Multi-anode photon-multiplier readout electronics for the LHCb ring imaging Cherenkov detectors

A readout system for the Ring Imaging CHerenkov (RICH) detectors of the LHCb experiment has been developed. Two detector technologies for the measurement of Cherenkov photons are considered, the Multi-Anode Photo-Multiplier Tube (MAPMT) and the Hybrid Photon Detector (HPD), both of which meet the RICH requirements. The properties of the MAPMT are evaluated using a controlled single-photon source; a pixel-to-pixel gain variation of ~3 and a typical signal to noise of ~20 is measured. The relative tube efficiency is found to be reduced by ~26 % due to the detailed focusing structure of the MAPMT device. A radiation hard application-specific integrated circuit (ASIC) chip, the Beetle1.2MA0, has been developed to capture and store signals from a pair of MAPMTs. The Beetle1.2MA0 is built on the architecture of the Beetle family that was designed for silicon strip detectors, the difference being a modified front-end amplifier. The 128 input-channels of the Beetle1.2MA0 have a charge-sensitive pre-amplifier followed by a CR-RC pulse shaper, which is sampled into an analogue memory with a depth of up to 160 time slots at 40 MHz. The internal bias generator module of the Beetle has also been developed and tested. This module generates all the required voltage and currents required internally to the chip, and consists of voltage DACs, current DACs, a current-source and a voltage source. Beetle1.2MA0 evaluation chips were fabricated, and the performance when connected to a MAPMT is demonstrated in terms of pulse profile, noise, pulse spillover and overshoot. The Beetle1.2MA0 ASIC is found to be well suited to LHCb RICH readout requirements. A demonstrator system of the RICH readout electronics has been developed, which will serve either HPD or, with some small adaptation, MAPMT applications. Multimode fibres driven by vertical cavity surface emitting lasers (VCSEL) devices are used to transmit eventblocks of data in 900ns from the on-detector (Level_0 region) to the Level_1 region, which is located off-detector in a non-radiation environment. The data words are captured into 9-Mbit Quad Data Rate (QDR) static RAM at a rate of up to 160 MHz. The scheme for Level_1 data receipt and buffering is described, and results from a full system test are presented.