Elba GWADW workshop-May 2008

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Information about Elba GWADW workshop-May 2008
Science-Technology

Published on July 8, 2008

Author: padapupps

Source: authorstream.com

Cryogenic Developments for future GW Interferometers : Cryogenic Developments for future GW Interferometers Piero Rapagnani & Paola Puppo Dipartimento di Fisica – Università di Roma “La Sapienza” INFN – Rome Elba GWDAW 2008 Why to cool the mirrors? : Why to cool the mirrors? Test masses and suspensions thermal noise reduces at low temperature: Thermoelastic noise both of the mirror substrates and coatings decrease: Thermal expansion rate a decreases at low temperature; Thermorefractive noise Losses of some materials decrease at low temperature 2 A look into the past… : A look into the past… 3 A look into the past… : A look into the past… 4 Slide 5:  The first cryogenic antenna in the world 1974-1980: M=20 kg, T =4 K , f ~ 5 kHz The second cryogenic antenna of the Rome group -1978: M~ 400 kg, T =4 K , f ~ 1.8 kHz No excess noise Excess noise in the first phase of operation Superfluid helium eliminates boiling noise :  Superfluid helium eliminates boiling noise EXPLORER T=2.1 K NAUTILUS 2.5 tons Al5056 antenna cooled at 100 mK NAUTILUS T=0.1 K Slide 7: no detector 0 days Single 0.98 days Double 21.94 days Triple 144.10 days Quadruple 243.97 days Cumulative Event Number Vs SNRAURIGA-NAUTILUS-EXPLORER-ALLEGRO Very low fraction of outliers SNR>10 Stable performances of resonant gw detectors in the long run Duty Time Slide 8: 8 Cryogenic 3° Generation GW detector --- Mirrors Thermal (Low T) --- Suspensions Thermal (Low T) --- Readout (High Power, Big masses) --- Newtonian (go underground) big mass mirrors, monolithic suspensions low T Pcavity ~ 500 kW Slide 9: … to prepare for the future: Mirror cooling techniques Payload structure Cryogenic interface with low frequency suspensions Sensors and Actuators using superconducting/cryogenic techniques: dcSQUIDs amplifiers, Superconducting pancake coils (inductive sensors) Electrostatic Cryogenic Sensors Superconduting e.m. shielding Cryo-Compatible Mirror Suspension Design : 10 Cryo-Compatible Mirror Suspension Design High Thermal impedance MRM wire (The upper part is thermally insulated by thermal screens) Cryocooler with active and passive isolation Superconducting sensors and actuators Superconducting e.m. shieldinng Crucial motivation for cryogenic application: mirror thermal lensing : Crucial motivation for cryogenic application: mirror thermal lensing Pintra = 5 kW Pcoat = 25 mW Temperature increasing Mirror center As soon as the sensitivity gets better we need a more reliable and effective thermal compensation; Temperature increasing of a Virgo-like mirror Crucial motivation for cryogenic application: mirror thermal lensing : 12 Crucial motivation for cryogenic application: mirror thermal lensing Cryo Interferometer Pcoat=0.5 W Pcavity=500kW thermal gradient The thermal lensing is likely to be negligible because the thermal expansion coefficients tend to zero at cryogenic temperatures; At cryogenic temperatures, the thermal conductivity increases and consequently reduces thermal gradients on the coating; Refraction index variation with temperature is very small at low temperature. thermal gradient on a Virgo mirror How can we cool the mirrors? (I) : How can we cool the mirrors? (I) 13 Mirror and its suspension wires: wires and mirror materials compatible with good mechanical and thermal properties; High thermal conductivities materials; Low mechanical and optical losses; a promising material both as mirror substrate and wire is silicon having high thermal conductivity very low thermal expansion (zero below 17K) Slide 14: 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; 14 How can we cool the mirrors? (Ii) Slide 15: 15 Scheme of the cryogenic payload Slide 16: 16 In 2006-2007 we cooled down a small scale payload prototype (in Rome Virgo Laboratory) We measured: Thermal behavior Mechanical behavior (fiber bundle sensor) Minipayload Mechanical Modes(room temperature measurements;Noise injected by coils)sensor monitoring the mirror position : October, 27 2006 17 Minipayload Mechanical Modes(room temperature measurements;Noise injected by coils)sensor monitoring the mirror