Separating $^{39}$Ar from $^{40}$Ar by cryogenic distillation with Aria for dark matter searches

Aria is a plant hosting a 350 m cryogenic iso-
\ntopic distillation column, the tallest ever built, which is being
\ninstalled in a mine shaft at Carbosulcis S.p.A., Nuraxi-Figus
\n(SU), Italy. Aria is one of the pillars of the argon dark-matter
\nsearch experimental program, lead by the Global Argon Dark
\nMatter Collaboration. It was designed to reduce the isotopic
\nabundance of 39 Ar in argon extracted from underground
\nsources, called Underground Argon (UAr), which is used for
\ndark-matter searches. Indeed, 39 Ar is a β-emitter of cos-
\nmogenic origin, whose activity poses background and pile-
\nup concerns in the detectors. In this paper, we discuss the
\nrequirements, design, construction, tests, and projected per-
\nformance of the plant for the isotopic cryogenic distillation of
\nargon. We also present the successful results of the isotopic
\ncryogenic distillation of nitrogen with a prototype plant.