Speaker
Description
One of the solutions proposed for the start time and reaction plane determination in the CBM experiment is the Beam Fragmentation T0 Counter. This detector will be located at the forward region where the particle fluxes are expected to reach 2.5x105cm−2s−1. Therefore, ceramic RPCs with floating electrodes of low bulk resistivity will be used due to their high rate capabilities. A single RPC cell consists of double-gap stacks, where the outer electrodes are high resistive Al2O3 ceramics with a Chromium layer deposited on them and the floating electrodes are made of low resistive Si3N4/SiC ceramics. A complete module is formed by three such cells (2x2cm2 or 5x5cm2) forming a six-gap RPC. The edge zones of the electrodes are grooved with a Rogowski cross section. This effectively reduces the dark current of the detectors and allows to operate them with higher electric field strengths. The usage of Isobutane free gas mixtures is mandatory for a long detector lifetime. A couple of modules were assembled and exposed with relativistic electrons at ELBE (HZDR) where a beam flux of up to 1.5x105 cm-2 s-1 was used, and with pions at the T10 beam-line (CERN). In both tests a detection efficiency of 98% was achieved. The next steps will be the commissioning and investigation of a multi-module prototype.
