Alignment of beamlines
using x-ray beam
K. Klementiev, ALBA/CELLS
• is complement to mechanical alignment
• uses the optics components themselves + beam diagnostics
• is periodically done on every beamline
Outline:
• Introduction
• Available tools for beamline alignment
• Ray tracing of misaligned beamline (XAS)
• Entangled misalignments
• Alignment strategy
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Introduction
What others have done?
• There are a very few papers and web-pages on the topic
“Alignment of synchrotron beamlines”. Most of them are aimed at
automatic alignment.
• There is The Automatic Beamline Alignment Project
in ESRF (Olof Svensson et al). It is aimed at algorithms and software.
What I intend to present?
• not an automatic procedure, but rather basic understanding of misaligned
optics;
• to stress the importance of ray tracing for studying misalignments of
various kind;
• to notice the usefulness of the monochromator as a kind of diagnostics
device (never mentioned in literature, although some people use this);
• a (general) strategy for initial beamline alignment.
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Available tools for beamline alignment
z
3)
bent
toroid FM
side
low-E
filters
y
sample
5)
5)
DCM
piezo on
2nd crystal
bent CM
slit
MPW, 1m,
mask
period 80mm
1.5h×0.25v
K=13, B=1.74T
mrad2
Ec=10.4 keV
x
z
top
slit
2)
y
6)
1)
2)
3)
4)
5)
6)
7)
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1)
4)
1)
Z, X,
pitch,
yaw,
roll, R
FSM
1)
Bragg Z,
2 rolls
(miscuts)
FSM
FSM
5)
Z, pitch,
yaw,
roll, R
FSM
slit
x
1)
4)
7)
FSMs and/or BPMs
energy scan
rocking curve (piezo- or motor- actuated)
intensity monitors
slit scans
wave front analysis (pin-hole array)
secondary monochromator (x-ray emission spectrometer)
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Fluorescence screen monitors
screen view
roll df
pitch dq
height dz
tilt = df
Dx ~ 2L·dq·df
Dz ~ 2L·dq + 2dz
FSMs are of limited usage for initial alignment because:
• To detect image tilts due to a roll of ~1 mrad,
the screen resolution must be ~10 µm.
• In the initial alignment the screen itself has unknown Dx and Dz.
• Some misalignments give correlated shifts of the image,
e.g. pitch and height here.
• All the upstream optic elements contribute to the image.
Nevertheless, FSMs are useful for:
• localizing big misalignments,
• detecting relative shifts during energy changes,
• development of alignment strategy basing on the image shape,
• fine alignment basing on wave front analysis.
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Rocking curves
• Fine pitch scan of the 2nd crystal, ±0.01º (350 µrad): wide enough even at low energy 2.4 keV with
Si(111).
1) right after the monochromator,
• Two intensity monitors:
2) at the experiment.
a) to decouple intensity and position for the piezo-detuning feedback system;
Why two?
b) to detect the rocking curve shifts for alignment (see below).
If you have only one, you will only notice the asymmetry of the rocking curve, not the shift.
• Remember that the detuning of one of the crystals splits the energy band passed through the
monochromator. If you detune the 2nd crystal, one of the two sub-bands stays at the nominal
energy, the other is shifted proportionally to the detuning angle ( see also [Schulte-Schrepping & Drube,
NIMA 467–468 (2001) 396]). For the same intensity drop this shift is stronger at higher energies when
considered absolutely but stronger at lower energies when considered relative to the Darwin width,
i.e. it is more visible at lower energies.
Si 111, 2.4 keV
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Si 111, 9 keV
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Ray tracing of misaligned beamline (XAS)
• Click the buttons below to invoke the corresponding presentations.
• Ray tracing was done at 4 different energies (see the 4 columns)
• For each energy (column) there are two animated beam images:
1) behind the detuned optical element;
2) at the sample position.
All animations are synchronized, i.e. for the same detuning at a time.
• The rocking curves are recorded at the two positions:
a) after the DCM,
b) at the sample.
