Gaseous Argon Optical Time Projection Chamber Technology Demonstration for the Deep Underground Neutrino Experiment (DUNE) Near Detector

The Deep Underground Neutrino Experiment will study neutrinos produced from a high-intensity beam, that will travel a distance of over 1,300 km. One component of the near detector site that will be located less than 600 m from the source of the beam is ND-GAr, a high-pressure gaseous argon-based Time Projection Chamber. GAT0 is the name of a prototype of ND-GAr being developed to demonstrate event time-tagging with primary scintillation light that is produced after particle interactions, and imaging of ionisation tracks. By doping argon with 1% of CF4, scintillation light is wavelength-shifted from the VUV to the visible region centred at λ= 630 nm, a region that is easier to detect with readily available photosensors.

Imaging of alpha particle ionisation tracks from secondary scintillation light in GAT0 is demonstrated by instrumenting two layers of micropatterned charge amplification structures - thick Gaseous Electron Multipliers - operated in 1 bar of Ar:CF4 at a concentration of 99:1.

Primary scintillation light will be used to record the absolute time of interactions and will be detected with a plane of SiPM photosensors. The time resolution of the photosensor limits how precisely this information can be retrieved. A front-end readout electronics board that combined the readout of 16 channels of the Hamamatsu S14161-6050HS-04 SiPM tile to pave the way for large-area coverage was developed for GAT0. Experimental results show a signal-to-noise ratio of 7 and a dark count rate of ∼500 at -35 °C.

A layer of reflective PTFE material is placed surrounding the inner surface of GAT0, to increase the light collection efficiency. Photon propagation simulations were carried out in Geant4 with a range of PTFE reflectance values, and two scenarios of SiPM area-coverage are presented.