1. LCLS Lehman Review February 7-9, 2005
X Ray Diagnostics
LCLS Lehman Review
February 7-9, 2005

2. FEE Contains Attenuators, Diagnostics, and FEL Offset Mirror System
Be Mirrors 2 & 3
Slit
Diagnostics
Package
Collimator 1
Solid
Attenuator
Fast
close
valve
Gas Attenuator
Ion Chamber
Ion Chamber
SiC Mirror 1
SiC Mirror 2

3. Raw LCLS Beam Contains FEL and Spontaneous Halo
3 mJ High energy core Eg > 400 keV
2-3 mJ (0.3 W) FEL
20 mJ (2.4 W) Spontaneous
Spontaneous halo has rich spectral and spatial structure:
20 mm
0 < E < 10 keV
7.6 < E < 9.0 keV
10 < E < 20 keV
20 < E < 27 keV
At entrance to Offset Mirrors, FEL tuned to 8261 eV Fundamental, 0.79 nC

4. Avoid Damage By Staying Below Melt
Dose along the beam line for different materials
(under normal illumination)
Shown is the maximum dose (over Ephoton=827 to 8267eV)
SiC melt
Si melt
(maximum over eV)
Dose (eV/atom)
B4C melt
Be melt
SiC Mirror - 1/9 melt
B4C PPS - 1/12 melt
Be Solid Attenuator - 1/50 melt
z (m from end of undulator)

5. 15 single shots at each attenuator setting
Experiment Executed at the TTF VUVFEL to Verify SiC and B4C Damage Threshold
C Mirror
Linac
Undulator
Gas Attenuator
Gas Detector
Focusing Mirror
Sample
Samples:
Bulk SiC
Bulk B4C
Thin Film SiC
Thin Film B4C
Thin Film a-C
Bulk Si
Thin Foil Al
TTF VUV Beamline
15 single shots at each attenuator setting
The TTF photon energy of 39 eV is strongly absorbed in C resulting in extreme energy deposition in small volumes.

6. Measured crater depths scale with measured pulse energy
Nomarski picture of ~ 30 micron diameter crater in SiC induced by FEL at 8 x melt
Crater depths, if any, were measured by Zygo interferometry
Pulse-energy measurement below Enominal=1mJ is very noisy.
Therefore, we determined the single-shot pulse energy below 1mJ statistically from the pulse energy statistics at pulse energies ≥ 2mJ

7. Statistical analysis shows damage threshold
15 shot series shot-to-shot relative pulse energy measurements ordered in increasing energy / pulse
Measured crater depths for 2 low fluence 15 shot series, ordered in increasing depth / pulse
Data shows that the shot-to-shot pulse energy varies ~linearly between 0 and 200%
Data shows a consistent damage threshold between 120 and 180 mJ/cm2
No evidence for surface damage below the melt threshold (~ 90 mJ/cm2 to reach Tmelt, ~130 mJ/cm2 to melt SiC)

8. Prioritized List of Desired FEL Measurements
Total energy / pulse l1
Photon wavelength
Dl/l1
Photon wavelength spread
Pulse centroid
Beam direction
f(x,y)
Spatial distribution
su,sl1
Temporal variation in beam parameters t
Pulse duration

9. Prioritized List of Desired Spontaneous Measurements
f(x,y,l1)
Spatial distribution around l1 l1
1st harmonic Photon wavelength
Dl/l1
1st harmonic wavelength spread
Beam direction u
Total energy / pulse
su,sl1
Temporal variation in beam parameters

10. FEE Schematic e- Start of Experimental Hutches Windowless Ion Chamber
Diagnostic Package
5 mm diameter collimators
Solid
Attenuator
Spectrometer / Indirect Imager mirror
High-Energy
Slit
Total
Energy
Calorimeter
FEL Offset mirror system e-
Gas
Attenuator
WFOV Direct Imager
Windowless Ion Chamber
Muon Shield
FEL Spectrometer and Direct Imager in NEH

11. Wide Field of View Direct Imager
Photoelectrons generated by 0.01% FEL
Single shot measurement of f(x,y), x, y ,u
Camera
Scintillators

