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Transcript of Wir schaffen Wissen – heute für morgen Vienna, 08.05.2014 Paul Scherrer Institut Profile...
Wir schaffen Wissen – heute für morgen
Vienna, 08.05.2014Vienna, 08.05.2014
Paul Scherrer Institut
Profile Measurements at Light Sources and FELs
Volker Schlott
Overview
• Synchrotron Radiation Monitors for Light Sources
• Synchrotron Radiation Monitors for FELs
• Screen Monitors for FELs
• Wire Scanners for FELs
• Summary and Outlook
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Acknowledgements
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
…most of the material presented in this overview relies on the outstanding work of many colleaguesfrom various accelerator facilities and has been taken from their presentations and publications
…for their support in discussing the topics, which are presented, and for the provision of informationmaterial and measurement results, I would like to explicitly thank the following colleagues…:
Angela Saa-Hernandez (PSI)
Andreas Streun (PSI)
Matsamitsu Aiba (PSI)
Michael Böge (PSI)
Rasmus Ischebeck (PSI)
Gian Luca Orlandi (PSI)
Gero Kube (DESY)
Minjie Yan (DESY)
Karsten Holldack (HZB – BESSY)
Ake Andersson (MaxLab)
Toshiyuki Mitsuhashi (KEK)
Alan Fischer (SLAC)
Henrik Loos (SLAC) and many more…!!!
…this presentation is far from being complete ! It tries to give an overview of state-of-the-art systemswith a number of – hopefully instructive – examples and (latest) measurements
…important issues e.g. about the design and resolution limitations of optical systems had to be left out!
Motivation for Profile Measurements at SR Light Sources ISpectral Brilliance B is one of the key parameters for SR light sources
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
yyxx
photons
yx
beamNI
B
~~
horizontal beam size
x x x x 2
yxyx ,,
for „flat lattices“ (low coupling) with hy ≈ 0
y y y
use locations for sx meas. with dispersion hx = 0b-functions & dispersion are well known in SR light sources (storage rings)…
→ ex,y can be determined from beam sizes sx,y
Number of Photonssec mm2 mrad2 0.1% BW
vertical beam size
beam divergence
horizontal beam size usually determined by storage ring lattice
vertical beam size is typically minimized by reducing coupling from horizontal to vertical plane
coupling of 0.1 to < 0.01% leads to vertical beam sizes of < 10 µm to a few µm (rms)
Horizontal and Vertical Emittances of Storage Rings
existing () and planned ()
Figure taken from:
R. Bartolini, Low Emittance Ring Design, ICFA Beam Dynamics Newsletter, No. 57, Chapter 3.1, 2012 – and updated.
Motivation for Profile Measurements at SR Light Sources IICoupling Correction @ SLS...:
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Iterative Minimization Procedure → BPM roll error corrections → beam-based girder alignment
→ dispersion & coupling corrections → beam size monitor tuning → random walk optimization
Illustration of SLS Beam Size (short ID straight – 2s)
courtesy of A. Streun M. Aiba, et al., Ultra Low Vertical Emittance at SLS Through
Systematic and Random Optimization, NIM-A 694 (2012) 133-139
Properties of Bending Magnet SR as a Diagnostics Tool
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
SR is non-invasive and “freely available” at light sources
SR covers a wide spectral range from visible to hard X-rays
SR properties & transport are exactly computable (e.g. SRW)
SR is strongly collimated in the vertical plane → but usable opening angle* depends on wavelength
SR main power (heat load) at small opening angle* → (hard) X-ray optical elements require water cooling
