Design and Performance of the GERDA Low-Background Cryostat for Operation in Water

TL;DR

The paper details the design, operation, and safety considerations of the GERDA experiment's large liquid argon cryostat, which significantly reduces background noise for neutrinoless double-beta decay searches.

Contribution

It presents the first implementation and operational experience of a large cryostat immersed in water for low-background physics experiments.

Findings

Achieved background levels below 10^{-3} cts/(keV·kg·yr)

Demonstrated safe operation of a large cryostat in a water tank

Validated the shielding concept for future low-background detectors

Abstract

In searching for the neutrinoless double-beta decay of $^{76}$Ge the GERmanium Detector Array (GERDA) experiment at the INFN Laboratori Nazionali del Gran Sasso has achieved an unprecedented low background of well below 10$^{-3}$ cts/(keV$\cdot$kg$\cdot$yr) in the region of interest. It has taken advantage of the first realization of a novel shielding concept based on a large cryostat filled with a liquid noble gas that is immersed in a water tank. The germanium detectors are operated without encapsulation in liquid argon. Argon and water shield the environmental background from the laboratory and the cryostat construction materials to a negligible level. The same approach has been adopted in the meantime by various experiments. This paper provides an overview of the design and operating experience of the 64 m$^3$ liquid argon cryostat and its associated infrastructure. The discussion includes the challenging safety issues associated with the operation of a large cryostat in a water tank.