Validation of field cage and cathode for low radioactivity operation with the CYGNO experiment

TL;DR

This work validates low-radioactivity internal components for the CYGNO-04 detector by testing multiple field cage and cathode configurations in a GIN prototype. Through stability, collection-efficiency, diffusion, and x-y uniformity measurements under a 1 kV/cm drift field and 440 V per GEM, the Nylon6-supported field cage (P3) emerges as the optimal design, offering minimal dead area and reliable performance. Measured diffusion aligns with Garfield simulations, and high detection efficiency is maintained away from edges, confirming the approach's viability for scalable, radiopure CYGNO detectors. The study also highlights engineering challenges in the aluminumized mylar cathode's electrical connections, underscoring areas for improvement before full-scale deployment in CYGNO-04.

Abstract

Dark matter, which is considered to account for approximately the 27% of the Universe's energy-mass content, remains an open issue in modern particle physics along with its composition. The CYGNO Experiment aims to exploit an innovative approach applied to the direct detection search of low energy nuclear recoils possibly induced by cold particle-like dark matter candidates. CYGNO employs a directional detector based on a Time Projection Chamber (TPC) filled with a He:CF$_{4}$ gas mixture and equipped with an optical readout. Currently, the CYGNO Collaboration is constructing the detector demonstrator, CYGNO-04, in Hall F at Laboratori Nazionali del Gran Sasso (LNGS). This 0.4 m$^3$ detector has the goal of proving the scalability of the technology and assessing the physics and radiopurity capabilities. Given the low radioactivity requirements, especially in internal components such as field cage and cathode, the reduction of material while keeping the correct electrical behavior is paramount. In this paper, we present the validation of several internal components, mainly focusing on the field cage material and support structure. The tests included geometrical asymmetries in the electric field response, collection efficiency as well as measurement of known physical quantities. A preferred configuration is found with a structure based on Nylon material which supports a PET or Kapton sheet with copper strips deposited on.

Figures (6)

• Figure 1: On the left is shown a cross section of the GIN detector design with the main components highlighted, on the right and exploded view of the internal part of the detector.
• Figure 2: On the left, the F1 field cage structure encased in the PMMA gas tight vessel, while on the right the F2 is shown. Both are equipped with cathode C1.
• Figure 4: Example of Fe clusters selection with the GIN detector. In orange, the selected iron clusters used for evaluating the collection efficiency.
• Figure 5: FC map of the P1 configuration.
• Figure 6: (left) Relative detection efficiency as a function of the source position. (right) Diffusion as a function of the source position. The points represent the measured values. The colored lines in the right plot show the best-fit curves.