Speaker
Description
Summary
The ALICE (A Large Ion Collider Experiment) EMCal (Electromagnetic Calorimeter) readout electronics is a multi-channel data acquisition system. The detector signals are digitized in the Front-end Electronics (FEE) cards. The readout concentrator reads out data from the FEE cards and sends them to the ALICE DAQ (Data Acquisition) system. The bus network architecture is used in the current readout electronics. Because the bandwidth utilization efficiency of the communication bus between the FEE cards and the readout concentrator is lower than 25%. The maximum event readout rate of the EMCal is limited to about 3.3 kHz. This is much lower than the current ALICE Pb-Pb interaction rate of 8 kHz. In order to increase the event readout rate, the point-to-point link and the star network architecture are considered to be used in the new EMCal readout electronics.
There are some challenges on developing the new EMCal readout electronics. Since the EMCal is one of the sub-detectors in the ALICE experiment, the EMCal readout electronics should be compatible with the existing ALICE online systems (DAQ, DCS and Trigger systems). In addition, there are more than 500 FEE cards on the EMCal. Replacing all FEE cards almost equals to replacing the entire readout electronics on the EMCal. So, the new EMCal readout electronics should be also compatible with the current FEE cards. In addition, the new readout electronics should be flexible for the possible upgrade in the future.
Therefore, a specific adapter card has been carefully designed for the FEE card. It provides a point-to-point link between the FEE card and the new readout concentrator. The data, triggers, clock and commands are all transferred over this link. A Scalable Readout Unit (SRU, a new readout concentrator) has also been designed. The SRU hardware is universal and compatible with the current ALICE online system. All the communication protocols are realized by the FPGA on the SRU board. It is flexible for the future upgrade. The strategies used for reducing the dead time in the readout chain will be presented. The optimal performance and potential bottleneck of the new readout electronics are analyzed via simulation. The event readout rate of new readout electronics could be higher than the current readout electronics at a factor of six. When the EMCal event size is larger than 40% of the un-suppressed event data, the bandwidth of the ALICE DDL (Detector Data Link) between the SRU and the ALICE DAQ will become the bottleneck in the readout chain. The prototype of the new EMCal readout electronics has been tested in the lab. It will be installed on one EMCal super module soon. The correlation of the readout rate and the event size will be measured. The latest test results will be presented.