies differ a lot (1400CHF • to 3800EUR per pickup, material + machining + meas. ...). • Feedthroughs (FTs) • Few years ago: SACLA designed FT for their cavity • BPMs. Single supplier, PSI paid ~500EUR per FT in 2010 • = ~half of overall pickup costs! • Several companies offered compatible type for E-XFEL, • typ. few 10% cheaper • PSI developed FT in collaboration with Swiss company • specialized in high-volume low-cost glass FTs (airbags: • few million glass ceramic FTs per year!, medical, ...). • Price reduced ~5x compared to initial design.

18. SwissFEL Cavity BPM Feedthrough Feedthrough production (@BC-Tech AG): Some iterations were necessary until our requirements were met (size of glass pearl, modification of graphite stamp, ...)

19. Neutron Scattering Images of FTs Also feedthtoughs from other companies evaluated ... Vacuum side Borosilicate glass seal (good neutron absorber, not well visible with X-rays ...) Idea: M. Rohrer (had neutron scattering image of gun bullet on his desk ...). Did not show difference between good & bad VSWR. But: ... air side Bad vacuum design: Risk of inner leaks.

20. Feedthrough RF Testing Tool 50 Ω broadband load Feedthrough to be tested APC7-N adapter Series production: Tool for fast RF test of all feedthroughs.

21. S11 for Feedthrough Pre-Series

22. S11 for Feedthrough Pre-Series

23. S11 for Feedthrough Pre-Series

24. BPM16 Pickup & Support • Most pickups: Cheap rigid support, • adjustment via shimming (~10um • X/Y steps/reproducibility) • Fewpickups: Support adjustable • via screwswith differential threads • (~1um X/Y steps/reproducibility)

25. Mechanical Dimension Def. Position Cavity Reference Cavity

26. BPM16 Mechanical & RF Tolerances

27. BPM16 Mechanical & RF Tolerances

28. Pre-Brazing Pickup RF Test • Tool fixes body • partsand RF • feedthroughs in • correctposition • pressure/weight • usedtoget • contact. • Measure Q and • frequencyof • all pickups • beforeand after • brazing/welding.

29. RF Meas. Before Brazing

30. RF Meas. After Brazing

31. BPM16 Pickup: Beam Signals Decay to 0.07% Decay to 1.6% Raw signals of SwissFEL BPM16 (QL=40) & E-XFEL undulator cavity pickup (QL=70)

32. BPM16 RFFE Output Signals SwissFEL BPM prototype: RFFE output signals (IQ outputs, just Q shown) Low bunch-bunch crosstalk 28ns bunch spacing

33. BPM16 Position Resolution SwissFEL BPM16 position resolution measurement: Difference of SwissFEL & E-XFEL (extrapolated) BPM position reading. <0.8μm RMS noise at 135pC & 0.35 mm offset (range > ±1mm)

34. BPM16 Charge Resolution SwissFEL BPM16 Charge resolution measurement: Correlation with E-XFEL undulator BPM. <0.1pC RMS charge noise at 135pC bunch charge.

35. Summary & Conclusions • SwissFEL usesonlycavity BPM pickups. • In-house feedthrough design & collaborationwith • Swiss large-scale (automotive/medical) non-RF feed- • throughmanufacturerallowedsignificantpricereduction. • BPM16 prototypesmeetrequirements. Currentlydoing • minorredesign, removingsystematic Q andfrequency • shiftof final version (with BC-Tech feedthroughs) • BPM38 and BPM8 prototype beam tests 7-9/2014 • Neutron scatteringallowed non-desctructiveanalysis • of feedthroughs from alternative manufacturer.

36. Team & Acknowledgements • F. Marcellini, M. Rohrer (Cavity pickup & feedthrough design & test) • M. Stadler (Cavity RFFE, algorithms, overall system tests) • M. Roggli, R. Ditter, R. Kramert (ADC Mezzanine, BPM crate) • R. Baldinger (FPGA carrier board) • G. Marinkovic, W. Koprek (Software & FPGA firmware) • and • PSI Mechanical Department (Pickup construction & prototyping) • Colleagues from DESY and SACLA (Pickup infos & tips) • C. Bargähr (RF feedthroughs, www.bctech.ch)

37. Paul Scherrer Institut Thank you for yourattention!

38. Supplementary Slides …

39. BPM16 Pre-Series: Dimensions

40. BPM16 Pre-Series: Frequency Position Cavity Reference Cavity