Transcript C1 (Ricci)

G.W. Interferometers
&
Cryogenics
ILIAS -STREGA: task C1
Fulvio Ricci
Dipartimento di Fisica, Università di Roma La Sapienza
&
I.N.F.N. Sezione di Roma
Fulvio Ricci
ILIAS
Novenber, 02 2004
Cooling mirrors: the task C1
Cryogenic Payload Design
Cooling configuration study:
-experimental test
-computer simulation
Refrigeration system study:
The cryogenic facility:
- Vibration Free Cryostat (V.F.C.)
Cryogenic Instrumentation for the monitor and control
low frequency accelerometer
high frequency accelerometer
displacement sensor
Fulvio Ricci
ILIAS
Novenber, 02 2004
Cryogenic Payload Design
Cooling configuration study:
-experimental test
-computer simulation
Fulvio Ricci
ILIAS
Novenber, 02 2004
Operation of the Cryomech
PTR
Cold head of
the
Pulse Tube
Refrigerator\
From
Cryomech
Thermal
shields and
vacuum
chamber of
the PTR
cryostat
Fulvio Ricci
ILIAS
Novenber, 02 2004
PTR ready for
cooling
Cooling with PTR the CaF2 mirror sample
Diameter 100 mm
Thickness 30 mm
Suspended using four thin (0.4 mm) copper wire
(electrolytic grade)
The heat is extracted through the suspension
Fulvio Ricci
ILIAS
Novenber, 02 2004
Experimental Data
I stage Extracted Power = 0
II stage Extracted Power = 0
Fulvio Ricci
ILIAS
Novenber, 02 2004
Finite Element Simulation of the system
•Material properties vs temperature:
Copper screens (gold coated), CaF2 mirror
copper wires,
• Residual thermal inputs
• Thermal boundary resistance
• Refrigeration Power
Q 
Rbd
A
Fulvio Ricci
ILIAS
A
T
Rbd
30 K 4cm 2 
 3

T  W 
From measurements
Novenber, 02 2004
Typical value
for metal-dielectric
contact
Thermal properties vs temperature
Fulvio Ricci
ILIAS
Novenber, 02 2004
Boundary conditions: definition of the heat flows
• The extracted powers
at each stage depend on
both the temperatures of
the stages themselves.
Fulvio Ricci
ILIAS
Novenber, 02 2004
Thermal load & thermal gradients
Fulvio Ricci
ILIAS
Novenber, 02 2004
Fulvio Ricci
ILIAS
Novenber, 02 2004
Cryogenic facility development
Refrigeration system study:
Vibration Free Cryostat (V.F.C.)
Fulvio Ricci
ILIAS
Novenber, 02 2004
Cool down without liquid helium:
the Pulse Tube Cryocooler
• 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.
Fulvio Ricci
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.
Novenber, 02 2004
The simpler 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
Fulvio Ricci
ILIAS
Novenber, 02 2004
Our solution: the Vibration Free Cryostat


Active vibrational
isolation system for
the heat link
Shorter heat link
Refrigerating power
preserved
V.F.C.
Spring
It is necessary to monitor
the vibration at low
temperature and to act
refrigerator:

Accelerometers and
position sensing
devices;

Actuators;
Fulvio Ricci
ILIAS
Novenber, 02 2004
Sumitomo cryocooler
Cooling capacity
1st stage 10W/20W @
45 K (50/60 Hz)
2nd stage 0.5W/0.5W
@ 4.2 K (50/60 Hz)
Lowest temperature
<0.3 K
V.F.C.
Fulvio Ricci
ILIAS
Novenber, 02 2004
Displacement noise of the cold stage
Vertical displacement
Fulvio Ricci
ILIAS
Sensor noise
Horizontal displacement
Novenber, 02 2004
V.F.C.
Fulvio Ricci
ILIAS
Vibration Free Cryostat:
first mechanical assembling
Novenber, 02 2004
3
2
1
1)
The springs and skeleton
2)
The Al inner vacuum chamber
3)
The model of the gelly fish for
4
V.F.C.
thermal contact
4)
The special bellow
Fulvio Ricci
ILIAS
Novenber, 02 2004
Work in progress
PT Refrigeration system : set up of the vibration
compensation system.
-mechanical transfer function measurements
- noise characterization to be completed in the low
frequency region
-filter design
The PT Refrigeration system will be used to study the thermal
properties of the materials candidates for the mirrors of a cryogenic
interferometer and also of the e.m. actuators which can be used at
low temperatures.
Fulvio Ricci
ILIAS
Novenber, 02 2004
Cryogenic Instrumentation for the
monitor and control
- capacitive accelerometer for low frequency
range
- accelerometer for high frequency
capacitive
piezo
-displacement sensor
Fulvio Ricci
ILIAS
Novenber, 02 2004
High frequency accelerometer
Capacitive transducer
With one vibrating plate
ft ~ 2 kHz
Vbias = 450 Volt
Ct ~ 800 pF
Elastic beams
Moving plate
Fixed plate
Gap ~ 80 mm
Room temperature calibration
by means of a
B&K pz-accelerometer
Fulvio Ricci
ILIAS
Low frequency cut-off ~10 Hz
limited by the low input
impedance of the voltage
amplifier (~20 MW)
Novenber, 02 2004
Acceleration Noise
Frequency [Hz]
Fulvio Ricci
ILIAS
Novenber, 02 2004
Vibration measurements performed on the CRYOMECH refrigerator
cold stage with piezo-accelerometers at low temperature
• Sharp peak at 1.4Hz due to the gas pulse in the cold stage
• Total displacement higher than the measurement on the Sumitomo PT.
T. Tomaru et al. Cryogenics, 44 (2004)
High frequency displacement structure probably due to the resonance of the
cryostat
•
Fulvio Ricci
ILIAS
Novenber, 02 2004
Accelerometer built in Pisa
(A. Bertolini, R. De Salvo,
F. Fidecaro A . Takamori :
IEEE Trans. in preparation)
and…….cooled in Roma
Accelerometer for very low
frequency range (Characteristic
frequency 0.5 Hz)
Fulvio Ricci
ILIAS
Novenber, 02 2004
Monitor of the resonance frequency of the accelerometer.
Her Q is limited by recoil effect of its support
Fulvio Ricci
ILIAS
Novenber, 02 2004
Position sensor :
the optical fiber bundle
Material: optran silica for broad
temperature range
Protection: PVC or s.s.
Laser source : 638 nm
Target: polished surface
Photodiode
Target
Laser
Fulvio Ricci
ILIAS
Novenber, 02 2004
Conclusions
-Payload Design: we are tuning the ANSYS simulation
program.We need to move it on a farm.
Experimental activity: thermal data collection
-Cancellation of the extra-noise vibration associated to the
cooling system: first mechanical assembly of the Vibration
Free Cryostat
-Cryogenic Instrumentation: tests at cryogenic
temperatures.
Fulvio Ricci
ILIAS
Novenber, 02 2004