Mechanical and process design of the interface to a 20,000 liter liquid helium dewar

Abstract

A new 20,000-liter (20 kL) liquid helium dewar is being integrated in to the existing cryogenic system at the Facility for Rare Isotope Beams at Michigan State University (MSU-FRIB). This dewar will mainly be used for the helium inventory management at FRIB (preserving helium inventory during unplanned / planned maintenance of the cryogenic system) and also in sharing the capacity to support the various cryogenic refrigeration systems to increase the operational efficiency and availability. It is also designed to interface to future cryogenic system upgrades (i.e., new 4.5 K refrigerators). This dewar has a single large penetration, or ‘neck’, that all the process lines and instrumentation pass through. On top of the ‘neck’ is a vacuum insulated interface box, or ‘neck can’, which houses all the connections between the dewar and the connecting distribution system. Though not generally common, this design approach has been successfully implemented on 5 to 10 kL liquid helium dewars at the Spallation Neutron Source (SNS), Jefferson Lab (JLab), and also at FRIB. It has been found that this approach greatly simplifies the mechanical design, while allowing for multiple process and instrumentation interfaces and still permitting a low heat in-leak. This paper presents an overview of the mechanical and process design of this neck can.