SR is emitted with p and s polarization
hard X-ray (@ lc ) opening angle: DY ~ 1/g
opening angle in visible: 3
1
1
c
*
Peculiarities when Imaging with Synchrotron Radiation
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
The object to be imaged is its own source, emitting SR in the forward directiontangential to the circular beam path of the electrons in a bending magnet
SR generates a narrow forward directed cone in the vertical directionand a stripe of light along the mid-plane in the horizontal direction
Imaging situation is similar to a telescope → F-number should be large: F = f / d ≈ 5 m / 30 mm ≈ 165 (SLS case @ 400 nm)
→ Airy-disk radius: rA = 1.22 F ∙ l ≈ 80 µm
spatial resolution limit due to diffraction, when imaging at visible wavelengths
my 802
SLS case: for l = 400 nm and DY = 2.5 mrad
resolution improvements by…: imaging at shorter wavelengths (UV or X-rays)
X-ray pinhole camera
interferometric techniques (UV and/or visible)
Remarks about SR Imaging Systems: Optics, Cameras and Utilities
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
CCD or CMOS cameras are typically used as 2-D sensors / detectors → sufficient sensitivity (high QE), low read-out noise (cooling) and good linearity (visible and UV)
→ data acquisition rates of several kHz, data transfer rates of several hundred Hz
→ small pixel sizes < 5 µm and large number of pixels with RoI selection
SR transfer from X-rays to visible by phosphors (e.g. P43) or YAG:Ce crystals → grain size phosphors and thickness of YAG:Ce crystal might limit resolution
→ saturation effects avoided by attenuation with filters (e.g. Al or Mo for X-rays, NDF for visible)
Imaging quality, measurement resolution and accuracy depends on…: → sufficient magnification of imaging system (e.g. large number of line pairs per mm)
→ sensor / detector size should be ≥ 3 σ of the imaged object
→ sufficiently small pixel sizes and large number of points (pixel) for beam size fit
→ low background noise level and good pointing stability (mech. and thermal stability of set-up)
→ knowledge of optics set-up (e.g. experimental determination of point spread function)
in many cases also applicable to screen monitors
Synchrotron Radiation Monitors: X-Ray Pinhole Camera
courtesy of K.Scheidt, ESRF
P.Elleaume, C.Fortgang, C.Penel and E.Tarazona, J.Synchrotron Rad. 2 (1995) , 209
ESRF ID-25 X-Ray Pinhole Camera
X-ray pinhole camera resolution is limited by:
blurr w L1 L2
12L1
diff 12
4
L2
w
... blurring
... diffraction
Example from ALBA, U. Iriso et al., EPAC 2006
with L1 = 6 mL2 = 12 ml = 12 nm (17 keV)
→ w = 20 mm
typical resolution limitation of x-ray pinhole cameras ~ 10 mm
Example: PETRA III Pinhole CameraØ 18 μm hole in 500 μm thick Tungsten plate
courtesy of G. Kube, DESY
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Synchrotron Radiation Monitors: X-Ray Pinhole Array
W.B. Peatman, K. Holldack, J.Synchrotron Rad. (1998) 5, 639-641
BESSY II X-Ray Pinhole Array
diffraction limited resolution: ~ 11 mm
simultaneous measurement of...: → beam size through single pinhole image
→ beam divergence through envelope
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
IBIC-2012, Tsukuba, October 2nd, 2012Volker Schlott,
Design and Expected Performance of the New SLS Emittance Monitor
T. Mitsuhashi, Spatial Coherency of the SR at the Visible Light Region and its Application for Electron Beam Profile Measurement, Proc. PAC 1997, Vancouver, p. 766
