Abstract
We report a new thermally generated steady-state flow of He II and its decay. An upward superflow through vertical channels of a square cross section with ends blocked by sintered silver superleaks is induced by a fountain pump. On increasing the heat power Q[over ] a vortex-free superflow and, above an intrinsic critical velocity of about 1.5 cm/s, two distinctly different turbulent steady-state flows characterized by the vortex line density L proportional, variantQ[over ];{2} and L proportional, variantQ[over ] are observed using the second sound attenuation technique. When Q[over ] is switched off, after a fast initial decay an exponential decay law is observed. A simple phenomenological model is introduced, capturing the observed features.
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