Tuning Fork Viscometry in Liquid Helium Matt Jachowski AJ Kumar Naveen Sinha Aaron Ligon John Rutherford Ed Fei TA: Charis Quay Physics 108, Group 4

Outline  Motivation  Experimental Setup  Results  Discussion

Why Liquid Helium?  Superfluid transition Viscosity goes to zero  Existing LHe viscometers Vibrating wire Torsional oscillator MEMS cantilever

Why Tuning Forks?  Advantages of tuning forks Crystal acts as both actuator and sensor No optical measurements necessary Crystals are inexpensive and easy to obtain  Study properties of piezoelectric crystals at low temperatures 5 mm

Design and Construction  Three environments Open in LHe Sealed in LHe Open in vacuum  Two stages  One stick The Stick and Vacuum Chamber

The Inner Stage The Outer Stage Design and Construction  Three open forks  Thermal contact to walls of can  Si diode thermometer  In vacuum  Mixture of open and sealed forks  DIP socket for modularity  In direct contact with LHe

Electronics  Excite tuning fork crystal with random noise  Measure tuning fork spectral response Preamp

Circuit Diagram Tuning Fork Adjustable Capacitor Output White noise Transformer Pre-amp

Data Collection

Tuning Fork Resonance: The Movie Open Tuning Fork

Resonant Frequency

Resonance Width

Quality Factor

Applications  Already shown to be an indicator for passing T λ / K  Viscometry and density measurement  Several theories Kanazawa and Gordon (1985): Zhang (2001):

Applications (cont’d)  There are (complicated) functional forms for density of liquid helium: Donnelly and Barenghi (1998):  Practicality of tuning fork viscometry Density Viscosity

Conclusions  Demonstration of novel LHe viscometry technique  Clear indicator of lambda transition  Future work: Closer examination of lambda transition regime Determination of proper theoretical model Real-time extraction of resonance characteristics

The End