Design study for ET3rd generation

Gravitational Wave Interferometer

Work Package 2

Suspension, Thermal noise and Cryogenics

Design study for ET3rd generation

Gravitational Wave Interferometer

Work Package 2

Suspension, Thermal noise and Cryogenics

Piero Rapagnani

e-mail: piero.rapagnani@roma1.infn.it

Piero Rapagnani

e-mail: piero.rapagnani@roma1.infn.it

Contract NumberRII3-CT-2004-506222

The Challenge: Find a way to push the sensitivity of a gw detector as near as possible to 1 Hz

Underground

Passive and active seismic attenuation

Low dissipation materials for mirror suspensions

Cryogenics

B 1.3.4.2: WP 2 description Work package number

2 Start date or starting event: M2

Work package title Suspension requirements characteristics Activity type: RTD Participant number 1 2 3 4 5 6 Person-months per participant

18 69 0 28 0 41

Objectives: Definition of the requirements of the optics suspension in terms of seismic isolation, mechanical losses and thermal conduction. Conceptual design of the suspension

Partecipants:1 - EGO (FRA-ITA)2 - INFN (ITA) (GE, FI, NA,PI, PG, RM1, RM2)3 - MPG (DEU)4 - CNRS (FRA)5 - University of Birmingham (UK)6 - University of Glasgow (UK)7 - VU (NL)8 - University of Cardiff (UK) + Science Team

P. Rapagnani

Thermal Noise Requirements for the Suspensions of the 3rd Gen ITF - Task ID 18

Material Intrinsic losses requirements at low temperatures

Seismic Attenuation Requirements of the suspension (100 days – M15) Suspension seismic attenuation requirements (input from site selection) Identification of control strategy and optimal mode frequencies for suspension elements

Preliminary Conceptual Design of the overall Cryogenic Suspension (360 days – M24)

Upper Suspension preliminary Design:

Active vs. Passive Super Attenuator (4 Months) Conceptual design of damping, alignment and control strategy (12 Months) Cryogenic compatibility of Upper Suspension Design (12 Months)

Last Stage Suspension Preliminary Design (300 days - M24) Test Mass Requirements (3 Months – M13) Test Mass Definition (4 Months – M23) Suspension Wires material and size choice (Input from Material Selection) Definition of last stage actuation strategy and technology

Cooling Requirements and Cooling Strategy definition (360 days - M26) Thermal Path definition and Thermal Links Requirements (6 Months - M21) Thermal Links Conceptual design (6 Months – M26)

Finalization of the Conceptual Design of the Overall Cryogenic Suspension

Month 1-33

Month 1-12

Month 1-15

Month 10-26

Month 12-26

Month 10-24

Month 10-26

Month 26-33

P. Rapagnani

Material Intrinsic losses requirements at low temperatures (12 Months – M12)Identify the materials with best properties for:

Mirror Bulk, Mirror Coating, Mirror Suspension Wires

Quantify the constraints from the thermal, optical and anelastic point of view and identify

possible tradeoffs.

Identify a possible R&D path to materials selection.

Seismic Attenuation Requirements of the suspension (100 days – M26) Suspension seismic attenuation requirements (3 Months – M26) (input from site selection)

Identification of control strategy and optimal mode frequencies for suspension elements

An extended simulation of the suspension must be developed, where the best control strategy can

be identified and tested.

It is necessary to verify that the system has no mechanical modes which involve critical degrees

of freedom and are not sensitive to the foreseen control loops.

P. Rapagnani

Preliminary Conceptual Design of the overall Cryogenic Suspension (12 Months – M23): Upper Suspension preliminary Design: Active vs. Passive Super Attenuator (4 Months) Conceptual design of damping, alignment and control strategy (12 Months) Cryogenic compatibility of Upper Suspension Design (12 Months)

Identify the constraints on the upper suspension elements due to the connection with the low temperature last stage elements. Identify a suspension interface between last stage element and suspension chain which minimize thermal conduction.

Last Stage Suspension Preliminary Design Test Mass Requirements (460 days – M22) Test Mass Geometry and Size definition (Input from Optical Configuration) Test Mass Mechanical and Optical losses requirements (12 Months – M12) Test Mass Definition (4 Months – M23) Suspension Wires material and size choice (Input from Material Selection) Definition of last stage actuation strategy and technology Actuation and Sensing at low temperatures allow the use of superconducting

techniques which are the lowest noise technologies available, at the cost of an increased complexity of the system and of the necessity to be at low temperatures to make it work. It is possible to design hybrid systems which could have traditional sensing and actuation, working also at room temperature, in parallel with superconducting low noise sensors, which could be used once the proper operating point of the antenna is reached.

P. Rapagnani

Cooling Requirements and Cooling Strategy definitionIdentify the requirements on test mass temperature in order to have a negligible thermal noise,

with respect to seismic, newtonian and radiation pressure noises.

Identify the best cooling strategy (refrigeration only, cryogenic liquids, hybrid techniques)

regarding:

underground facilities safety and costs (input from site selection),

power to extract from the test mass (input from mirror optical properties)

noise input constraints

Thermal Path definition and Thermal Links Requirements

Identify the best possible path depending on the cooling strategy: tradeoff between the

necessity to have a short thermal link and a very low frequency, (hence very long)

connection of the mirror to the refrigeration apparatus.

