The secondary source of
NANOSCOPIUM
A new system of slits, designed at SOLEIL,
is deployed on the NANOSCOPIUM beamline
to define a second, more stable light
point source, with better resolution. The
very high precision required of these slits
(<0.5 µm on the position, <0.1µm on the
mechanical resolution) makes it a real
challenge to design them, from the design/
manufacture standpoint. In addition, their
tremendous stability will allow Zone Plate
and Kirkpatrick-Baez optical focusing
configurations to be used for experiments
with a spatial resolution of 30 nm. This set
of (horizontal and vertical) slits is located
in a vacuum of the order of 10
-9
mbar.
The NANOSCOPIUM beamline is one of the
long beamlines at SOLEIL. This multi-mode
beamline will be used in the 5-20 keV
energy range, and dedicated to scanning
x-ray micro- and nano-probe experiments
with a spatial resolution of 30 nm to 1 µm.
Both mirrors M1 and M2 of the
NANOSCOPIUM beamline have a fixed
curvature and focus on a system of
slits that defines a secondary source.
This system is located 85 m from the
main source, which is a U20 in-vacuum
undulator. This beamline currently operates
with a double-crystal monochromator. By
2016, it could also operate with another,
multilayer-type monochromator, which will
provide up to 5 W power according to the
energy range chosen. The power currently
received by this secondary source is less
than a milliwatt. To prepare for this future
monochromator, we have decided to cool
the secondary source with water, via
copper braids.
These slits have positioning precision of
<
0.5 µm
with actuator resolution <
0.1µm.
The opening value in operating mode
is
5 to 50 µm.
The maximum vertical
positioning travel to align the slit on the
incident beam is
±3 mm.
The maximum
horizontal travel is
30 mm.
This movement
also allows for a ‘clearance’ position, which
allows the direct beam to pass through
with a 20 mm horizontal and 6 mm vertical
opening. The opening of the two horizontal
slits is
2 mm.
The focal plane of mirrors M1 and M2 is
located
at the secondary source with
a beam size of 1.5 × 0.066 mm² (H×V)
FWHM and divergence of 0.03×0.02
mrad (H×V) FWHM.
The secondary source assembly can
translate manually along the axis of the
beam for the purpose of adjustment of the
order of ±500 mm.
This adjustment is necessary for the
alignment of the slits and to compensate
for defects in mirrors M1 and M2 located
upstream along the beamline.
This assembly must be perfectly stable,
with the slits having an eigenmode
greater than 60 Hz and the stand having
an eigenmode greater than 100 Hz. The
maximum vertical variation is less than
100 nm.
This secondary source is located in an
air-conditioned room whose temperature
is regulated to within ±0.2°C.
This assembly is securely attached
to a flange with alignment reference.
The flange is mounted on three feet to
allow the various tests on a bench in the
laboratory, with offset acquisitions between
the two slits and an alignment reference
securely attached to the flange.
The linear actuator operates in-vacuum
and consists of a stepper gearmotor that
provides 24 mm travel in translation. It
translates a wedge, which is guided with
respect to the fixed platform by a ball rail.
This wedge is symmetrical to allow
symmetrical action with respect to the slit.
An arm guided by the wedge via another
ball rail actuates a sine bar arm. This
means that a translation of the wedge
actuates the sine bar arm with respect
to an axis securely attached to the fixed
platform.
This sine bar arm pushes against one
of the two knife-edges of the slit. This
knife-edge translates along its guide,
a deformable parallelogram, whose base
is securely attached to the fixed platform.
The main advantage of this set-up is
that the mechanical errors introduced by
the various guide elements are reduced,
thanks to the gear reduction ratio of the
sine bar arms, which takes place only via
flexible elements without play or friction.
MODELING, METHODOLOGY AND INSTRUMENTATION
128
SOLEIL
HIGHLIGHTS
2013
