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
Cavity BPM Pickups for SwissFEL
Boris Keil for the PSI/GFA Beam Diagnostics TeamPaul Scherrer Institut
DEELS Workshop 2014
Aramis 0.1-0.7 nm
Experiment End Stations
Injector & Linac below ground level, technical gallery (incl. klystrons) on top
* Desired: Support of larger/smaller range (via remote gain control), but with lower/higher resolution.
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 …
* 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.
Position resonator (used signal ~ position*charge).
Resonator gap width
Reference resonator (used signal ~ charge)
Waveguides connected to beam pipe
Reference resonator (2 RF feed-throughs): Signal ~ charge
Dipole resonator (4 RF feed-throughs) Signal ~charge*pos.
8 mm inner beam pipe aperture. Pickup length 100 mm.
Motorized X-Y mover (BPM+quad. magnet
Feedthrough production (@BC-Tech AG): Some iterations were necessary until our
requirements were met (size of glass pearl, modification of graphite stamp, ...)
Also feedthtoughs from other companies evaluated ...
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: ...
Bad vacuum design: Risk of inner leaks.
50 Ω broadband load
to be tested
Series production: Tool for fast RF test of all feedthroughs.
Decay to 0.07%
Decay to 1.6%
Raw signals of SwissFEL BPM16 (QL=40) & E-XFEL undulator cavity pickup (QL=70)
SwissFEL BPM prototype: RFFE output signals (IQ outputs, just Q shown)
Low bunch-bunch crosstalk
28ns bunch spacing
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)
SwissFEL BPM16 Charge resolution measurement: Correlation with E-XFEL undulator BPM. <0.1pC RMS charge noise at 135pC bunch charge.
Thank you for yourattention!