Transcript Undulator / FEL Diagnostics

Undulator / FEL Diagnostics
Bingxin Yang
Argonne National Lab
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Undulator / FEL diagnostics scope
Electron beam diagnostics in the undulator
RF BPM (beam centroid)
OTR imager (beam profile)
Wire scanner (beam profile)
Cherenkov counters (beam loss)
Low-power x-ray diagnostics (R&D)
Intra-undulator x-ray diagnostics
Far-field undulator x-ray optics / detector systems
Specifically designed to aid the commissioning and
tuning of the undulator systems.
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Contents
Past conceptual developments and current
plan
Intra-undulator diagnostics: design and R&D
activities in FY2004
R & D for far-field x-ray diagnostics
Conclusions
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Evolution of the x-ray diagnostics plans
CDR (Apr. 2002)
(ANL) Diagnostics for FEL start up in the undulator
(LLNL) Diagnostics for x-ray beam out of the undulator
Re-examination
(Jan. 2004, UCLA) Undulator commissioning workshop
(Feb. 2004, SLAC) X-ray diagnostics planning meeting
(Sep. 2004, SLAC) Diag. and commissioning workshop
Major issues
Beam damage of optical components
Getting sufficient information for FEL tuning?
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Major issues at UCLA workshop
Beam damage of optical components
Example from Marc Ross’ coupon test (LINAC 2000)
Saturated FEL beam deposit even higher energy density
Desirable information
Trajectory accuracy (Dx~1mm)
Effective K (DK/K ~ 1.5×10-4)
Relative phase (Df~10º)
Intensity gain (DE/E~0.1%, z-)
Undulator field quality
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
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Rethink x-ray diagnostics (Galayda)
Intra-undulator diagnostics
Electron beam position monitor (RF BPM)
Electron beam profiler (OTR & wire scanner)
Beam loss Monitor
Low power x-ray Intensity measurements (R&D)
Far-field low-power x-ray diagnostics (R&D)
Clean signature from spontaneous radiation
Space for larger optics / detectors
Single set advantage (consistency, lower cost)
Goal = obtain “desirable information”
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
LCLS Undulator hall schematic
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
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Intra-undulator diagnostics (short breaks)
Location: short breaks (482 mm × 22)
Diagnostics components
RF BPM (work to start in FY05)
Cherenkov detector (work to start in FY05)
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
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Intra-undulator diagnostics (long breaks)
Location: long breaks (909 mm × 10)
Diagnostics components
RF BPM, Cherenkov detector
OTR profiler, wire scanner
x-ray diagnostics (intensity / profile)
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
FY04 activities: diagnostics chamber
Chamber length: 425 mm
Layout of diagnostics chamber
Sharing space side-by-side
OTR profiler
Wire scanner
X-ray diagnostics provision
Double crystal optics
Integrating detector (intensity)
Imaging detector (distribution)
Smooth bore pass-through
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
FY04 activities: OTR camera module
Modular design
Camera module design complete
Waiting for funds to make prototype
Features
Commercial 2 inch lens tube, magnification
adjustable with change of lens
Integral tungsten shield
Stepper driven remote focus
Digital video camera, 30-fps at 1 MP, or 120
fps at VROI (250L), programmable gain.
Manual iris control
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
FY04 activities: wire scanner
Based on SLAC design. Adapted for tighter space.
Features
Mounted on 8-inch flange
On-axis drive mechanism in air
Share space with other diagnostics (OTR and x-ray)
Wire card to adapt SLAC design
A motor-in-vacuum design is being evaluated
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
FY05 plan for intra-undulator diagnostics
Complete and test OTR profiler prototype
Fabricate prototype
Bench test (resolution) and APS(?)/FFTB beam test
Performance review and plan production
Complete and test wire scanner prototype
Compatibility test of in-vacuum motors
Fabricate prototype
Bench test (accuracy) and APS(?)/FFTB beam test
Performance review and plan production
Continue x-ray diagnostics R&D
Start work on RF BPM (cavity type)
Start work on Cherenkov detector
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Far-field x-ray diagnostics: essential elements
Roll away undulators
Spontaneous radiation is most useful when background is
clean, with each undulator rolled in individually.
Adequate far-field x-ray diagnostics
to extract the beam / undulator information:
– Electron trajectory in undulators (1 mm / 0.25 mrad accuracy)
–
–
–
–
Undulator K-value (DK/K ~ 1.5 × 10-4)
Relative phase of undulators (Df ~ 10°)
X-ray intensity measurements (DE/E ~ 0.1%, z-dependent)
Micro-bunching measurements (z-dependent)
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Far-field measurement of FEL gain (z)
Measure monochromatic x-ray beam intensity as undulator
segments are added, characterize the FEL start up and
early gain process
ENERGY RESOLUTION
OF ASYMMETRICALLY CUT Ge(111)
Wide bandwidth mono
(DE/E ~ 0.1%)
Large dynamic range
detector(s)
= 21.5°
= 15°
0.0015
DE/E
Multilayer reflectors
Asymmetrically-cut
crystals
0.0020
0.0010
= 26.5°
= 12.5°
= 18°
0.0005
 = 0 (DEG)
0.0000
3000
4000
5000
6000
7000
PHOTON ENERGY (eV)
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
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8000
Effective K measurement with angleintegrated undulator spectrum
The angle-integrated spectrum has a distinct, sharp
edge at all odd-order harmonics
How can we make use of this
feature to measure effective K?
