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Description
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. GRETA will be key instrument for the Facility for Rare Isotope Beams (FRIB) with its unprecedented combination of full solid-angle coverage and high efficiency, good background rejection, and excellent energy and position resolution, and will advance the rare-isotope science at the FRIB. The GRETA Detector Array Sphere will have the capacity to accormodate 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 LN dewar is connected to a common cooling plate to which the detectors are attached. 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 Quad Modules and ensure them maintained below 100 K. Each of the GRETA Quad Modules 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. In addition to the pre-amplifiers, each Quad Module will have 4 digitizer modules attached to it, which generate heat and require cooling as well. The cooling system for GRETA electronics not only removes excess heat, but also provides the required gain stabilization of the electronics systems. A closed-loop liquid cooling system will provide the required temperature stability and dissipate power generated heat. This paper presents design of the LN cooling system for GRETA QDMs and the closed-loop liquid cooling system for GRETA electronics including techincal requirments, design schemes, analyses of heat loads and process parameters, operation modes and so on.
