Depression of the Superfluid Transition Temperature in ⁴He by a Heat Flow

The depression of the superfluid transition temperature in He by a heat flow Q is studied. A small sealed cell with a capillary is introduced and a stable and flat superfluid transition temperature plateau is easily obtained by controlling the temperature of the variable-temperature platform and the bottom chamber of the sealed cell. Owing to the depression effect of the superfluid transition temperature by the heat flow, the heat flow through the capillary is changed by the temperature control to obtain multiple temperature plateaus of different heat flows. The thermometer self-heating effect, the residual heat leak of the 4.2 K environment, the temperature difference on the He II liquid column, the Kapiza thermal resistance between the liquid helium and the copper surface of the sealed cell, the temperature gradient of the sealed cell, the static pressure of the He II liquid column and other factors have influence on the depression effect and the influence is analyzed in detail. Twenty experiments of the depression of the superfluid transition temperature in ⁴He by heat flow are made with four sealed cells in one year. The formula of the superfluid transition temperature pressured by the heat flow is T_λ(Q)=?0.00000103Q+2.1769108, and covers the range 229≤Q≤6462 μW/cm².