First Commissioning of a Cryogenic Distillation Column for Low   Radioactivity Underground Argon
  We report on the performance and commissioning of a cryogenic distillation column for low radioactivity underground argon at Fermi National Accelerator Laboratory. The distillation column is designed to accept a mixture of argon, helium, and nitrogen and return pure argon with a nitrogen contamination less than 10 ppm. In the first commissioning, we were able to run the distillation column in a continuous mode and produce argon that is 99.9% pure. After running in a batch mode, the argon purity was increased to 99.95%, with 500 ppm of nitrogen remaining. The efficiency of collecting the argon from the gas mixture was between 70% and 81%, at an argon production rate of 0.84-0.98 kg/day. 
H. O. Back, T. Alexander, A. Alton, C. Condon, E. de Haas, C.   Galbiati, A. Goretti, T. Hohmann, An. Ianni, C. Kendziora, B...
astro-ph.IM hep-ex