Cryogenic payloads and cooling systems
(towards a third generation interferometer)
part I: An Interferometer at
Cryogenic Temperatures
Piero Rapagnani
I.N.F.N. Sezione di Roma
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Why cool the mirrors?
Test masses and suspensions thermal noise reduces at low temperature:
< x 2 T
Thermoelastic noise both of the mirror substrates and coatings decrease:
< x 2  aT

2
Thermal expansion rate a decreases at low temperature;
Mechanical Q of some materials increases at low temperature
@ w << w
int
T
2
< x 
Thermal lensing:
Q
Thermal conductivity increases and consequently reduces thermal


gradients on the coating;
Refraction index variation with temperature is very small at low
temperature;
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
R&D on Cryogenics
1) Study of the refrigeration system
- noise
- refrigeration power
2) Suspension compatibility: thermal
conduction and acoustic quality factor Q
measurements
3) Sensors at low temperatures
- accelerometers and position sensing devices
- actuators
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Liquid helium
Refrigerators
Hybrid system
Issues to cool the mirrors

Refrigeration system:
•
The injected mechanical noise must be negligible, the
sensitivity must be preserved:
 Good mechanical isolation between the mirror
and the cooling system;
•
Cooling time of the mirror as low as possible:
 Good thermal couplings;

 High refrigeration power;
Suspension system compatible with good mechanical and thermal
couplings:
•
•
Thermal conductivities change with temperature;
Mechanical quality factor Q;
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Cryogenic fluids and G.W. Detectors
The first cryogenic antenna in the world 1974-1980:
M=20 kg, T =4 K , n ~ 5 kHz
No excess noise
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
The second cryogenic antenna of the Rome group -1978:
M~ 400 kg, T =4 K , n ~ 1.8 kHz
Excess noise in the first
phase of operation:
Due to suspension system!!
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Advantage of the
superfluid liquid
Helium:
the  transition
He phase transition to superfluid
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Data from the
Antenna
EXPLORER
installed at
CERN
• The current technique to
cool down a Resonant Antenna
requires “Heavy Work” and
several weeks
• Detector duty cycle: less
than 1 month.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
• For an interferometric
antenna 6 masses to be
cooled.
• To preserve the duty
cycle this “heavy work”
must be done in
parallel.....
VIRGO
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
In a BIG Laboratory,
large Cryogenic Facilities are possible
The example of LHC at CERN:
The Cryogenic Distribution
Line (QRL) for the LHC
(Large Hadron Collider).
Each of the eight ~3.2 km
QRL sectors is feeding
Helium at different
temperatures and pressures to
the local cooling loops of the
strings of superconducting
magnets operating in
superfluid helium below 2 K.
With an overall length of 25.8
km the QRL has a very
critical cost to performance
ratio.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Technologies are available, but are VERY expensive and
require extensive manpower
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
An alternative way to cool down without liquid helium:
the new generation of Cryocoolers
• A Pulse Tube Refrigerator
(PTR) or "G-M style" pulse
tube cryocooler, is a
variant of a GiffordMcMahon (GM) cryocooler.
First stage
• PTR operate at low
frequencies, typically <5
Hz.
• Used a conventional oilflooded G-M compressor and
a valve set near the cold
head to convert the
continuous flow of helium
to a low frequency
pressure wave.
Piero Rapagnani – INFN Roma
ILIAS
Second stage
Suitable for applications that require efficient
operation:
No moving parts in cold head. Minimal
vibration, low acoustic noise, reliability.
High efficiency: 2 to 3 times higher
efficiency than GM cryocoolers for loads
temperatures between 55 and 120 K.
April 27th, 2006
A possible solution
Passive vibrational
isolation system for
the heat link
 Long heat link
 Part of the
refrigerating power
absorbed by the
isolators
 Attenuation of the
refrigerating power
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Our solution
Active vibration
isolation system
for the heat link


Shorter heat link
Refrigerating
power preserved
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Q from refrigerator
Vacuum Chamber
and Cryostat
Thermal Shields
Marionetta Reaction Mass:
Thermal Shield at ~ 4K
High Efficiency Thermal Links
Silicon Monolithic Wire
Mirror Reaction Mass:
Thermal Shield at ~ 4K
Q from laser beam
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Q from refrigerator
Vacuum Chamber
and Cryostat
Thermal Shields
Marionetta Reaction Mass:
Thermal Shield at ~ 4K
High Efficiency Thermal Links
Silicon Monolithic Wire
Mirror Reaction Mass:
Thermal Shield at ~ 4K
Q from laser beam
Rough Estimates give
Tmirror ~ 10 K
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Q from Superfluid Helium Reservoir
A hybrid system using
Superfluid Helium could
allow to reach T ~ 1.5 K
Vacuum Chamber
and Cryostat
Thermal Shields
Marionetta Reaction Mass:
Thermal Shield at ~ 1.5 K
High Efficiency Thermal Links
Silicon Monolithic Wire
Mirror Reaction Mass:
Thermal Shield at ~ 1.5 K
Q from laser beam
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
Thermal Links:
Many Materials and
Composites available
Thermal behavior
at low temperatures
must be tested
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006
The short/medium term future:
The Cryogenic Suspension Test
Facility
Still non investigated Problems:
Piezo
Actuator
Piezo
Actuator
Cryogenic (T~ 50 K)
Suspension Elements
Thermal link (T ~ 4 K)
Piero Rapagnani – INFN Roma
ILIAS
April 27th, 2006