Autonomous RPCs for a Cosmic Ray ground array

TL;DR

This paper presents the development and field testing of robust, low-maintenance Resistive Plate Chambers (RPCs) for muon detection in ultra-high energy cosmic ray experiments, demonstrating stable operation over two years.

Contribution

It introduces a new RPC design optimized for outdoor UHECR experiments, capable of low gas flux operation and reliable long-term performance in harsh environments.

Findings

RPCs operated stably for over 2 years in field conditions

Low gas flux operation enables multi-year use with small reservoirs

Compact, sealed design suitable for remote outdoor deployment

Abstract

We report on the behaviour of Resistive Plate Chambers (RPC) developed for muon detection in ultra-high energy cosmic ray (UHECR) experiments. The RPCs were developed for the MARTA project and were tested on field conditions. These RPCs cover an area of $1.5 \times 1.2\,{m^2}$ and are instrumented with 64 pickup electrodes providing a segmentation better than $20\,$cm. By shielding the detector units with enough slant mass to absorb the electromagnetic component in the air showers, a clean measurement of the muon content is allowed, a concept to be implemented in a next generation of UHECR experiments. The operation of a ground array detector poses challenging demands, as the RPC must operate remotely under extreme environmental conditions, with limited budgets for power and minimal maintenance. The RPC, DAQ, High Voltage and monitoring systems are enclosed in an aluminium-sealed case, providing a compact and robust unit suited for outdoor environments, which can be easily deployed and connected. The RPCs developed at LIP-Coimbra are able to operate using a very low gas flux, which allows running them for few years with a small gas reservoir. Several prototypes have already been built and tested both in the laboratory and outdoors. We report on the most recent tests done in the field that show that the developed RPCs have operated in a stable way for more than 2 years in field conditions.