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Journal ArticleDOI

A cryogenic payload for the 3rd generation of gravitational wave interferometers

01 Sep 2011-Astroparticle Physics (North-Holland)-Vol. 35, Iss: 2, pp 67-75

Abstract: Thermal noise is a limiting factor of interferometric gravitational wave detectors sensitivity in the low and intermediate frequency range. A concrete possibility for beating this limit, is represented by the development of a cryogenic last stage suspension to be integrated within a complex seismic isolation system. To this purpose a last stage payload prototype has been designed and built. It has been suspended within a dedicated cryostat with the same technique adopted for the VIRGO payload and making use of two thin wires in a cradle configuration to support a mirror made of silicon. The cooling strategy, the thermal behaviour and the system mechanical response have been deeply studied while a measurement characterization campaign has been performed both at room temperature and at cryogenic temperature. In this paper, the preliminary results obtained together with the first cooling down of the 300 kg overall mass payload at about 25 K, are reported. This study will play a driving role in the design of the third generation gravitational wave detector.
Topics: Payload (57%), Gravitational-wave observatory (56%), Cryostat (55%), Cryogenics (53%), Gravitational wave (51%)

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A cryogenic payload for the 3rd generation of
gravitational wave interferometers
F. Basti, F. Frasconi, E. Majorana, L. Naticchioni, M. Perciballi, P. Puppo, P.
Rapagnani, F. Ricci
To cite this version:
F. Basti, F. Frasconi, E. Majorana, L. Naticchioni, M. Perciballi, et al.. A cryogenic payload for the
3rd generation of gravitational wave interferometers. Astroparticle Physics, Elsevier, 2011, 35 (2),
pp.67. �10.1016/j.astropartphys.2011.05.004�. �hal-00782943�

Accepted Manuscript
A cryogenic payload for the 3rd generation of gravitational wave interferometers
F. Basti, F. Frasconi, E. Majorana, L. Naticchioni, M. Perciballi, P. Puppo, P.
Rapagnani, F. Ricci
PII: S0927-6505(11)00088-0
DOI: 10.1016/j.astropartphys.2011.05.004
Reference: ASTPHY 1596
To appear in: Astroparticle Physics
Received Date: 17 January 2011
Revised Date: 9 May 2011
Accepted Date: 12 May 2011
Please cite this article as: F. Basti, F. Frasconi, E. Majorana, L. Naticchioni, M. Perciballi, P. Puppo, P. Rapagnani,
F. Ricci, A cryogenic payload for the 3rd generation of gravitational wave interferometers, Astroparticle Physics
(2011), doi: 10.1016/j.astropartphys.2011.05.004
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
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Submmitted to Astroparticle Physics
A cryogenic payload for the 3rd generation of gravitational wave interferometers.
F. Basti
1
, F. Frasconi
3
, E. Majorana
2
, L.Naticchioni
1,2
,
M. Perciballi
2
, P. Puppo
2
, P. Rapagnani
1,2
, F. Ricci
1,21
1
Department of Physics, University of Rome La Sapienza
2
I.N.F.N. Sezione di Roma , 00185 Roma, Italy
3
I.N.F.N. Sezione di Pisa, 56127 Pisa, Italy
Abstract
Thermal noise is a limiting factor of interferometric Gravitational Wave de-
tectors sensitivity in the low and intermediate frequency range. A concrete
possibility for beating this limit, is represented by the development of a cryo-
genic last stage suspension to be integrated within a complex seismic isolation
system. To this purpose a last stage payload prototype has been designed and
built. It has been suspended within a dedicated cryostat with the same tech-
nique adopted for the VIRGO payload and making use of two thin wires in a
cradle configuration to support a mirror made of silicon.
The cooling strategy, the thermal behaviour and the system mechanical re-
sponse have been deeply studied while a measurement characterization cam-
paign has been performed both at room temperature and at cryogenic temper-
ature. In this paper, the preliminary results obtained together with the first
cooling down of the 300 kg overal mass payload at about 25 K, are reported.
This study will play a driving role in the design of the third generation Gravi-
tational Wave detector.
Keywords: Cryogenics; Gravitational wave detectors.
1 Introduction
Low temperature physics and Gravitational Wave (GW) search met each other
several years ago when W. Fairbank proposed the development of a resonant
GW antenna cooled in the mK range [1]. The first detector weighting 20 kg was
successfully cooled down to 4 K by the group headed by Edoardo Amaldi and
Guido Pizzella in 1974 [2]. The cooling runs were very useful to acquire expe-
rience in the cryogenic techniques and to understand the mechanical elements
1
Corresponding author: Fulvio Ricci, Department of Physics, University of Rome La
Sapienza, Piazzale A. Moro 2 , I-00185 Roma, Italy. E-mail: fulvio.ricci@roma1.infn.it
1

