Fountain effect pump driven helium flow at steady and unsteady heat load

An experimental helium II flow loop with a self-sustained fountain effect pump (FEP) is studied for various operating conditions. The regular operation is shown to be well predictable for a wide range of pressures and steady state heat loads. Special attention is drawn to its operation at various extreme conditions such as very small and very high heat load, sudden change of heat applied in the middle of the test section, and to operations at temperature and pressure limits of the pump. In most cases, temperature peaks due to sudden disturbances disappear without the need of any active control, but there are also conditions where the system is driven into oscillatory modes. The respective ranges are mapped. It is shown that such oscillations can be prevented by simple means. With respect to technical applications, it can be argued that such systems do not run out of control even when operated at extreme conditions. 5 refs