• The rocking curves are shown as
i. two 3D surfaces (for “a” and “b” rocking curves) in order to see if there
is a maximum over the detuning coordinate,
ii. as usual 2D plots (in the lowest row) to mimic the real measurements
of rocking curves; the “a” rocking curves are normalized to 1 and the
“b” rocking curves are normalized to ½.
Collimating
Mirror
(OpticalAlignment-1-CM.ppt)
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DCM
(OpticalAlignment-2-DCM.ppt)
Focusing
Mirror
(OpticalAlignment-3-FM.ppt)
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Ray tracing. Summary
Collimating Mirror
height
DCM
1st or 2nd
Xtal
height
low E
small hor. defocusing;
maximum → ~0.5 mm
similar
but ~no defocusing and
beam cut at small
Bragg angles (high E)
DCM
height no changes
except beam cut at small
Bragg angles (high E)
asymmetric vertical intensity
profile is not seen in the real
white beam!
pitch
low E
1st Xtal
roll
5
5
DX (mm) = 0.469
DZ (mm) = 3.438
DE (eV) = 0.188
DX (mm) = 0.313
DZ (mm) = 0.313
DE (eV) = 2.422
Intensity = 1360.62
Good rays = 11030
2399.7
Intensity = 16870.82
Good rays = 34884
2399.8
fixed
yaw
no defocusing;
weak max at high E → ~1 mrad
bending R
vert. defocusing;
no maximum;
E-analysis → ~10% R0
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high E
x 10
1.7999
2400
low E
hor. defocusing;
weak max → ~0.2 mrad
1.7998
Energy (eV)
0
Energy (eV)
Z (mm)
0
low E
~no defocusing;
maximum →
~0.5 mm
1st Xtal roll
-0.012
deg
4
roll
2399.9
Z (mm)
vert. defocusing;
no maximum;
image tilt → ~1 mrad
height
pitch
vert. defocusing;
no maximum (if within
1st Xtal roll
exit slit aperture);
-0.012 deg
Dx  tanq·df  energy dependent
low E:
high E:
hor. defocusing;
weak maximum →
~0.1 mrad
roll
Focusing Mirror
vert. defocusing;
no maximum;
image tilt → ~1 mrad
1.8
lateral
2400.1
1.8001
same
2400.2
1.8002
-5
-5
Xtal
miscuts
0
X (mm)
-5
5-5
2400.3
0
X (mm)
5
similar
hardly distinguishable
(next slide)
yaw vert. defocusing;
image tilt → ~1 mrad;
defocusing, no maximum;
similar to FM roll & lateral
bending R vert. defocusing;
no maximum;
defocusing
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Correlated misalignments
FM lateral =
±2 mm
FM roll =
FM yaw =
±25 mrad
±0.5 mrad
full beam 1.5h×0.25v mrad2
FM R =
½·R0 ..2·R0
R0=5.46 km
CM R =
½·R0 ..2·R0
R0=8.56 km
vertically reduced beam 1.5h×0.025v mrad2
horizontally reduced beam 0.15h×0.25v mrad2
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Alignment flow diagram 0
DX (mm) = 0.197
DZ (mm) = 0.040
DE (eV) = 0.763
align beamline
0.6
5999
5999.2
0.4
5999.4
5999.6
Energy (eV)
0.2
Z (mm)
set nominal CM pitch
set nominal DCM height and gap
set nominal FM pitch and height
set CM roll=0
set CM yaw=0
low heat load
Intensity = 138016
Good rays
N. rays = 592540
Intensity weight
0
-0.2
align CM height
+ FM height + FM pitch
(flow diagram 1)
6000
6000.2
6000.4
6000.6
-0.4
6000.8
-0.6
-0.6
-0.4
-0.2
0
X (mm)
0.2
0.4
6001
0.6
DX (mm) = 0.197
DZ (mm) = 0.088
DE (eV) = 0.756
align DCM rolls
and miscuts
(flow diagram 2)
Intensity = 121941
Good rays
N. rays = 601686
Intensity weight
high heat load:
750 W absorbed
by 1st Xtal
0.6
align DCM height
(flow diagram 3)
5999
5999.2
0.4
5999.4
5999.6
Energy (eV)
Z (mm)
0.2
align FM roll + FM lateral
+ FM yaw + CM R + FM R
(flow diagram 4)
5999.8
0
-0.2
5999.8
6000
6000.2
6000.4
6000.6
-0.4
6000.8
end
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-0.6
-0.6
-0.4
-0.2
0
X (mm)
0.2
0.4
0.6
6001
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Alignment flow diagram 1
align CM height
+ FM height + FM pitch
measure rocking curves
(RCs) at high E
align CM height by
looking for symmetric
RCs at low E
low E
high E:
symmetric
measure RCs at low E
align FM pitch by looking
for symmetric and not shifted
RCs at high E
what
do the RCs look
like?
