Development of a high-rate capable DLC-RPC based on a current evacuation pattern

TL;DR

This study develops a DLC-RPC detector with a current evacuation pattern for high-rate environments, achieving up to 60% efficiency but facing discharge stability issues that need further investigation.

Contribution

It introduces a novel current evacuation pattern and protection cover design for DLC-RPCs to improve high-rate detection performance.

Findings

Detection efficiency reached approximately 60% for beta rays.

Voltage drops of 100-150 V still allow target efficiency.

Discharges occurred after hours, causing operational issues.

Abstract

A Resistive Plate Chamber using Diamond-Like Carbon electrodes (DLC-RPC) has been developed as a background tagging detector in the MEG$~$II experiment. The DLC-RPC is planned to be installed in a high-intensity and low-momentum muon beam. This detector is required to have a detection efficiency above 90 % with four active gaps in the muon beam due to the limitation of the material budget. In such an environment, the high current flowing through the resistive electrodes causes a voltage drop, which reduces the performance of the DLC-RPC. This voltage drop can be suppressed by implementing a current evacuation pattern, though discharges are more likely to occur near the pattern. Therefore the pattern must be covered by a protection cover made of an insulator. In this study, electrode samples with a current evacuation pattern and different widths of protection cover (0.2 mm and 0.8 mm) have been produced, and their performance and stability were measured. The detection efficiency of a single-gap chamber for $\beta$-rays from a $^{90}$Sr source was measured to be up to approximately 60 % in both electrode samples. The target efficiency can be achieved even with a drop of 100 $-$ 150 V. On the other hand, after more than a dozen hours of operation, discharges suddenly occurred and the detector was prevented from further operation. These discharges created current paths on the spacing pillars. This serious problem must be investigated and solved in the future.