Transcript Instrumentation for Linac-based X-Ray FELs Henrik Loos 12

Instrumentation for Linac-based X-Ray
FELs
Henrik Loos
12th Beam Instrumentation Workshop
May 1-4, 2006
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Outline
XFEL introduction
LCLS overview
Electron beam diagnostics
Transverse Beam Properties
Longitudinal Beam Properties
Photon beam diagnostics
3 May 2006
Henrik Loos
BIW 2006
[email protected]
X-Ray FEL Features
~1Å photon wavelength or ~10keV photon
energy
Uses SASE principle to amplify and saturate
spontaneous radiation in ~100m of undulator
Requires
U
2

R  2 1  K rms
2
Multi GeV beam energy
kA peak beam current
Micron beam emittance to match photon beam

phase space

4
3 May 2006
Henrik Loos
BIW 2006
[email protected]
X-Ray FEL Parameters
Electron Beam
LCLS
XFEL
SCSS
Energy
GeV
4.3-13.6
10-20
6.1
Peak Current
kA
3.4
5
3
Bunch Charge
nC
0.2-1
1
1
Norm. Slice Emittance μm
1.2
1.4
0.85
Bunch Length
fs
70
80
80
Slice Energy Spread
MeV
1.4
2.5
0.25
LCLS
XFEL
SCSS
Photon Beam
Saturation Length
m
60-100
40-170
80
Photon Energy
keV
0.8-8
0.2-12.4
12
Peak Power
GW
4-8
22-135
3
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Linac Coherent Light Source
Injector
Undulator
Near Hall
Far Hall
3 May 2006
Henrik Loos
BIW 2006
[email protected]
LCLS Accelerator Layout
6 MeV
z  0.83 mm
  0.05 %
Linac-1
L 9 m
rf  -25°
...existing
linac
21-1
b,c,d
DL1
L 12 m
R56 0
Courtesy P. Emma
4.30 GeV
z  0.022 mm
  0.71 %
13.6 GeV
z  0.022 mm
  0.01 %
Linac-X
L =0.6 m
rf= -160
Linac-0
L =6 m
rf
gun
250 MeV
z  0.19 mm
  1.6 %
135 MeV
z  0.83 mm
  0.10 %
Linac-2
L 330 m
rf  -41°
Linac-3
L 550 m
rf  0°
21-3b
24-6d
25-1a
30-8c
X
BC1
L 6 m
R56 -39 mm
BC2
L 22 m
R56 -25 mm
SLAC linac tunnel
undulator
L =130 m
DL2
L =275 m
R56  0
research yard
3 May 2006
Henrik Loos
BIW 2006
[email protected]
LCLS Diagnostics Tasks
Charge
Toroids (Gun, Inj, BC, Und)
Faraday cups (Gun & Inj)
Trajectory & energy
Stripline BPMs (Gun, Inj, Linac)
Cavity BPMs (Und)
Profile monitors (Inj), compare
position with alignment laser
Bunch length
Cherenkov radiators + streak
camera (Gun)
Transverse cavity + OTR (Inj,
Linac)
Coherent radiation power (BC)
Slice measurements
Horizontal emittance
T-cavity + quad + OTR
Transverse emittance & energy
spread
Wire scanners
YAG screen (Gun, Inj)
OTR screens (Inj, Linac)
Vertical Emittance
OTR in dispersive beam line +
quad
Energy spread
T-cavity + OTR in dispersive
beam line
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Diagnostics Requirements
Parameter
Method
Unit
Resolution
Current
Toroid, FC
%
2
Position
Stripline BPM
μm
5 - 20
Cavity BPM
μm
1
Wire Scanner
μm
5
YAG
μm
15 – 30
OTR
μm
5 – 30
Streak Camera
fs
300
Transverse Cavity
Slices
10
BLM
%
5
Beam Size
Bunch Length
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Cherenkov
LCLS Injector Diagnostics
YAG, FC
YAG
Toroid
T-Cavity
Phase Monitor
Wire Scanner
Toroid
OTR
OTR
YAG
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Toroid
LCLS Linac Diagnostics
6 MeV 135 MeV
rf
gun
Linac-0
L =6 m
4.30 GeV
250 MeV
13.6 GeV
Linac-X
L =0.6 m
Linac-1 BC-1
L 9 m L 6 m
X
21-3b
24-6d
Linac-3
L 550 m
T-Cav
21-1b
21-1d
Linac-2 BC-2
L 330 m L 22 m
25-1a
30-8c
LTU
L =275 m
undulator
Spect.
