Thermal Counterflow Around a Spherical Bubble Formed Due to a Hot Filament in Superfluid 4He

A thin tungsten filament glowing without boiling in helium-4 is a classic and widely used demonstration of infinite thermal conductivity of superfluidity. Under normal conditions, the filament exhibits Ohmic conductivity, referred to as "cold" state. However, this behavior abruptly changes when a helium vapor bubble forms around the filament, which is referred to as the "hot" state. The intense thermal counterflow generated by the hot filament can trigger turbulence within the superfluid. To investigate this quantum turbulence, which attenuates second sound, we constructed a second-sound resonator. A tungsten filament was positioned in the center of the resonator to create a radial thermal counterflow, serving as a source of turbulence. Our observations reveal that the attenuation of the second-sound resonance correlates with the filament’s Joule heating power. Surprisingly, quantum turbulence associated with thermal counterflow affects second-sound attenuation in markedly different ways depending on whether the filament is in the cold or hot state—even when the Joule heating power remains the same.