• double slit Michelson interferometer adapted for beam size measurements by Toshi Mitsuhashi• van Citert-Zernike’s theorem relates transverse distribution f(y) via FFT with spatial coherence g(y)
I y0,D I1 I2 sinc a D
Ry0
1 cos
2D
y0
R
Intensity of Interference Pattern
→ spatial coherence
2 I1I2I1 I2
Imax Imin
Imax Imin
provides rms beam size
R D
1
2ln
1
Synchrotron Radiation Monitors: Principle of Interference Monitors
Synchrotron Radiation Monitors: ATF Interference Monitor (with Mirror Optics)
T. Naito and T. Mitsuhashi, Phys. Rev. ST Accel. Beams 9 (2006) 122802
Schematic Set-Up of ATF Interference Beam Size Monitor
Example of an Interferogram Beam Size vs. Shutter Time and Fit of Interferogram
sy = 4.73 ± 0.55 mm
minimal measured beam size:
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Synchrotron Radiation Monitors – Principle of the p-Polarization Method Å. Andersson, et al., Determination of Small Vertical Electron Beam Profile and Emittance at the Swiss Light Source, NIM-A 592 (2008) 437-446
• imaging of vertically polarized SR in the visible / UV
• phase shift of p between two radiation lobes → destructive interference in the mid plane → Iy=0 = 0 in FBSF (filament beam spread function)
• finite vertical beam size → Iy=0 > 0 in FBSF• fringe visibility depends on vertical beam size σy
• modeling by SRW* (Synchrotron Radiation Workshop)
E x,y E 0 sinc2xc p, x
12 1 2K1 3
1
2
c
1 3 2
0
sin2pp, y
d
2-D Electric Field Distribution (in image plane)
2-D Intensity Distribution (in image plane)
I x,y ~ sinc 2 x cos 1
2
with 2 y
O. Chubar & P. Elleaume, Accurate and Efficient Computation ofSynchrotron Radiation in the Near Field Region, EPAC 1998
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Synchrotron Radiation Monitors: SLS p-Polarization Monitor
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
• operating wavelength: variable (266 nm)• opening angle: 7 mradH x 9 mrad V
• finger absorber to block main SR intensity
• imaging by toroidal mirror• magnification: 1.453• surface quality of optics: < 20 nm (l/30 @ 633 nm)
• p-polarization or interferometric method selectable
calibration & alignment
SLS: vertical beam size sy = 3.6 µm ± 0.6 µm for by = 13.5 m → vertical ey = 0.9 pm (natural limit from 1/g: ey,min = 0.2 pm)
Not Treated Here: Imaging SR Monitors with X-Ray (Focusing) OpticsReflective Optics:→ Kirkpatrick-Baez mirror scheme of grazing incidence (q < 0.5°) with pair of ellipsoidal / cylindrical curved mirrors
Example: Advanced Light Source Diagnostics Beam Line
T.R. Renner, H.A. Padmore, R. Keller, Rev. Sci. Instrum. 67 (1996) 3368
Diffractive Optics:→ Fresnel Zone Plates: spacing of rings (e.g. Si, Au) result in constructive interference of light waves in focal point
Examples: X-Ray Beam Imager at Spring-8
S. Takano, M. Masaki, H. Ohkuma, Proc. DIPAC05, Lyon, France (2005) 241 and NIM A556 (2006) 357
Fresnel Zone Plate Monitor at ATF (KEK)
K. Ida et al., NIM A506 (2003) 49 and H. Sakai et al., Phys. Rev. ST Accel. Beams 10 (2007) 042801
Refractive Optics:→ many (30 – 100) Compound Refractive Lenses made from Al or Be for focusing hard X-ray radiation (20 keV)
Example: PETRA III Diagnostics Beam Line for Emittance Measurements
G. Kube et al., Proc. IPAC‘10, Kyoto, Japan (2010), MOPD089, 909
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Coded Aperture X-ray Monitor:→ pseudo-random array of pinholes projects a mosaic of pinhole camera images onto a detector (from x-ray astronomy)
Example: X-ray Monitor at ATF-2 Extraction Line (KEK)
J.W. Flanagan, M. Arinaga, H. Fukuma, H. Ikeda, T. Mitsuhashi, Proc. IBIC’12, Tsukuba, Japan (2012) 237
…and possibly many more!
