Cryostats for a Liquid Argon “Near Detector” in a Neutrino Beam

This note sketches some preliminary specifications for the cryostats for liquid argon (density ρ = 1.396 g/cm, T = 87 K) time projection chambers of active mass in the range 40-333 metric tons, as would be suitable for use as “near detectors” in a neutrino beam such as the NuMI beam now under construction at Fermilab. A major cost driver of such a detector is its cryostat, which will have to be delivered in pieces to the underground site, and welded together in situ. An important constraint on the assembly of the detector is the size of the access shaft through which the parts must be delivered. Here, we use the dimensions of the vertical access shaft, shown in Fig. 1, to the NuMI/MINOS Near Detector Hall which is about 350′ underground, as shown in Fig. 2. Nominally, the largest rectangular aperture in the shaft is 1.75× 6.4 m. In this note, we suppose that this restricts components to have a maximum cross section (in the horizontal plane) of 1.5× 6 m.