Installation
at CAMD
and operation of the LNLS double-crystal
monochromator
Paul J. Schilling and Eizi Morikawa
The .I. Bennett Johnston, Sr. Center for Advanced Microstructures and Devices, Louisiana State University,
Baton Rouge, Louisiana 70803
H&o Tolentino and Edilson Tamura
Laboradrio
National
de Luz Sincrotron, LNLSJCNP4, Campinas, 13081, Brazil
Richard L. Kurtz
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803
Cesar Cusatis
Department0 de Fisica, Umiversidade Federal do Paranli, Curitiba, 81531, Brazil
(Presented on 21 July 1994)
Anew x-ray beamline has been installed at CAMD utilizing a two-crystal monochromator designed
and built at LNLS. The beamline will operate in the 2-18 keV range using up to 4 mrad of dipole
radiation from the CAMD storage ring. The monochromator maintains a fixed exit beam and fixed
positions of the beam on the two crystals using mutually perpendicular elastic translations. With the
ring operating at 1.5 GeV and 160 mA, Si(220) crystals will provide a flux of -3(109) photons/s/
mrad at 8 keV, with an energy resolution AE <2 eV, to the experimental hutch. The beamline is
equipped with an EXAFS endstation and will also be used for other x-ray applications at CAMD.
First results are presented. 0 1995 American Institute of Physics.
1. INTRODUCTION
Collaborative efforts between the Center for Advanced
Microstructures and Devices (CAMD) at Louisiana State
University, and the Laboratbrio National de Luz Sincrotron
(LNLS) at Campinas, Brazil, have resulted in the installation
and operation of a joint LNLS/CAMD x-ray beamline at the
CAMD facility. The beamline utilizes a two-crystal monochromator designed and built at LNLS,l and will operate in
the 2-18 keV range using up to 4 mrad of dipole radiation
from the CAMD storage ring. The beamline is supported
jointly by the State of Louisiana and the government of Brazil through CAMD and LNLS.
The CAMD storage ring is optimized for the production
of soft x rays and was designed to operate in the range of
1.2-1.4 GeV with respective beam currents of 400 and 200
mA.’ The performance, however, exceeds the specifications,
easily attaining an electron-beam energy of 1.5 GeV.3 This
increases the critical photon energy to 2.6 keV and makes x
rays with energies in excess of 10 keV available from bending magnet radiation. Figure 1 presents the photon flux theoretically evaluated at 1.2 and 1.5 GeV and the maximum
currents currently attainable for the energies.
fining slits before and after the monochromator, located 9.2
and 11.8 m from the source, allow manual adjustments of the
horizontal acceptance from 0 to 50 mm and automated control of the vertical opening from 0 to 10 mm. The first crystal
of the monochromator is located 10.6 m from the source
point.
The LNLS fixed exit double-crystal monochromator utilizes one rotation and mutually perpendicular translations of
the crystals in a Golovchenko configuration,4 with stepping
motor controlled elastic translations maintaining the geometry. Detuning or fine angular adjustments for parallelism are
performed using a solenoid/magnet device.’ The mechanism
allows an 8”-60” range of motion. Up to three pair of crystals can be mounted simultaneously. Currently Si(ll1) and
Si(220) crystals are mounted, and the beamline is operated
over photon energies from 2.3 to 18 keV. These crystals are
II. BEAMLINE LAYOUT
The beamline layout is presented in Fig. 2. A 125 ,um
beryllium window separates the UHV system from the
monochromator, which is operated at -10e4 Torr. The UHV
system includes a fast closing shutter (<lo ms from signal to
close) and an acoustic delay line, 1.8 m in length, consisting
of 11 baffle plates with effective D/d ratio of about 4. The
monochromator vacuum section extends through the wall of
the experimental hutch and ends with a 50 ,um kapton window. The maximum horizontal acceptance is 4.3 mrad. De2214
Rev. Sci. Instrum.
66 (2), February
1995
Photon energy (eV)
FIG. 1. Synchrotron-radiation liux output from CAIvlD bending magnets.
0034-6748/95/66(2)/2214/3/$6.00
0 1995 American
Institute
of Physics
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I
,
1
I
I
I
FIG. 2. LNLS/CAMD
I
I
I
1
1
I
I
double-crystal monochromator beamline layout.
each approximately 2 cmX2 cm, which limits the acceptance
angle to about 2 mrad. The vacuum chamber is mounted on
a table which allows translation’orthogonal to the beam di,
rection in order to change crystals. 33 cm long bellows connecting both sides of the monochromator allow this translation to be made without disturbing the monochromator
vacuum system.
The beamline ends in a large (3 mX6 m) experimental
hutch equipped with an EXAFS workstation. In addition,
x-ray images can be acquired using a commercial phosphor
image-plate system? Images are obtained by scanning test
objects through the beam on an x-y translation stage, along
with an 8 in.XlO in. image plate.
photons/s/mrad/mA. The optimum operating conditions for
the storage ring are 290 mA at 1.3 GeV and 160 mA at 1.5
GeV.
