Vertical Emittance Measurements using a Vertical Undulator
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Vertical Emittance Measurements using a Vertical Undulator
K.P. Wootton, G.N. Taylor, R.P. Rassool
Uni. Melbourne
M.J. Boland, B.C.C. Cowie, R. Dowd, Y.-R.E. Tan
Australian Synchrotron
Y. Papaphilippou
CERN
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2Wootton – CLIC DR Meeting – 13/09/2012
Overview
• Measurement of vertical emittance• Undulator spectra• Photon beam brilliance• Vertical undulators• Measurements of undulator spectra• Future directions
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Vertical emittance
• Collider damping rings and Super B-factory storage rings demand 0.5-2.0 pm rad
• Collective effects lead to growth– IBS, electron cloud
• Storage ring light sources as test accelerators– SLS, ATF2, CESR, ASLS, Diamond, … (ALS?)
• Need measurements of vertical emittance
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Indirect measurement
• Orbit response matrix fitting
• Touschek lifetime– Eigen as opposed to
projected emittances• Beam ellipse tilt (bending
magnet)
Dowd PRSTAB 14, 012804 (2011)
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Direct measurementLaser wire scanner
• Scanning laser waist through electron beam
– Inverse Compton gamma rays
• Shintake monitor– Interference pattern
narrower than laser waist
Shintake NIMA 311, 453-464 (1992)
Boogert PRSTAB 13, 122801 (2010)
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Direct measurementVertical emittance monitors
• Three main approaches:– Imaging– Interferometry– Projection
• Quick diagnostic of storage ring
• Typically bending magnet– $$↓, ↑, ↓
• Visible light, hard x-ray
Andersson, NIMA 591, 437-446 2008
Scheidt, DIPAC05 CTWM01
Masaki DIPAC01, PS17 Flanagan PAC09, TH5RFP048
Nakamura PAC01, TPAH307
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Undulator diagnostics
• Focus on odd (useful!) harmonics
• Horizontal undulators– Imaging– Projection– Absolute spectral brilliance
(pinhole flux)
• Energy spread, dispersion, ‘large’ emittance
Moreno JSR, 19 179-84 (2012)
Hahn JSR 4, 1-5 (1997)
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Undulator beam projection
Undulator25 periods
75 mm periodK = 3.85
Pinhole50 x 50 um
15m distance
Electron beam
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Horizontal undulator Vertical undulator
Undulator projection measurements
Undulator25 periods
75 mm periodK = 3.85
Electron beam
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Photon beam brilliance
• Horizontal undulator– No contrast
• Vertical undulator– Even harmonics
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Photon beam brilliance
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Fitting spectra
• Convolve beam emittance with undulation
• ‘It is evident that the second-harmonic brightness is proportional to the beam emittance …’ Dattoli PRE 52(6) 6809-17 (1995)
• I add to this: … the emittance in the direction of undulations
– How do we measure photon beam brilliance?
Dattoli PRE 52(6) 6809-17 (1995)
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Advanced Planar Polarised Light Emitter-IIModes of operation
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SXR undulator beamline
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SXR undulator beamline
• APPLE-II undulator• White beam slits first optical element• All focussing, monochromator downstream
Slits Monochromator Photodiode
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Detector
• Measuring vertical emittance with one large pixel!
• Beamline optics– Grating monochromator– Au-coated mirrors– Energy-defining slit– Photodiode (GaAsP, Si)
• Au-coated mirrors– Transmission varies with
photon energy
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Photodiode choice
• Early experiments– Hamamatsu GaAsP
• Ratio of peaks• Absorption edges
– Silicon photodiode
• Keithley picoammeter– Spans many orders of
magnitude in current
Krumrey, Tegeler (1992) Rev Sci Instrum 63 (1), p. 797-801
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Horizontal undulator Vertical undulator
Undulator projection measurements
K = 3.85E = 3 GeV75 mm period
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Measured undulator spectrum
• Measured
• Modelled
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Emittance envelopes
• Measured ratio of adjacent peaks
• Fitted envelopes of emittance
– Fitted pinhole size of – minimisation using Matlab
and SPECTRA 9.0
• 0 pm rad– Ratio is non-zero
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Where to?
• Fixed pinhole diameter• SOLEIL DiagOn (fixed
energy 367.5 eV)• SPring-8 BL45XU (vertical
IVU)• Higher undulator k• Lower beam energy (IBS
studies)– Same minimum gap, higher
undulator k
Moreno JSR, 19 179-84 (2012)
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Summary
• Undulator measurement of emittance is an old technique– Usually use horizontal undulator, horizontal emittance– Introduce vertical undulator, vertical emittance
• Measure pinhole spectra for different emittances• Evaluate ratios of adjacent harmonics
– Simulations of undulator flux– Fitted pinhole size of – Knowing pinhole size, would fit for beam emittance
• New vertical emittance measurement for many electron storage rings