A Transverse Profile Imager for SwissFEL Rasmus Ischebeck

Transcription

1 PAUL SCHERRER INSTITUT observer s virtual image d scnitillating crystal primary beam A Transverse Profile Imager for SwissFEL

2 A Transverse Profile Imager for SwissFEL > Profile measurement in FELs observer s scnitillating crystal virtual image d > Imaging scintillating crystals x 10 5 primary beam normalized x x 10 5 normalized yp x > 0 Applications normalized y 2 x

3 Transverse Profile Monitors University of Illinois 3

4 Profile Measurement in FELs 3.5 x y / mm x / mm 4

5 Coherent Optical Transition Radiation Coherent OTR Up to X100,000 enhancement observed OTR11, OTR21 inserted, no coherence No upstream screens, X10,000 less attenuation 11 Joe Frisch 5

6 Coherent OTR COTR at Other Labs COTR spikes at APS Injector, at 2X minimum bunch length (Lumpkin et. al. Zeuthen m April 08.) COTR at DESY/FLASH At max compression 12 Joe Frisch 6

7 1-Dimensional Profile Monitor Lost charge / percent Wire position / mm Gian Luca Orlandi, Prajwal Mohanmurthy 7

8 x-y Correlations > Intrinsic correlation y / mm x / mm > Explicit x-y dependency introduced by RF deflector 8

9 A Transverse Profile Imager for SwissFEL > Profile measurement in FELs observer s scnitillating crystal virtual image d > Imaging scintillating crystals x 10 5 primary beam normalized x x 10 5 normalized yp x > 0 Applications normalized y 2 x

10 2-Dimensional Profile Monitors > Optical transition radiation (OTR) > Scintillation 10

11 Imaging Scintillators a) b) c) d) e)

12 Electron Beam Profile Monitors Scintillators, OTR Screens & Wire Scanners Alignment hole and calibration scale Wire scanner Fluorescent crystal (Ce:LuAG) Installed scintillators Ce:YAG 5 µm 20 µm 200 µm Ce:LuAG 200 µm OTR screen (Al-coated Si wafer) RF shield High Energy Screen Low Energy Screen Scintillators for SwissFEL 12

13 Electron Beam Profile Monitors Visual Light Optics OTR screen / scintillator is at an angle of 45º to the optical axis For overview camera (1:5.3 demagnification) Use Scheimpflug criterion to correct image plane orientation For 1:1 imaging Projected pixel size: 23 µm Perspective control lens is not available commercially Only central part (~1 2 mm) of the screen can be imaged within depth of field Scintillators for SwissFEL 13

14 Design Considerations > Scheimpflug imaging principle Observation of the Scheimpflug imaging principle allows to image the entire screen without depth- of-field issues. To avoid astigmatism, the lens is not tilted, but the detector is tilted. For a 1:1 imaging, we tilt the CMOS sensor by 15º. > Snell s law of refraction observer s ideal observation angle The YAG / LuAG scintillators are observed at such an angle that Snell s law of refraction is observed. As a consequence, we can image beams that are smaller than the thickness of the scintillator. scnitillating scintillating crystal virtual image virtual image aligned with beam axis d primary beam 14

15 Imaging Scintillating Crystals observer s scnitillating crystal virtual image d primary beam 15

16 Imaging Scintillating Crystals s C B scnitillating crystal l d A primary beam 16

17 Imaging Scintillating Crystals observer s scnitillating crystal virtual image d primary beam 17

18 Imaging Scintillating Crystals ideal observation angle scintillating crystal virtual image aligned with beam axis d primary beam 18

19 Trigonometry 19

20 Observed Beam Size apparent transverse size s / µm observation angle β / degrees 20

21 Ideal Observation Angle a) b) 21

22 Measurement Principle > Combination of two monitors: > Scintillating crystal > Optical transition radiation OTR Scintillator OTR 22

23 Implementation (coherent) OTR to camera 23

24 Screen Monitor 24

25 A Transverse Profile Imager for SwissFEL > Profile measurement in FELs observer s scnitillating crystal virtual image d > Imaging scintillating crystals x 10 5 primary beam normalized x x 10 5 normalized yp x > 0 Applications normalized y 2 x

26 Quadrupole Scan normalized xp x normalized x x 10 5 normalized yp x normalized y x sigma x [mm] sigma y [mm] measurement index measurement index Pull x 2 Pull y measurement index measurement index 26

27 Beam Transmitted Through Slit y / mm σ x = 20.8µm x / mm 27

28 Slice Emittance Measurements > Slice emittance measurement of a 1.3 pc beam Measurement performed by Eduard Prat & Marta Divall 200 µm 28

29 Slice Emittance Measurement Emittance [nm] CORE SLICE EMITTANCES / OPTICS ex = 34 ± 1 nm bx = 8.52 ± 0.22 m ax = 0.05 ± 0.03 Mx = 1.42 PROJECTED EMITTANCES / OPTICS ex = 40 ± 1 nm bx = ± 0.21 m ax = 0.14 ± 0.02 Mx = t [ps] Mismatch parameter t [ps] Eduard Prat 29

30 Slice Emittance Measurements > Core slice emittance as a function of charge 300 Measurements performed by Eduard Prat & Marta Divall 250 Core slice emittance / nm Charge / pc 30

31 A Transverse Profile Imager for SwissFEL > A transverse profile imager that considers > Snell s law of refraction in the scintillating crystal > The Scheimpflug imaging condition > Prototype installed at the SwissFEL Injector Test Facility > Resolution measured with this prototype: σ 10 µm, ε 30 nm > Sensitivity: Q 1 pc Next Plans > Prove immunity to coherent OTR > Start series production 31

32 Thank You to > Hansueli for the technical design > The AMI team for manufacturing the components > Markus for the assembly > Markus, Albert & the vacuum group for installation > Eduard the emittance measurement software, and for using the new profile monitor extensively for emittance measurements > Gian Luca, Marta, Simona, Carlo, Thomas & Eduard for the measurements presented in this talk > Vincent for help with optical design > Andrea for support with patenting the design, and with connections to industry > Helge for camera server software, and Babak for synchronized data acquisition > The entire Commissioning and Operations crew 32

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