INTENSITY SPECTRUM OF AN LCLS UNDULATOR SEGMENT
THROUGH A 100 mRAD SQUARE WINDOW
1.4x106
FLUX (PHOTONS/nC/0.01%BW)
X-ray intensity is very sensitive to
effective K changes. For w1
DF/F ~ 400 DK/K
 detect < 6% intensity change.
Only 1 – 2 sec. to acquire data
1.2x106
1.0x106
800.0x103
K=3.499
600.0x103
K=3.501
400.0x103
200.0x103
8200
8250
8300
PHOTON ENERGY (eV)
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
8350
Angle integrated spectrum is robust
Beam of interest is within 35 mrad cone angle
Spectra independent of aperture size / location as long
as the beam is fully contained in the detector.
Spectra independent of emittance for adequate aperture.
1.4
APERTURE
= 160 mrad
1.2
35 mrad
1.0
0.8
0.6
C
B
30 mrad
20 mrad
15 mrad
10 mrad
0.2
K = 3.5000
E = 13.64 GeV
8050
8100
E=8266(eV)
60000
0.4
8000
A
INTENSITY PROFILES IN MOMENTUM SPACE
FLUX (ARB. UNITS)
FLUX (106 PHOTONS/nC/0.01%BW)
UNDULATOR SPECTRA THRU SQUARE WINDOW
8150
8200
8250
8300
PHOTON ENERGY (eV)
October 12, 2004
Undulator / FEL Diagnostics
8350
8400
40000
E=8295(eV)
E=8210(eV)
20000
0
-30 -25 -20 -15 -10
-5
0
5
10
15
20
ANGLE (MICRO-RADIAN)
Bingxin Yang
[email protected]
25
30
Impact of electron bunch fluctuations!!
C
A
B
1.4
1.2
1.0
0.8
0.6
6
X-ray intensity fluctuates proportionally
with electron bunch charge (10-20%).
Electron beam energy jitter (DE/E ~
0.1%) has the same effect as DK/K!
FLUX (10 PHOTONS/nC/0.01%BW)
MODEL UNDULATOR SPECTRA
0.4
0.2
K = 3.5000
E = 13.64 GeV
WINDOW > 50 mrad
8000
8100
8200
8300
8400
PHOTON ENERGY (eV)
Differential measurement cancels beam jitter
• Shoot e-beam through two undulator segments. Intensities
of both x-ray beams fluctuate together as e-beam jitters.
• Taking their difference removes the effect of jitter.
• Signal is proportional to DK of the two undulator segments.
• A very high resolution (<10-5) can be obtained.
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Differential Measurements of Two Undulators
Insert only two segments from
the entire undulator.
Kick the e-beam to separate
the x-rays
Use one mono to pick the
same x-ray energy
Use two detectors to detect
the x-ray flux separately
Use differential electronics
to get the difference in flux
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
A simulation: input and approach
ELECTRON BUNCH CHARGE BY SHOT
ELECTRON BUNCH CHARGE HISTOGRAM
2.0
MEAN = 1.001 nC
STDEV = 0.201 nC
400
1.5
FREQUENCY
BUNCH CHARGE (nC)
500
1.0
300
200
0.5
100
0.0
100
200
300
400
0
0.0
500
0.5
BUNCH NUMBER
ELECTRON BUNCH ENERGY CENTROID
1.5
2.0
ELECTRON BUNCH ENERGY HISTOGRAM
500
13.58
13.60
BUNCH ENERGY (nC)
1.0
BUNCH CHARGE (nC)
MEAN = 13.640 GeV
STDEV = 0.0137 GeV
400
FREQUENCY
13.62
13.64
13.66
13.68
300
200
100
13.70
0
100
200
300
400
500
13.58
13.60
A
B
500
1.2
FREQUENCY
0.8
0.6
0.2
13.66
13.68
13.70
MEAN = 8265.3 eV
STDEV = 16.6 eV
400
1.0
0.4
13.64
NOMINAL PHOTON ENERGY HISTOGRAM
1.4
6
FLUX (10 PHOTONS/nC/0.01%BW)
C
13.62
BUNCH ENERGY (GeV)
BUNCH NUMBER
MODEL UNDULATOR SPECTRA
K = 3.5000
E = 13.64 GeV
WINDOW > 50 mrad
8000
8100
8200
300
200
100
8300
8400
PHOTON ENERGY (eV)
October 12, 2004
Undulator / FEL Diagnostics
0
8200
8220
8240
8260
8280
8300
NOMINAL PHOTON ENERGY (eV)
Bingxin Yang
[email protected]
8320
Differential measurements: simulation
C
A
We can also use it to detect
minor radiation damage!