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behavior as well as their material properties in the low temperatures range. A
second important result was reached when three similar detectors were operated
in coincidence, at CERN (Geneva), Stanford and Baton Rouge collecting data,
for the first time, at liquid helium temperature. [3]. These milestones marked the
starting point of the Gravitation Wave search era based on resonant antennae
operated at cryogenic temperature and having a narrow detection bandwidth.
The current GW antennae are broadband detectors based on the working
principle of a Michelson interferometer. They have been designed for the first
direct detection and together with their advanced versions, presently in the
preparation phase, are operated at room temperature looking at typical GW
sources distant up to 100 Mpc [4], [5]. However, for an effective GW astronomy
the antenna sensitivity should be increased ten-fold requesting an additional
effort for the study of third generation interferometers which has just started
[6]. One of the dominant noise sources limiting the present interferometers
sensitivity is the thermal noise of the suspended optics. This limit can be
overcome by cooling the suspended mirror at cryogenic temperature [7].
Many noise sources have a direct dependence on temperature while others
are linked to it through the material properties. The brownian forces, for in-
stance, drive the fluctuations of the mirror internal modes and those ones of its
suspension wires. These phenomena are well quantified through the Fluctuation-
Dissipation theorem, putting in relationship the system dissipation to the dis-
placement noise power spectrum. On the other hand, great importance is due
to dissipation mechanisms directly related to the temperature fluctuations, like
the thermoelastic effect measurable in the wire suspension as well as in the mir-
ror substrate and coating. This contribution depends on the materials elastic
expansion coefficient and it is proportional to the second power of temperature.
The use of cryogenic techniques in the development of future GW detectors
is also connected to the reduction of the thermal lensing due to the temperature
gradients within the mirror substrate and coating. This effect is linked to the
thermal conductivities and to the fluctuations of the coating refraction index.
Since the thermal expansion coefficient decreases at low temperature reducing
drastically the mirror deformation induced by the high light power stored in the
optical cavities of the interferometer, the cryogenic approach seems to be the
natural one.
For an effective use of low temperature technique in a GW detector, the
design of a last stage suspension has to change in accordance with a couple of
new guide lines:
- the transmission of the refrigeration power to the mirror level should not
deteriorate the position control performance;
- the residual vibration transmitted to the mirror through the cooling sys-
tem, should be well below the detector noise sensitivity curve.
With these requirements it is extremely important to have a good mechanical
2

