Measurements with SwissFEL Transverse Profile Imager at LCLS

Measurements with SwissFEL Transverse Profile Imager at LCLS
PAUL SCHERRER INSTITUT
Profile Monitor YAGS:LTU1:743 12−Mar−2014 02:53:17
2000
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observer
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0
s
virtual image
d
scnitillating
crystal
primary beam
Measurements with SwissFEL Transverse Profile Imager at LCLS
Rasmus Ischebeck, Patrick Krejcik, Henrik Loos, Minjie Yan
Problem: Coherent Optical Transition Radiation (COTR)
> Traditionally, we use optical transition radiation monitors to measure beam profile
Optical Transition
Radiation
> Coherent
Highly compressed
beams emit
coherent radiation that disturbs the measurement
> First observed at LCLS, meanwhile
enhancement also at FLASH and SACLA:
Up to X100,000
observed
OTR11, OTR21 inserted, no coherence
OTR
No upstream screens, X10,000 less attenuation
<- COTR
<- OTR
COTR
SLAC
11
FLASH
Joe Frisch, SLAC
OTR
COTR spikes at APS Injector,
at 2X
minimum bunch length
(Lumpkin et. al. Zeuthen m April 08.)
Yuji Otake, SACLA
Rasmus Ischebeck
COTR
COTR at DESY/FLASH
At max compression 12
SACLA
2
Solution: Use Scintillator, Direct COTR Away from Camera
> Transverse profile imager developed at PSI directs COTR away from the camera:
(coherent)
OTR
to camera
observer
ideal
observation
angle
> At the same time, it achieves a good spatial resolution:
s
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.
(Patent pending)
Rasmus Ischebeck
scnitillating
scintillating
crystal
virtual image
virtual image
aligned with
beam axis
d
primary beam
3
Measurements Performed in December 2013
LCLS Linac-to-Undulator Line
> Beam energy: up to 14.7 GeV
> Bunch charge: 20…250 pC
> Bunch length: 3…70 fs
> Normalized emittance: 300…1600 nm
> Repetition rate: 1…120 Hz
Rasmus Ischebeck
4
Alignment was Improved
> Mis-alignment resulted in large
losses when screen was inserted
> Could be corrected with adjustment
screws
( 102 )
±0.5 ( M o n t a g e m a s s )
165
( 222.5 )
B-B
M 1:2
ter Cube
Anschlagfläche
an Cube
Rasmus Ischebeck, A Transverse Profile Imager for SwissFEL
100
90
5
µ-Bunching Landau Damped by Laser Heater
Ti:saph
758 nm
<15 MW
Injector at 135 MeV
0.5-m undulator
‘Laser heater’ suggested by Saldin et al., NIMA, 2004;
independently by J. Galayda
LCLS design study: Z. Huang et al., PRST 2004
(chicane suggested by T. Smith)
14 GeV With Laser Heater
14 GeV Without Laser Heater
FEL2009, Liverpool, UK
August 26, 2009
Elegant simulations
6
Zhirong Huang
zrh@slac.stanford.edu
Measurements — December 2013
> First Measurements at LCLS show no sign of coherent OTR on the camera:
Profile Monitor YAGS:LTU1:743 04−Dec−2013 18:46:44
0
Laser heater ON:
y (mm)
−0.5
−1
−1.5
−2
−2.5
−6
−5.5
−5
−4.5 −4
x (mm)
−3.5
−3
−2.5
Profile Monitor YAGS:LTU1:743 04−Dec−2013 18:47:36
0
Laser heater OFF:
y (mm)
−0.5
−1
−1.5
−2
−2.5
−6
Rasmus Ischebeck, A Transverse Profile Imager for SwissFEL
−5.5
−5
−4.5 −4
x (mm)
−3.5
−3
−2.5
7
More Measurements — March 2014
> Patrick Krejcik, Henrik Loos (SLAC), Minjie Yan (DESY)
> Quadrupole scans to measure emittance
> First attempt at slice emittance measurement
(1)
(2)
(3)
(1) mapping of the time axis onto the vertical angle by the transverse deflecting strucutre, (2)
variation of the horizontal phase advance between the deflector and the profile monitor by
adjusting the quadrupole lenses, while keeping the vertical phase advance approximately
Rasmus
Ischebeck,
A Transverse
Profile Imager
for is
SwissFEL
8
constant
such
that a vertical
angle
transformed into a vertical position, and (3) measurement
Emittance quad scan at screen
Use tweaker quad
for scan
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X
FODO lattice off
Beta match X and Y waist at screen (almost)
Rasmus Ischebeck
Patrick Krejcik 9
Comparative wire scans less accurate in non-FODO lattice with
waist at screen
X
Screen 2.4
Wire 1.2
!