Ray tracing calculations for the beamline were performed using SHADOW.~The source was generated using parameters for the CAMD ring operating at 1.3 and 1.5 GeV,
and ray tracing was performed to simulate the optical system
with the entrance slit set as in the above measurements. The
calculated values for flux entering the hutch are presented in
Figs. 3 and 4 for comparison to the measured values.
The energy resolution canbe calculated from the differential form of the Bragg equation
Ill. FLUX AND ENERGY RESOLUTION
where A.8 is determined by the angular spread of the iricident beam (48,,)
and the intrinsic reflection width of the
monochromator (A0=).
The FWHM energy resolution
AEIE can be approximated using a quadratic summation to
give’
Flux measurements were performed using a silicon p-n
junction photodiode.” The diode is expected to have 100%
internal quantum efficiency up to 6 keV. The efficiency will
decrease at higher photon energies due to the limited silicon
thickness (30 prn)i7 The entrance slit was set at a. vertical
opening of 0.6 mm for the measurements. Harmonic contamination was observed in rocking curves collected below 6
keV, necessitating detuning for harmonic rejection. Measured
values of flux exiting the kapton window using Si(ll1) and
Si(220) crystals during ring operation at 1.3 and 1.5 GeV are
reported in Figs. 3 and 4. These values are reported in
AEIE
= AX/h = A@ cot Os,
AWX=AE/E=(A~;~+AC~;)~‘~
cot eB.
From the SHADOW simulations described above, 40 for the
beam after the entrance slit was calculated to be 0.061 mrad.
Using this value for A8,, and the double-crystal rocking
curve widths for he,,
values of AE corresponding to the
intensity data in Figs. 3 and 4 were calculated, and appear in
‘OS-
-
SHADOW
Measured
SHADOW
Measured
___--
results
values
results
values
for
for
for
for
1.5
1.5
1.3
1.3
GeV
GeV
GeV
GeV
+
,04 r
x
,
5000
Energy
10000
103
20000
(eV)
Vol. 66, No. 2, February
1995
crystals with 0.6
-.
x
1
10000
5000
Energy
FIG. 3. Flux entering experimental hutch using Si(ll1)
mm vertical opening at entrance slit.
Rev. Sci. Instrum.,
-----
SHADOW results for 1.5 GeV
Measured values for 1.5 GeV
SHADOWresultsfor1.3GeV
Measured values for 1.3 GeV
j
20000
(eV)
FIG. 4. Flux entering experiment hutch using Si(220) crystals with 0.6 mm
vertical opening at entrance slit.
Synchrotron
radiation
2215
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FIG. 8. Image of a test object obtained with 9.5 eV photons. The sample
contains water, air, and calcium phosphate.
EnergyWI
FIG. 5. Calculated energy resolution with 0.6 m m vertical opening at entrance slit.
Fig. 5. Obviously, either flux or energy resolution can be
improved (at the expense of the other) by adjusting the slits.
Thus as an example, using the Si(220) crystals at 8 keV,
operating at optimum current for 1.5 GeV, the Aux entering
the hutch will be -3(109) photons/s/mrad, with energy resolution AE-1.2
eV, AEIE- 1.5(10m4).
IV. FIRST RESULTS
Energy
(eV)
FIG. 6. XANES spectrum at the K edge of Cu (8979 eV).
I-
I.,
.
1.
I..
I,.
------A
,
9000
.,
,
I
,
,
,
9200
,
,
,
,
9400
Energy
,
9600
(eV)
FIG. 7. EXAFS spectrum at the K edge of Cu(8979 eV).
2216
Rev. Sci. Instrum.,
Vol. 66, No. 2, February
1995
Absorption measurements were performed on 9 pm
thick Cu foil using Si(220) crystals with the entrance slit set
at a 0.6 mm vertical opening, as in the above flux measurements. XANFB and EXAFS spectra at the K edge of Cu
(8979 ev) appear in Figs. 6 and 7. The sharp feature on the
absorption edge indicates that the resolution is better than 2
eV, which is consistent with the calculated value reported
above.
Experiments have also been performed using the imageplate system. In Fig. 8, a transmission image of a test object
obtained at 9.5 keV is presented. The test object consists of a
box constructed of 3 mm thick Plexiglas tilled with 1 cm of
paraffin wax. Imbedded in the paraffin are water droplets, air
bubbles, and calcium phosphate. The larger oval features are
water droplets and the smaller black regions are air bubbles
which are often found within the water droplets. The smallest
light features are calcium phosphate particles of varying
sizes. The particle indicated by the arrow, located near a
water droplet, is roughly 100 m across by 300 ,um wide.
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Synchrotron
radiation
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