high E: symmetric
low E: symmetric and shifted
low E
high E
high and low E:
symmetric and not shifted
align FM height by looking
for intensity maximum
end
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Alignment flow diagram 2
align DCM rolls
(miscuts)
take “beam image”
at the sample at high E
go to low E.
Important! Use calibration curve
“roll vs. 2nd Xtal translation”
do 2D scan roll1 roll2 by
looking for maximum intensity
take “beam image”
at the sample at low E
reduce the vertical exit slit
down to the high E image
size
1st Xtal roll
low E
1.7998
high E
2399.8
1.7999
0
Energy (eV)
Z (mm)
Z (mm)
2399.9
0
1s
Intensity = 16870.82
Good rays = 34884
Intensity = 1360.62
-0.012 deg
Good rays = 11030
5
2399.7
5
what
do the images look
like?
DX (mm) = 0.313
DZ (mm) = 0.313
DE (eV) = 2.422
DX (mm) = 0.469
DZ (mm) = 3.438
DE (eV) = 0.188
Energy (eV)
Dx = 2L·tanq·df.
E.g. if you have 30 µrad
roll change when you
translate the 2nd Xtal
and L=15m:
Dx~1mm.
2400
2400.1
1.8
1.8001
2400.2
1.8002
high and low E:
same horizontal position
-5
-5
0
X (mm)
-5
5-5
2400.3
0
X (mm)
5
end
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Alignment flow diagram 3
align DCM height
go to high E
(small Bragg angles)
scan DCM height to find the two positions
when the footprint is out of the Xtal surface
(seen as decrease of intensity);
take the middle of the two
end
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Alignment flow diagram 4
align FM roll + FM lateral
+ FM yaw + CM R + FM R
set FM roll=0
take “beam image_full”
at the sample at arb. E
with widely open exit slit
reduce vertical exit slit
and take “beam image_hor”
optimize
CM R and FM R
by doing 2D scan and
looking for max intensity
make horizontal beam
open vertical exit slit
reduce horizontal exit slit
and take “beam image_vert”
which beam shape gives
the stronger beam size
reduction in vertical?
optimize
FM lateral1+ FM lateral2
by doing 2D scan and
looking for max intensity
make horizontal beam
no reduction
end
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Q&A
What are the generalities for all beamlines ?
• Rocking curves are asymmetric under motion of mirrors and crystal into/out of the
beam. E.g. if you have an intensity monitor upstream your KB system, you can easily
decouple at least 2 of the N (=7? 8?) degrees of freedom.
• Miscut and roll misalignment in crystals lead to energy-dependent horizontal shifts.
This presentation is about a hard x-ray beamline. What would differ for a soft one?
• Don’t know.
How to repeat the ray tracing for another beamline?
• The Matlab scripts are freely available. Prepare Shadow projects for different energies
in the way that the OE positions are fixed and coincide with the physical ones. Ask me
for further help.
Outlook
• Ray tracing with the pinhole array at defocusing/de-collimating conditions and
thermal bumps.
• Programs for pinhole image analysis + inverse problem. May I have a student for this?
• Eventually, automatic beamline alignment based on the pinhole images.
Thanks
• to J.Nicolás for introduction into the analysis of the imaging properties by means of the
path function. Using his approach (ask him for the article) and the tools like Mathematica
one can analyze the images without ray tracing. I don’t know what is easier though.
19.09.2008
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