A Miniature Second Sound Probe I - MOTIVATION & SENSORS DEVEL. PROGRAM II -2nd SOUND SENSOR IN...

A Miniature Second Sound Probe

I - MOTIVATION & SENSORS DEVEL. PROGRAM

II - 2nd SOUND SENSOR IN STATIC HELIUM

III - 2nd SOUND SENSOR IN FLOW

IV- FIRST RESULTS

Sensor validation + Preliminary physics results

Cryogenic Turbulence GroupCenter for Research on Very Low Temperature (CRTBT)

Grenoble, France

QuickTime™ et undécompresseur TIFF (LZW)

sont requis pour visionner cette image.



Motivation :scaling laws of superfluid/quantum turbulence

Approach :local & dynamical sensors for 4He above 1.3 K

T=1,4 K

T=2,3 K

T=2,08 K

Reference result :

Pitot pressure fluctuations byMaurer & Tabeling, 1998

Space resol. = 1.2mm (outer diam.)Time resol. = 1-800 Hz

Pressure sensors (under operation and/or test)

• Commercial sensor (Maurer-Tabeling’s approach) DC-1kHz bandwidth / mm spatial resolution

• Home-made silicon membrane sensor : very sensitive + differential objective : DC-few kHz bandwidth / 0.5 mm spatial resolution

Temperature sensors (under development)





objective : DC-1MHz bandwidth / few m spatial resolution

• Superconducting transition edge thermometer (Al)

• Supporting frame is a delicate issue (non invasive for the flow)

« our traditional frame » : 5m glass fiber Fully micromachined process on a Kapton membrane (under develop.)

30 m thermometer spotm thermometer spot

Flow

• T = 1.5 K superfluid ratio = 88%

• V = 0.05-1 m/s Re = V./ = 104 - 2.105 (mass flow = 40 g/s)

He IIConduite=2,cmHéliceAxeMesures Axis

propeller

local probes

pipe

(T.Didelot PhD)

Pitot tube(mean velocity)

Screens

Honeycomb

Another flow: project

NS2 bis

Ligne hauts Reynolds NEF

7

Moteur

Pompe

location : CEA Grenoble

T range : 1,5 - 4 K

Mass flow : 400g/s @ 1.5 K

600g/s for T > 1.8 K

Grid turbulence ( R~350 )

Collaboration : CEA : flow operation (Girard, Rousset,…) CRTBT : instruments (Roche, Chabaud, Hébral,

Thibault, Diribarne(PhD),Gauthier(PhD ) LEGI (Gagne, Baudet) Theoretical / Numerical :

Castaing, Barenghi, Vassilicos, Daviaud,…

Miniature second sound probe

• Attenuation ~ Vortex line density ~ (inter-vortex spacing) -2

• Anisotropic sensor

Thermometer

Heater

HELIUM FLOW

Heater and Thermometer supports

Design/micromachining :H. Willaime, P. Tabeling, Microfluidic group, ESPCIO. Français, L. Rousseau, Micromachining center, ESIEE



Effective surface=

1mm*1mm

Thermometer (Al)(transition edge ~ 1.5K)

Heater (Cr)

Side view :thermometer and heaterfacing each others

Tip thickness= 15 m

Assembling

• 4 wires measurements• Cavity size : 1mm*1mm*300m



Thickness ~ 15m

Gap ~ 300m



How to choose the Heater driving current ?

Steady counter-flow Induced turbulence ? if yes : sensor is invasive

Heater Joule effect(sin)2= DC+AC

Second soundattenuation

W

T1

T2

Superfluid / Normal

Choosing the Heater driving current

• Evidence of « T1 » transition found at expected the critical heat flux density

• Driving current was set-up below this transition (…but doesn’t seem critical)





T1 transition

laminar turbulent

Second sound resonance modeswithout flow

• Fondamental mode : f0 = 40 kHz (expected ~ V2nd son/ 2.Gap ~ 35 kHz)

• Dynamical response : n.f0 / Q > 4 kHz

• Linear propagation : sinus signal received on thermometer (negligible distorsion)

• Received signal amplitude is what we expect



Resonance modes with a flow

• Frequency shift negligeable

• Limited defocusing since Vflow << V2nd sound (and can be compensated)

• in the following, the fondamental mode of resonance was chosen



From Measured signal to Vortex Line Density (VLD)

0

2 1011

4 1011

0 1

VLDVLD linear approx

A/A0

• Based on rotating bucket experiments (Hall & Vinen 1956 , …)+ Vortex Tangle Isotropy hypothesis

• First order relation is :

VLD(t) ~ (6.f0. / B.0.Q) . (A0/A(t) -1)

with : A0/A attenuation of amplitude B mutual friction constant f0 resonant frequency Q quality factor

(general relation : for ex. see Stalp thesis, 1998)

Time / Space resolution

Electronic Bandwidth: DC-1kHzTypical velocity : 1 m/s

electronic resolution ~ (1m/s*1kHz)-1 = 1 mm ~ sensor size

Structures larger than sensor and/or slower than time of flight thru sensor

300 m

1 mm

1 mm

Acknowledgement

Colleagues :

Students :

Collaboration :

Many inputs from B. Castaing (ENS Lyon)

B. Chabaud - B. Hébral

T. Didelot (PhD), F.Muzellier, F. Gauthier

P. Tabeling, H. Willaime (ESPCI)O. Français, L. Rousseau (ESIEE)

A Miniature Second Sound Probe I - MOTIVATION & SENSORS DEVEL. PROGRAM II -2nd SOUND SENSOR IN...

Documents

Transcript of A Miniature Second Sound Probe I - MOTIVATION & SENSORS DEVEL. PROGRAM II -2nd SOUND SENSOR IN...