WS
OTR
WS - Wire Scanner
BLM - Bunch Length Monitor
BLM
SLAC linac tunnel
OTR
WS
OTR
Dump
research yard
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Beam Profile Monitors (YAG & OTR)
YAG requirements
Use 100µm thick crystals to meet resolution
GTF measurements show feasibility
OTR requirements
Optimize yield to enable beam profile measurement at 0.2nC
OTR yield for 100mrad angular acceptance
Energy (MeV)
QE (%), 450-650 nm
QE (%), 400-750 nm
135
0.44
0.75
4300
0.98
1.68
13500
1.17
1.99
Provide sufficient depth of field for imaging of 45° foil
Simulation shows 1mm DOF for f/# of 5 within 20µm resolution
Match direction of reflection with axis of dispersion or T-CAV deflection
Foil is aluminum to optimize TR yield and 1µm thick to minimize radiation
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Optics Layout
CCD
Used for all standard YAG/OTR
screens
Telecentric lens
Filters
Stack of 2 insertable neutral
density filters
Beam splitter and reticule for in
situ calibration
Megapixel CCD with 12bit and
4.6µm pixel
Radiation shielding required in
main linac tunnel
Lens
55mm focal length
>100 line pairs/mm
Magnification up to 1:1
Vacuum
OTR
Beam splitter
Reticule
YAG
e-beam
Illumination
3 May 2006
Henrik Loos
BIW 2006
[email protected]
OTR/YAG Optics Design
Courtesy V. Srinivasan
3 May 2006
Henrik Loos
BIW 2006
[email protected]
OTR Imager with Tilted Geometry
Need wide field of view
in focus for
measurements in
spectrometer beam
line
Tilt OTR screen and
CCD by 5 degrees in
1:1 imaging
10um resolution
B.X. Wang et al. PAC05
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Simulation of OTR Beam Size Measurement
Include 0.5% TR yield, photon
shot noise, and typical CCD
parameters for quantum
efficiency, read out noise, pixel
size, digitizer gain
y (mm)
Simulation of CCD image
Calculation of beam size
Simulation agrees well with OTR
measurement at GTF
Error of 5% in beam size for
beam of 0.1nC, 260µm at 10µm
resolution
0
-2 E = 135 MeV
-2
Counts
Generate beam profile with 10σ
bounding box
Compare rms width of profile
with original Gaussian beam
size
2 Q = 0.1nC
0
2
30
20
10
0
-1
0
x (mm)
3 May 2006
Henrik Loos
BIW 2006
[email protected]
1
Longitudinal Diagnostics
Gun region
Cherenkov radiator & streak camera
Bunch length and slice emittance
Transverse cavity
Longitudinal feedback loop
Integrated power from coherent radiation
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Cherenkov Radiators
Located in gun region for temporal diagnostics of
6 MeV beam from gun
Convert electron beam time structure into light
pulse for streak camera measurement
Cherenkov light suitable at low beam energies
Design requirements
Match time resolution of radiator to streak camera
(Hamamatsu FESCA-200, < 300fs)
Generate and transport a sufficient # of photons for
200pC beam to streak camera in laser room (10m away)
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Cherenkov Radiator Design
Fused silica
n = 1.458, θCR = 46.7°
Total internal reflection
Frosting of back surface
NΦ = 7.5/e/mm/50nm
@400nm
Temporal and spatial
resolution
Thickness of 100µm
Δt = 375fs
Δx = 190μm
e-
CR
2d tan  CR
d
Frosted Surface
Courtesy D. Dowell
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Optical Transport Layout
1:1 relay imaging from
radiator to streak camera
Assume 1% efficiency from
frosting to scatter into
100mrad
6% acceptance through
tube for source of 5mm x
100mrad
1.5·105 photons on slit of
streak camera for 200 pC
Laser Room
Streak Camera
10m long optics tube
50 mm clear aperture
20 surfaces with
95% transmission/surface
mirror reflectivity 75%
100 micron thick radiator
Courtesy D. Dowell
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Transverse Cavity
Electron Beam
Horizontal
Kicker
Vertical
Deflecting Cavity
Off-axis Screen
Translates longitudinal into transverse beam profile
when operating at RF zero crossing
Parasitic operation with kicker and off-axis screen
Single shot absolute bunch length measurement
Temporal resolution limited by unstreaked spot size
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Transverse Cavity Measurement at TTF
Beam without and with BC 3 (second bunch compressor)
13 femtosecond FWHM spike!
