Efficiency of cooling by adiabatic melting of solid 4He in liquid 3He

LTL Quantum Physics Seminar (Nanotalo). Speaker: Mr. Tapio Riekki (Aalto Univesity, Finland).

Adiabatic melting of solid 4He in liquid 3He is a novel cooling method that overcomes the thermal boundary resistance limiting other cooling methods when trying to reach ultra low temperatures in helium isotope mixtures. We present the results of our studies, where the melting processes were started at about 10 mK , and we ended up with temperatures slightly below the pure 3He T c . The achieved cooling factors (ratio between initial and final temperature) were at range 1.9-2.7, while the theoretically predicted maximum value is 3. A thermal model describing the heat flows in the experimental setup was constructed, and we found it to be in good agreement with experimental data. We also report improved superleak behavior, and increased amount of solid compared to the earlier adiabatic melting experiment, as well as present the new experimental cell arrangement that enables better control over thermal contact between the cell and the precooler.