The LBNE 35 Ton Prototype Cryostat

The 35 Ton Prototype Cryostat was built to demonstrate that a commercial membrane-cryostat technology could achieve the performance necessary for the operation of a large multi-kiloton liquid argon detector for the Long-Baseline Neutrino Experiment (LBNE). A concluded Phase 1 run has confirmed both the thermal stability and leak tightness of this technology that is necessary to achieve extremely pure liquid argon. Measured electron drift times in excess of 2.5 ms infer impurity concentrations in the liquid argon of less than 140 ppt (O2 equivalent). These purity levels were attained and held for sustained periods. Details of the cryostat operation, measurements, and analysis of the Phase 1 run are given. A future Phase 2 run, that will include a reduced-scale LBNE-style Time Projection Chamber with integral photon detectors is briefly described.