12. Single shot measurement of f(x,y), x, y, u Multi shot measurement of l
Indirect Imager
B4C/SiC Test Multilayers Fabricated
Single shot measurement of f(x,y), x, y, u
Multi shot measurement of l
Angle selects energy and attenuation

13. Total Energy Calorimeter
Thermal diffusion calculations performed
Single shot measurement of f(x,y), x, y, u
t = 300 ms
t = 100 ms
Nd0.8Sr0.2MnO3
Cold Si substrate
CMR Sensor array 100 pixels
Xray Beam
t = 0 T
Cooling ring
T, ms 5

14. Sensor Development: Nd0.8Sr0.2MnO3

15. Single shot, non destructive, measurement of
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

16. FEL Spectrometer Single shot, measurement of
l with 8.26 keV Transmission Grating Specrometer
Sputter-sliced SiC / B4C multilayer
Interference Function
P = 200 nm
N = 500
D = 100 mm
Single Slit Diffraction Pattern
33 mm thick
Observed Intensity
Beam
100 mm
angle

17. Off-Axis Zone Plate Scintillator Image of 8.26 keV FEL
Positive
Positive Spectra
(Unfocused)
Negative
Negative Spectra
(Focused)

18. Spectrometer measures FEL central Wavelength to < 10-3
-4,000
-4,000
l = nm
l = nm
m = mm
m = mm

19. Using FEL Spectrometer to measure Undulator K*
On axis:
Effect of changing K
But
etc.
* One of several methods under study to measure K

20. Monte Carlo simulation of Transmission Grating in LCLS Beam
Spontaneous Photons generated
From Near-Field Spontaneous Radiation Calculations to energies up to 4 MeV
FEL photons generated from Gaussian FEL Model
Imager
Horizontal Slit
Scintillator
Transmission
Grating
Vertical Slit
photons
All photons tracked through undulator and photon beamline to grating, then to scintillator
Undulator

21. Scintillator Image using spontaneous radiation from First Undulator Segment with Nominal K
Positive Spectra
(Unfocused)
Negative Spectra
(Focused)

22. Measured Spectra of First Segment
Nominal K
K detuned by 10-3
Fitted Centroid:
± 0.06 mm
Fitted Centroid:
± 0.06 mm
53,192 photons in Monte Carlo Simulation
Scaled to Full Pulse: 135,799 ± 588 photons

23. Undulator Segment Spectral Measurements Summary
Spectral Shift Relative Difference = (L-LastNom)/LastNom
L = Data set Fit Centroid
LastNom = Last Segment, nominal K, Fit Centroid
DataSet
Fit Centroid (mm)
Relative Difference
X 104
FirstDet-3
± 0.062
16.9 ± 0.4
FirstDet-4
± 0.062
1.3 ± 0.4
FirstNom
± 0.063
-0.3 ± 0.4
MidDet-3
± 0.083
17.6 ± 0.4
MidDet-4
± 0.083
1.5 ± 0.4
MidNom
± 0.083
-0.2 ± 0.4
LastDet-3
± 0.137
17.3 ± 0.5
LastDet-4
± 0.137
1.6 ± 0.5
LastNom
± 0.062
0.0

24. Diagnostics Summary Instrument Purpose Calibration and Physics risks
Status
Direct Imager
SP f(x,y), look for FEL, measure FEL u, f(x,y), x,y
Scintillator linearity, Attenuator linearity and background
Prototype
Indirect Imager
Measure FEL u, f(x,y), spectral imaging of SP and FEL harmonics, attenuator calibration
Mirror reflectivity, damage
ESD
Total Energy
FEL u
Energy to Heat, damage
Ion Chamber
FEL u, x,y,x',y'
Signal strength
Conceptual
Spectrometers
FEL, SP spectra
Resolution, damage

25. Summary FEL Offset Mirror integrated into FEE layout
TTF Damage Experiment confirms damage thresholds for SiC
Conceptual designs for Imagers, Calorimeter, FEL Spectrometer, and Gas Detector
We are confirming Conceptual designs with our detailed simulation
FEL Spectrometer shows some utility for determining K of undulator segments to 10-4