FEL Commissioning Plans
J. Welch, et. al.
Accelerator System Breakout Session
10/30/07
LCLS
October 30, 2007
FAC
1
James Welch
Welch@SLAC.Stanford.edu
Timeline of Installation and Commissioning
FEE/NEH/X-Ray Tunnel/FEH Installation
Linac/BC2
LTU/UND/Dump Installation
Now
1st Spont. Light
1st FEL
Light 1st NEH Light
2008
Controls checkout
& re-commission
Injector
…Injector
Commissioning
2009
Re-commission
Inj/BC2 to SL2
Linac/BC2
Commissioning
PPS
2007
PPS
J A S O N D J F M AM J J A S O N D J F M AM J J A S ON D
FEL/FEE
Commissioning
LTU/Und/Dump
Commissioning
downtime
commissioning
installation
October 30, 2007
FAC
2
James Welch
Welch@SLAC.Stanford.edu
FEE/FEL Commissioning Period
Starts with Xrays to FEE. Ends
with Xrays to NEH.
Pre-requisites: BBA working in
undulator. Electron beam
systems mostly commissioned
from Drive Laser to Beam Dump.
Simultaneous commissioning of
Xray diagnostics and Xray
beam.
2 months shared FEL beam with
Xray diagnostics
1 month shared with Mirror
system
October 30, 2007
FAC
3
James Welch
Welch@SLAC.Stanford.edu
FEL Commissioning - Phase I
(~2 months)
Using SR only
Get “First Light” milestone
Establish optical axis
Commission X ray diagnostics
Characterize SR from individual and multiple
segments
Measure “photon flux” milestone
October 30, 2007
FAC
4
James Welch
Welch@SLAC.Stanford.edu
X Ray Diagnostics
Gas
Detector
5 mm
diameter
collimators
Hard x-ray
Monochromator
(K Spectrometer) Direct Imager
Solid
Attenuator
e-
Slit
Muon
Shield
October 30, 2007
FAC
Gas
Detector Soft Xray
Gas
Imager
Attenuator
Soft X-Ray
Offset mirror
system
NFOV
Total
Energy
Thermal
Detector
WFOV
Hard X-Ray
Offset mirror
system
Start of
Experimental
Hutches
5
James Welch
Welch@SLAC.Stanford.edu
K Spectrometer/Monochromator
1 eV bandpass at
1st harmonic
filters out most of
the spontaneous
radiation
Works only for 8
keV XRays
Si(111)
8.265 KEV SETTING
117
10mm
MAXIMUM
ACCEPTANCE
60
10
80
28
Ø100
TUNGSTEN BEAM STOP
WITH B4C
PROTECTION FACE
STANDARD WIRE-SEAL
FLANGE FOR Ø16" TUBE
Ø497 [Ø19.6]
Ø400
October 30, 2007
FAC
6
James Welch
Welch@SLAC.Stanford.edu
Soft X-Ray Imager
1% bandpass at first harmonic
filters out most of the
Spontaneous radiation.
works only at 800 eV
X-Ray CCD
Camera
Multilayer Mirror:
Resonant Wavelength: 1.5 nm
Relative Bandwidth: 1%
Vacuum
Chamber
October 30, 2007
FAC
7
James Welch
Welch@SLAC.Stanford.edu
“First Light…”
…will be seen on a YAG
screen of the Direct Imager
Shown on right is
calculation of Spontaneous
Radiation hard X-Rays
entering the FEE.
Undulator vacuum chamber
has realistic “rough” walls
for reflection model
Light fills the vacuum
chamber
8 cm x 6 cm
October 30, 2007
FAC
8
James Welch
Welch@SLAC.Stanford.edu
Establish Optical Axis
Want to align gas attenuator and gas detector 3 mm apertures,
fixed mask, and mirror systems, to a common optical axis co-linear
with the xray beam axis.
Need to determine the central ray of Xray beam.
Three possible methods:
1.
Use the K measurement crystal followed by the direct imager to find the spatial
center of the filtered 1st harmonic.
2.
Make a small hole with variable slits and scan the slit center while measuring
the spectrum with the K measurement “spectrometer”. The central ray is
coincident with the maximum spectral shift.
3.
Use the Soft Xray imager and a low energy beam to find the spatial center of
the filtered 1st harmonic. This has been simulated.