1 picosecond
1 picosecond
Scans at high power ~16MW
Courtesy J. Frisch
3 May 2006
Henrik Loos
BIW 2006
[email protected]
TCAV in LCLS after BC2
18
BC2 Charge distribution
OTR_TCAV
16
14
12
Current (kA)
Short 70fs bunch
length requires full RF
power for cavity
Parasitic measurement
with beam optics
optimized for SASE
Resolution 20fs
sufficient for length
measurement
10
8
6
4
2
0
-200
-100
0
Time (fs)
3 May 2006
Henrik Loos
BIW 2006
[email protected]
100
200
Bunch Length Monitor
0.7
dW1  
W  N  d
f  ,
d
2
e
f     nt e d
it
0.6
BC1
16
BC2
14
0.5
12
Current (kA)
Relative bunch length measurement used
for longitudinal feedback
Non-intercepting, calibrated with
interceptive TCAV measurement
Based on integrated power from coherent
radiation source (C*R)
18
0.4
10
0.3
8
6
0.2
4
0.1
0
-2000
2
2
0
Time (fs)
0
-200
2000
0
Time (fs)
BC1 FF
BC2 FF
BC1 Exp
BC2 Exp
1
0.8
Form Factor
Single electron radiation spectrum W1(ω)
depends on radiation source
Bunch length determined by
long wavelengths λ » 2πσrms
BC1: 1cm – 1mm
BC2: 1mm - .1mm
200
0.6
0.4
0.2
0 -1
10
10
0
1
10
Wave Number (cm-1)
3 May 2006
Henrik Loos
BIW 2006
[email protected]
10
2
10
3
Radiation Sources
Wide range of bunch lengths from 25um to 300um
Diode detectors work well below 300GHz
Pyroelectric detectors work well above 300GHz
Long bunches
Couple radiation from ceramic gap in beam pipe into
waveguides with different diode detectors
Short bunches
Extract coherent radiation from bend magnet with hole
mirror and send to a pyroelectric detector
3 May 2006
Henrik Loos
BIW 2006
[email protected]
CER Detector Layout
Edge rad. dominates
over synchrotron and
Pyro-Detector
diffraction
10mm
Lenses, f = 400mm
Near field calculation
necessary for radiation
spectrum at detector
Window
200mm
Bend
e-Beam
50mm
SR
ER
DR 15mm
200mm
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Bunch Length Sensitivity of Detector Signal
Detection efficiency includes diffraction, vacuum window, water
absorption, pyroelectric detector response, and bunch form
factor.
Introduce high and low pass filters at 10cm-1 and 20cm-1.
7
30
26 um
54 um
82 um
111 um
141 um
170 um
200 um
Efficiency (%)
5
4
25
Detector Signal (J)
6
3
2
20
15
10
5
1
0
0
no
hp10
hp20
lp10
lp20
10
20
30
40
-1
Wavenumber (cm )
50
60
0
20
40
60
80
100 120 140
Bunch Length (m)
3 May 2006
Henrik Loos
BIW 2006
[email protected]
160
180
200
Gap Radiation Detector
Expect 2uJ radiation
energy from 2cm gap for
1nC, 200um bunch
(Calculation J. Wu)
Energy density of
1.6nJ/mm2
Diode sensitivity
~0.1pJ/mm2
Disperse pulse in 20cm
waveguide to keep
diodes in linear range
Diodes paired to reduce
dependence on beam
position
Courtesy S. Smith
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Photon Beam Diagnostics
Measure spontaneous radiation for undulator
commissioning
Measure FEL photon beam for SASE
commissioning
Nondestructive measurements of beam
properties for user operation
3 May 2006
Henrik Loos
BIW 2006
[email protected]
LCLS FEE Schematic
Windowless
Ion
Chamber
Diagnostic Package
Spectrometer / Indirect
Imager mirror
Solid
Attenuator
e-
High-Energy
Slit
Gas
Attenuator
Muon
Shield
5 mm
diameter
collimators
Start of
Experimental
Hutches
Total
Energy
Calorimeter
Windowless
Ion
Chamber
WFOV Direct
Imager
FEL Offset
mirror
system
FEL Spectrometer and Direct
Imager in NEH
Courtesy R. Bionta
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Wide Field of View Direct Imager
Photoelectrons
generated by 0.01%
FEL
Horizontal LineOut
Single shot measurement of
f(x,y), x, y ,u
PhotoElectrons/Pixel
400,000
300,000
200,000
100,000
0
-50 -40 -30 -20 -10 0 10 20 30 40 50 60
X, mm
Camera
Y, mm
Fluence
Scintillators
20
15
10
5
0
-5
-10
-15
-20
-60
-40
-20
0
X, mm
20
40
60
Courtesy R. Bionta
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Indirect Imager
B4C/SiC Test Multilayers
Fabricated
Single shot measurement of
f(x,y), x, y, u
Multi shot measurement of 
Angle selects energy and
attenuation
Courtesy R. Bionta
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Total Energy Calorimeter
Thermal diffusion calculations
performed
t = 300 s
t = 100 s
Single shot measurement of
f(x,y), x, y, u
Cold Si
substrate
Xray Beam
Cooling
ring
Nd0.8Sr0.2MnO
3
CMR Sensor
array 100
pixels
t=0
T
0
T, ms
5
Courtesy R. Bionta
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Ion Chamber
Single shot, non destructive,
measurement of
x’, y’, x, y ,u
Segmented
cathodes for
position
measurement
10 cm
1 torr
Imaging of optical
emission for
position
measurement
Courtesy R. Bionta
3 May 2006
Henrik Loos
BIW 2006
[email protected]
Summary
Electron beam diagnostics based on proven
methods
Photon beam diagnostics needs development of
new techniques which are difficult to test due to the
lack of a photon source comparable to an X-FEL
Acknowledgements
Thanks to many colleges from the LCLS
collaboration
3 May 2006
Henrik Loos
BIW 2006
[email protected]