Transcript Slide 1 - Nikhef

RasClic: A long-baseline 3-point alignment system for Linear Accelerators
H. Manaud Durand, J-P. Quesnel, T. Touzé
CERN TS-SU, Geneva, Switzerland
Harry van der Graaf, Henk Groenstege, Elmar Reinhold, Geert Hanraads
Nikhef, Amsterdam, The Netherlands
Mark Beker, Marc Kea, Hidde Westra
Nikhef/Delft University of Technology, The Netherlands
laser +
beam expander
diffraction
plate
Rogier van der Geer
Nikhef/University of Leiden, The Netherlands
pixel image
sensor
Taylan Tozgorto
University of Amsterdam, The Netherlands
contact: [email protected]
RasClic is a new optical alignment system for large objects like linear accelerators,
based on the RASNIK alignment system*. The system is a 3-point straightness monitor
consisting of a monochromatic light source, a diffraction plate and a pixel image
sensor. By monitoring the position of a diffraction pattern on the image sensor, a
measure for the relative positions of the three components is obtained. It has been
shown that such a system can meet the required alignment tolerances for use as an
alignment system for the Compact Linear Collider (CLIC).
* [1] H. Dekker, H. van der Graaf, H. Groenstege, F. Linde, S. Sman, R. Steensma, B. Jongkind, A. Smeulders: The RASNIK/CCD
3-Dimensional Alignment System Proceedings of the 3rd International Workshop on Accelerator Alignment, (IWAA 1993), 28 Sept
- 1 Oct 1993, Annecy, France
f x sx ,y sy F ω
x
,ω
i ω
y
e
s ω
xx
s
yy
The RasClic vacuum tube in the TT1 tunnel at CERN.
Recently the length increased from 91 to 140 m.
Laser fiber-optic coupling system,
eliminating drift in laser beam position
Typical diffraction
pattern seen by
pixel image sensor
(Allied Vision
Technologies
Pike F100B,
500 x 500 pixels,
pitch 7.4 μm.)
A position resolution
of 20 nm is reached
Diffraction plate: transparant
ring with inner/outer diameter
of 80/100 mm
Noise spectrum
Linearity tests were performed by varying a force on
the diffraction plate holder of up to 50 N in the vertical
direction. These tests show an excellent position
resolution and linearity.
λ
RasClic as a Seismograph
The results of the noise- and sensitivity studies show that
RasClic could be used as a low-frequency seismograph
to monitor the 'earth hum'.
There is evidence that the 1/f noise is to a large part due to
temperature fluctuations; a system of T sensors is set up to
eliminate this noise contribution. Further work needs to be
done on the resolution.
The main practical limitation
for increased sensitivity at low
frequency by extending
RasClic to an ideal 20 km is
the need for a long vacuum
tube.
The relatively cheap laser,
diffraction plate and pixel
sensor can work in principle at
any distance, provided they
are well coupled to the earth's
crust individually.
An interesting application of
RasClic is as an instrument to
monitor the slow deformation
of the earth's crust across a
fault line.
Noise behavior of an ideal RasClic compared to the STS-1 and STS-2
seismographs used by the Royal Dutch Institute for Meteorology (KNMI)
[13]. The NHNM and NLNM envelopes are the
New High- and New Low Noise Models, respectively. These are models for
the background noise in seismic measurements due to actual movements in the
Earth's crust, during periods of high and low seismic activity, respectively.