Design and performance of the GERDA low-background cryostat for operation in water

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