Helium Flow Through Filters

Abstract

In previous investigations of helium flow through filters the filter was immersed in the liquid [^1–3]. This reduced the attainable differences of pressure and temperature across the filter to a few μbar and mK. The investigations presented here were performed with a filter placed above the He II bath. Thus, the filter divided the cryostat into two chambers and only the upper side of the filter was in contact with liquid helium; the lower side on the other hand, was only in contact with the vapor of the He II bath. This arrangement permitted measurements across the filter at relatively large pressure and temperature differences.