T-lambda depression in He-4 by a heat current along the lambda-line

We report measurements of the depression of the superfluid transition tempe rature by a heat current (1 less than or equal to Q less than or equal to 1 00 mu W/cm(2)) along the lambda-line (SVP less than or equal to P less than or equal to 21.6bar). Experimental data can be represented by Delta T-lamb da/T-lambda = (Q/Q(0))(x). The exponent, x, is universal and pressure indep endent as expected, but its value (about 0.9) is higher than the theoretica l prediction (0.745) and the earlier experimental value (0.813) at SVP. The amplitude, Q(0), shows a pressure dependence that is in qualitative agreem ent with the theoretical prediction, but its value is lower than the predic ted and earlier experimental values at SVP. At P = 21.6 bar, measurements w ere also performed in a reduced effective gravity (0.2g), and these results show that the gravity effect in our measurements is small. Published by El sevier Science B.V.