Abstract
The ICARUS T600 detector, the largest liquid Argon Time Projection Chamber (LAr-TPC) realized after many years of R&D activities, was installed and successfully operated for 3 years at the INFN Gran Sasso underground Laboratory. One of the most important issues was the need of an extremely low residual electronegative impurity content in the liquid Argon, in order to transport the free electrons created by ionizing particles with very small attenuation along the drift path. The solutions adopted for the Argon recirculation and purification systems have permitted to reach impressive results in terms of Argon purity and a free electron lifetime exceeding 15 ms, corresponding to about 20 parts per trillion of O2-equivalent contamination, a milestone for any future project involving LAr-TPCs and the development of higher detector mass scales.
Highlights
2014 JINST 9 P12006 beginning of the first surface test run of one half of the T600 (275 m3) [2], an electron lifetime of 1.8 ms was observed
The ICARUS T600 detector consists of a large cryostat filled with about 760 tons of ultra-pure liquid Argon and split into two identical, adjacent modules
The through going cosmic rays collected at the rate of ∼ 3100 muons per day have been used to measure the free electron lifetime in the ICARUS-T600 providing an almost ideal source of continuous calibration
Summary
The ICARUS T600 detector consists of a large cryostat filled with about 760 tons of ultra-pure liquid Argon and split into two identical, adjacent modules. A uniform electric field (Edri ft = 500 V/cm) drifts ionization electrons with vD ∼ 1.6 mm/μs velocity towards the anode, consisting of three wire arrays and a stereoscopic event reconstruction. The first two wire planes (Induction and Induction2) record signals in a non-destructive way; the ionization charge is collected and measured on the last plane (Collection). The electronics was designed to allow continuous read-out, digitization and independent waveform recording of signals from each wire of the TPC. One thermal insulation vessel surrounds the two modules: between the insulation and the aluminium containers a thermal shield is placed, with boiling Nitrogen circulating inside to intercept the heat load and maintain the cryostat bulk temperature uniform (within 1 K) and stable at 89 K. Convective motions induced by heat losses from the module walls ensure a fast and almost complete LAr mixing, minimizing the fluctuations of the relevant parameters, such as LAr density, temperature and purity
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