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isolation between the mirror and the cooler. Moreover the importance of a good
thermal link between the payload and the cooling system has a fundamental role
in the design optimization, taking care of having links as short as possible and
good thermal couplings, so to avoid refrigeration power losses. The use of a
mechanical attenuation system as a heat link, is a good solution to filter the
vibrations of the cryo-cooler, with the drawback to limit the heat flow. On
the other hand the mirror suspension itself must have the required thermal
conductivity reducing thermal gradients and optimizing the cooling time.
According with the guide lines described above, the overall design of the
mirror suspension and its control system will be very different from those ones
presently used in interferometric antennae. The new system will be the result of
a trade off between the need to have a strong thermal contact with the cooling
system and the tentative to reduce any dissipation source due to the coupling
of the suspension with the mirror.
In the following sections we present the first attempt to design a cryogenic
payload studying both the mechanical and thermal issues via finite element
analysis. Then, we describe the first prototype, that has been built and cooled
at low temperature. In the last section we report and discuss the experimental
results aimed to the prototype characterization.
2 The payload mechanical design.
The most relevant peculiarity of the VIRGO interferometer for gravitational
waves detection is represented by the use of a seismic noise isolation system,
the Superattenuator (SA), developed to extend the detection bandwidth in the
low frequency region starting from a few Hz. Conceptually, it is based on a
cascade of several mechanical passive filters forming a long pendulum chain,
attached to the top of a three legs structure conceived on the working principle
of an Inverted Pendulum [8]. The seismic noise passive filtering performance
of the mechanical structure is completed with an active filtering action in the
low frequency region (below 5 Hz where the inner modes of the structure are
confined) obtained with a few sets of sensors-actuators disseminated along the
multi-stage suspension system. The basic idea is that the faster the position
corrections are needed to keep in operation the detector, the closer to the mirror
they must be applied. In this context, the role of the last stage payload is
crucial. By using the actuators of the last stage, it must be possible to perform
the alignment in DC of the test masses, to compensate the residual seismic
noise below 2 Hz and to steer the optical components maintaining the relative
position of the interferometer mirrors. The last stage suspension is essentially
a double-stage branched system with the so-called marionette as first element
chain. The reaction mass and the mirror, both suspended from it, representing
the second branch. The idea of using a reaction mass to control a suspended
mirror has been originally studied by the GEO group in great detail. [10] The
3

Citations
More filters

Journal ArticleDOI
Abstract: Many studies worldwide are currently developing interferometric methods for detecting gravitational waves and one of the challenges in such methods has been to sufficiently cool the mirror in interferometric detectors in order to reduce thermal noise. Although the mirror is surrounded by a radiation shield, a hole in the shield is necessary to allow the laser beam to pass. To reduce the thermal radiation caused by the presence of the hole, we will install a duct shield with baffles. To calculate the heat input through the duct shield, we applied a ray trace model whose results were consistent with those of an experiment without baffles. As an application of our model, the heat input in the case of KAGRA (a Japanese cryogenic gravitational wave detector project) was calculated. Our analysis suggests that baffles in the duct shield can considerably reduce the heat input in KAGRA.

9 citations


Dissertation
01 Jan 2012
Abstract: Albert Einstein in 1916 predicted the existence of a Gravitational Wave in his General Theory of Relativity. These waves, which propagate at the speed of light transmit gravitational information through the Universe. Since its prediction by Einstein, astronomers and physicists have searched for them and developed method to detect them. Though so far unsuccessful, the search of Gravitational waves goes on and great efforts are being made to develop the most sensitive detectors yet in the hope of that first detection. Currently ground based detectors are limited by coating Brownian thermal noise due to excitation of the reflective coatings applied to the test masses. Through measurement of mechanical loss of a material the magnitude of the Brownian thermal noise can be determined. It is necessary to determine the root cause of mechanical loss in current coatings (Ta2O5¬ and SiO2). Work towards this goal is taking place on multi paths, directly, through characterisation of mechanical loss and indirectly through microscopy studies to determine the structural cause. In this thesis, the effect of TiO2 doping and heat treatment of Ta2O5 has been investigated. It has been previously shown that a TiO2 doping of Ta2O5 reduces the mechanical loss and that, that reduction is at a maximum at 30% TiO2. It has been determined through Electron Diffraction experiments that the structure of TiO2 doped Ta2O5 becomes more homogenous up to 30% doping. Through computation modelling of these structures using Density Functional Theory it has also been determined that the abundance of TiTaO2 ring formations also maximises at 30% doping. Further modelling has also determined that the TiTaO2 rings are more flexible that their counter parts of Ta2O2 and Ti2O2. From this it has been hypothesised that the overall flexibility of a structure is a strong component of the mechanical response of the structure. Hence by increasing the flexibility through TiO2 doping the mechanical loss (as Thermal Noise) is decreased similarly and this response would also be expected using similarly flexibility improving dopants.

7 citations


Cites background from "A cryogenic payload for the 3rd gen..."

  • ...aLIGO will be operated at room temperature however cooling remains an option for future detectors/upgrades [29, 53] Lowering the temperature poses certain problems; firstly it is expensive to pump liquid nitrogen or helium around the mirrors to cool them....

    [...]


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