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Paul Scherrer Institut. Cavity BPM Pickups for SwissFEL Boris Keil for the PSI/GFA Beam Diagnostics Team Paul Scherrer Institut. DEELS Workshop 2014. 12.5.14. Introduction. 1 st construction phase. 2 nd construction phase. Athos 0.7-7nm. SwissFEL Linac-based FEL, photocathode RF gun

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slide1

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

slide2

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

slide3

SwissFEL Site

PSI East

PSI West

SwissFEL

SLS

slide5

SwissFEL Site 6/2013

PSI East

PSI West

Experiment End Stations

Injector

slide6

SwissFEL Site 4/2014

Gun area

Injector & Linac below ground level, technical gallery (incl. klystrons) on top

slide7

SwissFEL Site 4/2014

Experimental area

slide8

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

slide9

BPM Requirements / Specifications

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

slide10

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 …

slide11

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.

slide12

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

slide14

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.

slide15

SwissFEL BPM8 Pickup

8 mm inner beam pipe aperture. Pickup length 100 mm.

Motorized X-Y mover (BPM+quad. magnet

slide16

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]
slide17

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.
slide18

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, ...)

slide19

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.

slide20

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.

slide24

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)
slide25

Mechanical Dimension Def.

Position Cavity

Reference Cavity

slide28

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.
slide31

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)

slide32

BPM16 RFFE Output Signals

SwissFEL BPM prototype: RFFE output signals (IQ outputs, just Q shown)

Low bunch-bunch crosstalk

28ns bunch spacing

slide33

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)

slide34

BPM16 Charge Resolution

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

slide35

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.
slide36

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)
slide37

Paul Scherrer Institut

Thank you for yourattention!

slide40

BPM16 Pre-Series: Frequency

Position Cavity

Reference Cavity