position Torsional mode Pendulum mode VFC (Vibration Free Cryostat) scheme : 18 VFC (Vibration Free Cryostat) scheme Pulse Tube S. Caparrelli, E. Majorana, V. Moscatelli, E. Pascucci, M. Perciballi, P. Puppo, P. Rapagnani, F. Ricci "Vibration-free cryostat for low-noise applications of a pulse tube cryocooler", Rev. of Sci. Inst. 77, 095102 (2006). T. Tomaru et al. Cryogenics, 44 (2004). Slide 19: 19 Vibration of the cold head reduced (@T=4K) The vibration reduction scheme works The sensing will be modify to reduce the noise floor at closed loop. displacement noise density Slide 20: 20 2008: Full Scale Cryogenic Payload Marionetta Reaction Mass (MRM) Ti alloy cable (low thermal conductivity) Ti-6Al-4V Marionetta Mirror silicon Wires Reaction Mass high conductive wires Reaction Mass (Al Alloy) Silicon mirror Main Requirements 1. Internal frequencies as high as possible 2. Low pendulum and torsional frequencies (mirror control ). 3. Good thermal properties for cryogenic operation Slide 21: 21 Mirror Reaction Mass Main Properties 1. Supports the e.m. actuators 2. Act as thermal screen 3. Protect the mirror Made of Al alloy FEM mechanical Lowest frequency for the Mirror RM: 600 Hz Lowest frequency for the MRM: 400 Hz Slide 22: 22 MRM Main Characteristics Aluminum Alloy Cloverleaf shape Al Alloy Coil supports Slide 23: FEM study Mode 1: coil supports Mode 9 : MRM body Slide 24: 24 Marionetta Main Characteristics Lateral cuts for the insertion of the silicon wires Copper clamps Copper links with the cooler Dielectric arms epoglass FR4 (no eddy currents) No magnetic steel body 2 3 4 5 1 Marionetta internal modes Body: lowest 2300 kHz Arms: lowest 1100 Hz Slide 25: 25 We plan a first cooling of the silicon mirror using the following set-up: Silicon mirror suspended by using two copper wires loops; Marionette with copper clamps, connected to the cooler by copper heat links, suspended with a titanium alloy cable; Reaction mass of the mirror holding a fiber bundle sensor to measure the system modes (suspended with copper wires); Reaction mass of the marionette holding the Virgo-like electromagnetic actuators (macor support, copper wire kapton insulated); MRM suspended with three titanium wires; Whole payload hung to an attenuation stage (geometric antispring) (first cryogenic test of a filter with blades) First cooling of the cryogenic payload The Cryogenic Test FaciliyR. Passaquieti, F. Frasconi, A. Pasqualetti (Pisa. EGo) : 26 The Cryogenic Test FaciliyR. Passaquieti, F. Frasconi, A. Pasqualetti (Pisa. EGo) Cryostat built in Cascina (Virgo site – 1500 West Arm) Equipped with 2 pulse tube cryogenerators (1 double-stage (0.5W @ 4.5 K), 1 single stage PT60) It will host a full cryogenic payload with one attenuation stage. FEM thermal simulation : FEM thermal simulation 27 define the diameter of the copper suspension wires; draw the expected equilibrium temperature when there is a laser light on the mirror Boundary Conditions Cryocooler Second stage link to the marionetta Laser power on the mirror Gaussian beam Pabs= 1 W Pabs = 100 mW by the mirror bulk The power absorbed by the coating is dominant Starting point: termalised system at 10 K laser power on surrounding system at 10K The reaction masses are not present in the simulation; Their screen effect is simulated by the surrounding system at 10K; The marionetta arms are not present. Copper and silicon thermal properties vs temperature are included in the simulation. The mirror reaction mass will be included later to have a better evaluation of the cooling time; The model Pcooler depends on the temperature (Cryomec PT curve used) FEM thermal results : FEM thermal results To optimize the cooling time a wire diameter of 1.7 mm is chosen. The transient Thermal flux in the steady state Steady state Mirror temperature 5 K 11 K Cryo-Compatible Superattenuator design : Cryo-Compatible Superattenuator design 29 High Thermal impedance MRM wire The upper part is thermally insulated by thermal screens What is going on… : 30 What is going on… Simulation: Thermal transient study with the reaction masses; Mechanical study of the whole system with the chosen wires; First assembly test on Virgo site in mid 2008. June 2008 assembly July-September 2008 cooling.

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