Design of GRETA Cooling Systems

The Gamma-Ray Energy Tracking Array (GRETA) is a full 4π gamma-ray tracking detector capable of reconstructing the energy and three-dimensional position of gamma-ray interactions within a compact sphere of high-purity germanium crystals. The GRETA Detector Array Sphere will have the capacity to accommodate a total of 30 Germanium Quad Detector Modules (QDM). The 30 QDMs are to be cooled and maintained below 100 K using liquid nitrogen (LN) at all times while the array is in normal operation, and will require regular filling of a LN Dewar on each module. The Dewar is designed to allow the Quad Module to be operated in any orientation with a LN holding time of no less than 12 hours when the detector module is fully powered. An automated LN cooling and refilling system is required to supply LN to the 30 QDMs and ensure them maintained below 100 K. Each of the GRETA QDMs houses a total of 148 pre-amplifier units within the module, and with the high power consumption of each pre-amplifier, active cooling of the pre-amplifier compartment is required. Additionally, each Quad Module will have 4 digitizer modules attached to it, which generate heat and require cooling as well. A closed-loop liquid (Glycol) cooling system will provide the required temperature stability and dissipate power generated heat for electronics. This paper presents design of the GRETA LN cooling system for detectors and the closed-loop liquid cooling system for electronics including technical requirements, design schemes, key components, operation modes, and so on.