DK/K =  10-5 !
HISTOGRAM OF DIFFERENCE COUNTS
PHOTON ENERGY = 8265.7 eV
6
TOAL COUNTS = 0.644  10
N_avg = 64 (bunches)
B
1.4
1500
K = 3.499965
K = 3.500035
FREQUENCY
1.2
1.0
0.8
0.6
1000
6
FLUX (10 PHOTONS/nC/0.01%BW)
Select x-ray energy at the edge (Point A).
Record difference in flux from two
undulators.
Boxcar average of 64 points
Peaks for effective K above and below the
reference
value are distinctly resolved
MODEL UNDULATOR SPECTRA
0.4
0.2
500
K = 3.5000
E = 13.64 GeV
WINDOW > 50 mrad
8000
8100
8200
0
8300
PHOTON ENERGY (eV)
October 12, 2004
Undulator / FEL Diagnostics
8400
-8
-6
-4
-2
0
2
4
3
6
DIFFERENCE COUNTS (10 PER BUNCH)
Bingxin Yang
[email protected]
8
Generation of coherent x-ray transition radiation
(Alex Lumpkin, LCLS diag. & comm. Workshop, 9/04)
Coherent XTR peaks ~ 5 mrad
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
CXTR intensity measures micro-bunch fraction
(Alex Lumpkin, LCLS diag. & comm. Workshop, 9/04)
~ 106 photons/nC
Dynamics @ saturation
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Incoherent XTR to be tested in SPPS in FY05
(Alex Lumpkin, LCLS diag. & comm. Workshop, 9/04)
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Far-Field measurement of x-ray beam centroid
Use center of the far-field pattern to determine e-beam
trajectory and slope (x, x’) inside the undulator.
Need relative accuracy 0.25 mrad or better.
Electron Trajectory in LCLS Undulator Prototype
INTENSITY PROFILES IN MOMENTUM SPACE
2.0
x (mm)
1.0
Dx'(in)
Dx(in)
Dx'(out)
0.0
Dx(out)
-1.0
-3.0
-2.0
-1.0
0.0
z (m)
October 12, 2004
Undulator / FEL Diagnostics
1.0
2.0
3.0
FLUX (PHOTONS/nC/0.1%BW)
(Trajectory data from Roger Dejus 1/29/2004)
120x1012
E=26795(eV)
E=26695(eV) +0.4 urad
100x1012
80x1012
E=8164(eV)
60x1012
40x1012
E=8264(eV)
20x1012
0
-15
-10
-5
0
5
10
ANGLE (MICRO-RADIAN)
Bingxin Yang
[email protected]
15
Far-field measurement of relative phase of undulators
Use interference of radiation from two undulators to
tune their phase differences
Relative accuracy ~ 10 degrees or better
Reformulate the question for distributed phase shift?
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Summary of FY04 effort
in far-field x-ray diagnostics
In the new R&D plan, Argonne is a part of the
(SLAC/LLNL/ANL) collaboration on x-ray
diagnostics: concept development, performance
simulation, and system design.
Developed a differential technique for high
resolution measurement of undulator effective K.
Developing micro-bunching diagnostics concept
and planning initial tests.
Developing concept for broadband mono for zdependent x-ray intensity measurements
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
R&D plan for x-ray diagnostics in FY05
Test broadband mono elements (DE/E ~ 0.1%)
Critical to FEL diagnostics inside / outside of undulator
Multi-layer optics and asymmetrically cut crystals
Far-field undulator radiation diagnostics
Continue to identify suitable spatial-spectral features for
FEL start-up x-ray diagnostics
Simulation with non-ideal beam and non-ideal field
Develop x-ray optics / detector requirements
Test core optical components
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]
Conclusions
Plan for start-up x-ray diagnostics has been restructured,
driven by the need of FEL tuning and existing experimental
limitations. Center of gravity shifts significantly towards the
end of undulators. Goals are clearly specified.
With roll away undulators, we have, at least conceptually, a
good handle on measurements of undulator K-value, x-ray
intensity gain, and micro-bunching.
Concept for relative measurements of trajectory direction
(field quality) and undulator phasing need further
development for practical use.
Intra-undulator diagnostics design is nearly on-target.
Funding delays have had severe impact on prototype
schedule.
October 12, 2004
Undulator / FEL Diagnostics
Bingxin Yang
[email protected]