!
!
Y
Screen 1.6
Wire
1.2
Rasmus Ischebeck
X
Patrick Krejcik 10
Camera Intensity during waist scan
Camera intensity constant versus beam area σx* σy
Looks okay with LH on and under compressed
X
Rasmus Ischebeck
Patrick Krejcik 11
Camera intensity versus laser heater power
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X
Fixed spot size
10% change in camera intensity with LH off
Looks good, so far.
Rasmus Ischebeck
Patrick Krejcik 12
Chirp Scan
Setting A: 20pC, 4.18GeV Setting B: 20pC, 13.1GeV Setting 3: 150pC, 13.1GeV Chirp Scan: Laser Heater ON vs. OFF
X
X
Normalized to mean(Icamera)
•
•
•
•
•
X
Normalized to mean(Icamera)
Scanned from under compression to over compression Camera intensity in the same level for both LH ON/OFF, when the bunch was longer Small enhancement in camera intensity @ Peak compression of -­‐2900 LaserHeater ON: no COTR (maximum enhancement of ~5%) LaserHeater OFF: maximum enhancement of ~10% @ peak compression
Rasmus Ischebeck
Minjie Yan 13
Chirp Scan
Setting A: 20pC, 4.18GeV Setting B: 20pC, 13.1GeV Setting 3: 150pC, 13.1GeV Chirp Scan: Laser Heater ON vs. OFF
X
X
X
Normalized to mean(Icamera)
Normalized to mean(Icamera)
• LH on: no COTR • LH off: only enhancement of factor ~1.2 at peak compression Rasmus Ischebeck
Minjie Yan 14
Chirp Scan
Setting A: 20pC, 4.18GeV Setting B: 20pC, 13.1GeV Setting 3: 150pC, 13.1GeV Chirp Scan: Laser Heater ON vs. OFF (ROI is reduced to a smaller area excluding the stripe pattern)
X
X
X
• With reduced ROI, beam sizes can be determined more precisely. • Up to Ipeak=5000A, no COTR and good agreement with LH off and on. • LH on: in the worst case at peak compression, an enhancement of factor ~2
Rasmus Ischebeck
Minjie Yan 15
A More Detailed Look at the Images
> Features observed to the left of the beam
> Possibly coherent optical diffraction radiation from the mirror edge
Profile Monitor YAGS:LTU1:743 12−Mar−2014 02:53:17
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.JSSPSGBDF
↗︎
↗
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$IBNGFS
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x (Pixel)
500
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Rasmus Ischebeck, A Transverse Profile Imager for SwissFEL
0
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Summary
> SwissFEL transverse profile imager prototype has been successfully installed at
LCLS linac-to-undulator line
> Alignment issues could be fixed in December 2013
> More systematic measurements performed in March 2014
> Possible COTR contribution under nominal conditions (nominal compression, laser
heater on):
> Low charge (20 pC): not more than 5%
> High charge (150 pC): factor 2 when beam size is minimum
> (Compare to factor 105 with OTR profile monitor)
> Stripes beside the beam could be coherent diffraction radiation from the mirror
chamfer
Rasmus Ischebeck, A Transverse Profile Imager for SwissFEL
17
Thank You…
> Hansueli Walther for the technical design
> The AMI team for manufacturing the components
> Markus Baldinger for the assembly
> Patrick Krejcik for setting up an installation of the PSI profile monitor at LCLS
> Gene Kraft for coordinating the installation > Henrik Loos for support with software and operation of the monitor
> Minjie Yan for measurements
> Zhirong Huang for the slide on the laser heater
> The entire LCLS Operations crew
© 2013 Paul Scherrer Institut
Rasmus Ischebeck, A Transverse Profile Imager for SwissFEL
18
One More Thing…
> Slice Emittance with TCAV3, Laser Heater off, Ipk = 750 A
X
Rasmus Ischebeck
Preliminary!
Patrick Krejcik 19
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