October 30, 2007
FAC
9
James Welch
Welch@SLAC.Stanford.edu
Central Ray Using K Spectrometer
~1 eV BW, 8 keV, pinhole.
Fluxview calculation, 1st
segment
Photon Flux [photons/100 um^2/pulse]
Spatial Distribution
40
30
20
10
0
0
2
4
6
8
10
12
Radial Angle [micro-radian]
peak
85% peak
50% peak
15% peak
October 30, 2007
FAC
Off energy
P. Stefan
10
James Welch
Welch@SLAC.Stanford.edu
Finding the Central Ray and SASE
At low energy, use the Soft X-Ray Imager
RAW XRays
October 30, 2007
FAC
1% BW Filtered SR
11
FEL Beam
James Welch
Welch@SLAC.Stanford.edu
Measure SR from Undulator Segments
Measure what?
Central ray position, as above, and relate it to local BPM
readings.
Average spectrum using K monochromator
Spatial profile, using the Direct Imager.
K measurement? Will we have time?
Why?
Provides a basis for future comparisons. Establishes all
segments are producing Xrays as expected and are free from
anomolies.
October 30, 2007
FAC
12
James Welch
Welch@SLAC.Stanford.edu
K Measurement: 2-Segment Scheme
Measure synchrotron radiation spectrum produced by two
undulator segments, and scan K of one segment
Other schemes compare spectra from individual segments.
(Pinhole technique, angle-integrated edge measurement,
reference undulator)
K’s are matched when spectrum has the steepest slope on
high energy side of 1st harmonic peak.
Match segments pairwise until all segments are measured.
undulator segments (33 total)
segments under test
October 30, 2007
FAC
13
James Welch
Welch@SLAC.Stanford.edu
FEL Commissioning - Phase II
(1 month)
Generate and detect FEL Radiation at low energy
Find SASE signal
Measure Gain Curves
Optimize gain
Steer FEL Radiation thru center of C1 5 mm aperture,
then M1-Soft
Change energies when time allows
October 30, 2007
FAC
14
James Welch
Welch@SLAC.Stanford.edu
FEL Measurements
Desirable measurements
as function of position
along undulator :
Saturation
Exponential
Gain Regime
Intensity (LG, Saturation)
Spectral distribution
Bunching
Undulator Regime
Desirable measurements
after undulator :
1 % of X-Ray Pulse
Pulse length
Spatial shape and centroid
Divergence
Electron Bunch
Micro-Bunching
October 30, 2007
FAC
15
James Welch
Welch@SLAC.Stanford.edu
Gain Curve Measurement (1)
1. Trajectory bump method
vacuum chamber
undulator segments (all in)
orbit
kick
FEL Radiation alone is “turned off” by distorting orbit with
a single corrector.
XRays
Spontaneous radiation is more or less constant. If filtered,
FEL will dominate over SR.
October 30, 2007
FAC
16
James Welch
Welch@SLAC.Stanford.edu
Gain Curve Measurement (2)
Variable length undulator method
SR and FEL radiation are both “turned off” by removing segments
October 30, 2007
FAC
17
James Welch
Welch@SLAC.Stanford.edu
Gain Optimization (just words)
beta matching studies
bunch compression studies
laser heater studies
trajectory sensitivity studies
taper studies
...
October 30, 2007
FAC
18
James Welch
Welch@SLAC.Stanford.edu
Offset Mirror Systems
Precision steer the FEL
beam onto the Mirror
system axis and keep it
there.
FEL beam/mirror steering
studiesP
FEL or Mirror axis
Pointing system feedback
commissioning.
P
Get high energy FEL to
work. Stabilize and
improve the beam quality.
Precision steer FEL beam
to center of radiation
protection collimator C1 and
M1-Soft.
Steering feedback?
P
October 30, 2007
FAC
P
P
19
P
James Welch
Welch@SLAC.Stanford.edu
Summary
Plans for intital FEL commissioning are shaping
up.
Diagnostics tools are at, or passed, the concept phase
Methods for finding SASE and the central rays are identified.
Methods for gain curve measurements have been worked out
Overall planned duration is very short
Considerable additional commissioning time will be needed
especially for 0.15 nm radiation.
October 30, 2007
FAC
20
James Welch
Welch@SLAC.Stanford.edu