Experimental study of λ-phase transition induced by shock compression Original Research Article

The λ-phase transition induced by shock compression was experimentally investigated by using the superfluid shock tube facility. A compression shock wave is generated in He II by the impingement of a gas dynamic shock wave onto a He II free surface. The shock-compressed He II can be converted to He I crossing the λ-line in the case of initial He II temperature close to Tλ. The resultant temperature variation has been measured with in-house-made superconductive temperature sensors. Furthermore, the visualization photographs were taken by a digital still camera with the Schlieren optical method. It is found that the magnitude of the entropy production Δs induced by shock compression process highly depends on the temperature difference between the temperature in the shock compressed state and the lambda temperature as well as on the shock strength. In particular, Δs becomes extremely large in the case where the λ-phase transition is induced.