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A BSTRACT : The accumulation of positive ions, produced by ionizing particles crossing Liquid Argon Time Projection Chambers (LAr-TPCs), may generate distortions of the electric drift field affecting the track reconstruction of the ionizing events. These effects could become relevant for large LAr-TPCs operating at surface or at shallow depth, where the detectors are exposed to a copious flux of cosmic rays. A detailed study of such possible field distortions in the ICARUS T600 LAr-TPC has been performed analyzing a sample of cosmic muon tracks recorded with one T600 module operated at surface in 2001. The maximum track distortion turns out to be of few mm in good agreement with the prediction by a numerical calculation. As a cross-check, the same analysis has been performed on a cosmic muon sample recorded during the ICARUS T600 run at the LNGS underground laboratory, where the cosmic ray flux was suppressed by a factor ~10 6 by 3400 m water equivalent shielding. No appreciable distortion has been observed, confirming that the effects measured on surface are actually due to ion space charge. K EYWORDS : Neutrino detectors, Noble liquid detectors, Time projection Chambers (TPC), Charge transport and multiplication in liquid media.

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The High Energy cosmic-Radiation (HERD) detector is one of the prominent space-borne instruments to be installed on-board the Chinese Space Station (CSS), around 2027. Primary scientific goals regarding this initiative include: precise measurements of cosmic ray (CR) energy spectra and mass composition, at energies up to the PeV range; contributions to high energy gamma-ray astronomy and transient studies; as well as indirect searches for Dark Matter (DM) particles via their possible annihilation/decay to detectable products. HERD is configured to accept incident particles from both its top and four lateral sides. Owing to its pioneering design, an order of magnitude increase in acceptance is foreseen, with respect to previous and ongoing experiments. The Plastic Scintillator Detector (PSD) constitutes an important sub-detector of HERD, particularly aimed towards anti-coincidence (discriminating incident photons from charged particles), while providing precise charge measurement of incoming cosmic-ray nuclei in a range of Z = 1 -26. Main requirements concerning its design, include: high detection efficiency, broad dynamic range and good energy resolution. In order to select the optimal layout, two geometries are currently under investigation: one based on long scintillator bars and the other on square tiles, with both layouts being readout by Silicon Photomultipliers (SiPMs). Ongoing activities and future plans regarding the HERD PSD will be presented in this work.