Excursion: Bunch Compressor Synchrotron Radiation Monitors in FELs
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Energy Spread Measurements with SITF BC SR Monitor Optics Set-Up of SITF BC SR-Monitor
SwissFEL Test Injector BC Layoutmovable bunch compressor chicane
One Motivation for Transverse Profile Measurements in FELs
High Electron Beam Density is required for best FEL performance
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
gain length with FEL parameter
and efficient energy transfer from electron beam to photon beam
depends (among others) on transverse beam sizes and normalized emittances
LCLS Example: Gain Length vs. Emittance E-XFEL SASE-1: Saturation Length vs. Emittance and Wavelength
D.H. Dowell, et al., LCLS Drive Laser Shaping Experiments, Proc. FEL’09 463
R. Brinkmann, et al., Possible operation of the European XFEL with low emittance beams, NIM-A 616 (2010) 81-87
SwissFEL ARAMIS: Gain Length vs. Emittance
courtesy of Sven Reiche
Transverse Profile Measurements in Free Electron Lasers
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Non-invasive SR monitors can only be used in chicanes (e.g. BCs, switchyards, collimators)
→ use screen monitors (2D, destructive) and/or wire scanners (1D, partially destructive)
OTR or scintillator screens are used in diagnostics sections and for matching control
→ sliced and projected emittance and energy spread measurements
wire scanners might be used for online beam size / emittance monitoring in LINACs
Typical transverse beam profiles to be measured in FELs (e.g. SITF, PSI)
…and a comparison
to the «real world»
Scintillator Screens as 2D Transverse Profile Monitors
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
electronbeam
scintillator
camera
Schematic Set-Up and Main Properties of Scintillators as Screen Monitors
electrons passing the scintillator crystal excite atoms and molecules
multiple scattering in scintillator crystal increases beam divergence
visible light from scintillator crystal is radiated in 4p
photons are created along the beam pass through scintillator crystal
thickness of scintillator crystal and observation angle affect resolution
scintillator crystals are very sensitive and radiation resistant
Study of Scintillator Crystals as Transverse Profile Monitors (Gero Kube et al. @ MAMI, Mainz)
Horizontal and Vertical Beam Sizes for Different Scintillator Crystals & Thicknesses Horizontal and Vertical Beam Sizes in BGO for Different Observation Angles
G. Kube, et al., Resolution Studies of Inorganic Scintillation Screens for High Energy and High Brilliance Electron Beams , Proc. IPAC 2010, Kyoto, Japan, 906
Scintillator Properties see e.g.: http://scintillator.lbl.gov/ or http://www.crytur.cz/pages/33/scintillation-materials-data
Optical Transition Radiators as 2D Transverse Profile Monitors
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Schematic Set-Up and Main Properties of OTR as Screen Monitors
OTR is generated when relativistic charged particles pass the boundary of two media with different dielectric (optical) properties
incoherent Optical TR provides good linearity for profile measurements
OTR is radiated in forward and backward direction with an angle of 1/g
surface quality of OTR screen affects profile imaging quality (beam size)
OTR is widely used as beam profile monitors in LINACs
OTR screen could be thin metal foil or silicon wafer (with Al layer)
electronbeam
OTR foil
camera
Q = 1/g
backwardOTR
forwardOTR
H. Loos, et al., Observation of Coherent Optical Transition Radiation in the LCLS LINAC, SLAC-PUB-13395, September 2008
BUT…: Coherent OTR has been observed for highly highly brilliant electron beams
Coherent OTR images from LCLS showing full saturation of camera Coherent OTR was first observed at LCLS
SACLA and FLASH validated COTR observations
LCLS: Profile Measurements with Wire Scannersbut only 1D…
COTR Suppression: Temporal Separation with Scintillator & Gated CCD
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
OTR is an instantaneous process
Scintillation has a “long” decay time
Coherent OTR occurs in case of micro-bunching
