Heat Flow in a He Ii Filled Fin*

The excellent heat removal capability of pressurized superfluid helium, HeIIplVg, has led in recent years to its use as a coolant in fusionlo and acceleratorll magnets where the operating temperature is typically in the range of 1.8 to 2. K. More recently, He-IIp has been proposed as the coolant for a polarized proton target at temperatures as low as 0.5K12. In all cases the HeIIp acts as an aintermediate fluid between the heat source (magnet winding or target bead) and the heat sink (saturated He-II in the case of the magnets or saturated helium-3 in the case of the polarized proton target). The heat sink fluid may be vaporized in .a jacket external to the magnet vessel13, in a heat exchanger which is immersed in the He-IIp14, or in a separate bath in which is immersed an He-IIp filled fin which extends from the heated reservoir. In the latter configuration a single heat sink can serve multiple heat sources l5 It is this latter arrangement which . is considered here and which is pictured schematically in Fig. 1. We proceed to analyze the flow of heat in the cooled channel. This is in contrast to the considerable work which has been done for the insulated channe1.2p16-18