Identify the constraints on the acoustic attenuation chain for the thermal links.

Thermal Links Conceptual design (3 Months – M24)

Finalization of the conceptual design of thermal links attenuation chain, i

including the thermal contacts between refrigeration apparatus and last

stage elements.

P. Rapagnani

Following the approval of the ET Design Study:

Definition of tasks and tasks responsibles together with involved groups

Kick-off meeting of the WP2 activity

Periodic (bimonthly?quarterly?) meetings

Encourage exchanges and coordination betweenThe involved groups and with other groups in the Science Team

P. Rapagnani

The Prototype The Prototype of Cryogenic Payloadof Cryogenic PayloadThe Prototype The Prototype of Cryogenic Payloadof Cryogenic Payload

We have designed and built a We have designed and built a cryogenic payload scaled 1:3.5 cryogenic payload scaled 1:3.5 compared to the VIRGO standard compared to the VIRGO standard

Marionette hosting the central insert made Marionette hosting the central insert made of silicon (at present the central insert is of silicon (at present the central insert is made of Al)made of Al)

Reaction mass of the mirror Reaction mass of the mirror made of copper, gold coatedmade of copper, gold coated

Mirror suspended by silicon strips attached Mirror suspended by silicon strips attached with silica bonding with silica bonding

(Present suspensions are copper strips)(Present suspensions are copper strips)

Mirror suspended by silicon strips attached Mirror suspended by silicon strips attached with silica bonding with silica bonding

(Present suspensions are copper strips)(Present suspensions are copper strips)

Silicon mirror (Preliminary Silicon mirror (Preliminary assembly with a fake assembly with a fake aluminum mirror)aluminum mirror)

Electromagnetic actuators like Electromagnetic actuators like the Virgo mirrors lateral ones the Virgo mirrors lateral ones (macor support, copper wire (macor support, copper wire kapton insulated)kapton insulated)

P. Rapagnani

10-9

10-7

10-5

10-3

10-1

101

0 1 2 3 4 5

Hz

PSD (Horizontal displacement) PSD (Vertical displacement)Fiber Bundle (Sensor used also at low temp.)

V/ Hz2

10

10-

1

10-

3

10-

5

10-

7

10-

9

10

10-

1

10-

3

10-

5

10-

7

10-

9

Frequency [Hz]Frequency [Hz]

October, 27 2006October, 27 2006Paola PuppoPaola Puppo

ILIAS Meeting - LondonILIAS Meeting - London 1010

Minipayload Minipayload Mechanical Mechanical

ModesModes(room temperature (room temperature

measurements;measurements;Noise injected by coils)Noise injected by coils)

sensor monitoring the sensor monitoring the mirror positionmirror position

Minipayload Minipayload Mechanical Mechanical

ModesModes(room temperature (room temperature

measurements;measurements;Noise injected by coils)Noise injected by coils)

sensor monitoring the sensor monitoring the mirror positionmirror position

Torsional mode

Pendulum mode

V/(Hz)1/2V/(Hz)1/2

P. RapagnaniOctober, 27 2006October, 27 2006 1111

Cooling test on the small scale payload prototype

0

50

100

150

200

250

300

0 50 100 150 200 250 300

2 (First Cold stage)3 (Second Cold Stage)10 (Mirror)11 (Reaction Mass)

Temperature (K)

Hours

Fiber Bundle Sensor

P. Rapagnani1212

Next stepsNext stepsNext stepsNext steps Improve the vibration reduction schemeImprove the vibration reduction scheme To modify the sensing scheme to improve the noise floor at closed loop to To modify the sensing scheme to improve the noise floor at closed loop to

the control of the horizontal degrees of freedom ;the control of the horizontal degrees of freedom ; Full scale cryogenic payload (with silicon)Full scale cryogenic payload (with silicon)

Test a full scale silicon mirror at cryogenic temperature in Test a full scale silicon mirror at cryogenic temperature in the EGO cryostat in Cascina, Virgo Site;the EGO cryostat in Cascina, Virgo Site;

To define in a realistic way the refrigeration procedureTo define in a realistic way the refrigeration procedure The properties of the full scale silicon mirror.The properties of the full scale silicon mirror.

Improve the vibration reduction schemeImprove the vibration reduction scheme To modify the sensing scheme to improve the noise floor at closed loop to To modify the sensing scheme to improve the noise floor at closed loop to

the control of the horizontal degrees of freedom ;the control of the horizontal degrees of freedom ; Full scale cryogenic payload (with silicon)Full scale cryogenic payload (with silicon)

Test a full scale silicon mirror at cryogenic temperature in Test a full scale silicon mirror at cryogenic temperature in the EGO cryostat in Cascina, Virgo Site;the EGO cryostat in Cascina, Virgo Site;

To define in a realistic way the refrigeration procedureTo define in a realistic way the refrigeration procedure The properties of the full scale silicon mirror.The properties of the full scale silicon mirror.

P. Rapagnani1313

Cryo-Compatible Superattenuator design Cryo-Compatible Superattenuator design Cryo-Compatible Superattenuator design Cryo-Compatible Superattenuator design Pintracavity= 500 kWcoating=1ppmPcoating=500 mW

•High Thermal impedance MRM wire

•The upper part is thermally insulated by thermal screens