Scintillation is insensitive to micro-bunchingelectron buncharrives at screen
t0
time
OTR: t ~ fs - ps
scintillation: t ~ 100 ns
ICCD gating time
COTR Mitigation Tests @ FLASH using Scintillator and ICCD (Minjie Yan et al. @ FLASH, Hamburg)
no delay at ICCDCOTR and CSR on OTR screenCOTR and CSR on scintillator (LuAG screen)
100 ns delay at ICCDno signal from OTR screenScintillation light only from LuAG screen
M. Yan et al., Suppression of Coherent Optical Transition Radiation in Transverse Beam Diagnostics by Utilizing a Scintillation Screen with a Fast Gated CCD Camera Proc. DIPAC 2011, Hamburg, 440
COTR Suppression: Spatial Separation – Central Mask in Imaging System
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
OTR is emitted at an angle Q ~ 1/g
scintillation light is emitted in 4p
at beam energies > 1 GeV (e.g. SACLA BC-3): Q < 0.5 mrad
central mask in imaging system successfully suppresses COTR intensity
(C)OTR emission for small (10 µm) beam sizes at Q ~ l/2s ≈ 100 mrad
SACLA COTR image behind BC-3
S. Matsubara et al., Improvement of Screen Monitor with Suppression of Coherent OTR Effect for SACLA, Proc. IBIC 2012, Tsukuba, Japan, 34
COTR Mitigation @ SACLA using Scintillator and Spatial Mask (S. Matsubara et al., Spring8, Japan)
Image of vertically focused beam behind SACLA BC-3 (full compression)
COTR Suppression: Spatial Separation – SwissFEL Profile Monitors
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
entire screen (large RoI) can be observed without depth-of-field issues by following Scheimpflug imaging principle
observation of beam profile according to Snell’s law of refraction
detector (CMOS sensor) is tilted by 15° for 1:1 imaging to avoid astigmatism
beams can be imaged, which are smaller than scintillator thickness
use YAG or LuAG scintillator crystals instead of OTR
SwissFEL SCM resolution test with 10 pC
rms beam size: 8 µm
Coherent OTR Measurements with SwissFEL SCM at LCLSto be published by R. Ischebeck et al. at IBIC 2014, Monterey, USA
COTR suppression tests at LCLS (full compression, 20 pC)
COTR Mitigation for SwissFEL Screen Monitors (R. Ischebeck et al., PSI, Switzerland)
SwissFEL Screen Monitor Designpatent pending
Summary
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
SR Monitors are used for non-invasive transverse profile measurements at light sources
Different SR Monitor types cover wide spectral ranges from the visible to hard X-rays
Spatial resolutions in the order of a few µm have been achieved for vertical beam sizes
High resolution SR monitors are required for “next generation light sources” where low emittance lattices (few 100 pmrad) and low coupling (< 0.01 %) in higher brilliances
Screen Monitors provide 2D transverse profile information in FELs (LINACs) → determine projected & “sliced” emittances and energy spread → optimize matching into LINACs, transfer and undulator lines
µm resolutions have been achieved even for low beam charges (few pC)
Coherent OTR from highly brilliant beams or beam with micro-bunching structures
Solutions for COTR suppression have been worked out and presented: → temporal separation (gated ICCD) → spatial separation (spatial mask or special observation geometries) → wire scanners as 1D profile monitors have not been presented due to limited time
3rd Topical oPAC Workshop on Beam Diagnostics, May 8 th - 9th, 2014Volker Schlott,
Profile Measurements for Light Sources and FELs
Thank you for your attention…!!!
…and I hope you feel motivated to continue working on these beam dynamics and diagnostics issues for a an even «brighter» future of SR Light Sources and FELs
Further Reading / Information…:
• US Particle Accelerator Schools on Beam Diagnostics using Synchrotron Radiation (2008 and 2010) http://uspas.fnal.gov/materials/08UCSC/UCSC_BeamDiagn.shtml http://uspas.fnal.gov/materials/10UCSC/UCSC_BeamDiagnostics.shtml
• CERN School on Beam Diagnostics (2008) https://cas.web.cern.ch/cas/France-2008/Lectures/Dourdan-lectures.htm
• Workshop on Scintillating Screen Applications in Beam Diagnostics http://www-bd.gsi.de/ssabd/proceedings.htm