Speaker
Description
The University of Bergen is involved in the design and development of the Electromagnetic Forward Calorimeter (FOCAL-E). This is a major upgrade for LHC Run 4 to the ALICE experiment at CERN. This paper presents the power board design for FOCAL-E pixel layers that provides power to the ALPIDE sensor strings connected to a transition card. The design comprises radiation-hard bPOL48V modules attached to a cold plate. The power board controls AVDD, DVDD and PVDD for the ALPIDE strings, it monitors the bus voltage and current, and it reads the detector layer temperature sensors through a readout unit FPGA.
Summary (500 words)
The Forward Calorimeter (FOCAL) upgrade is one of the two major detector upgrades of the ALICE experiment for LHC Run 4. FOCAL consists of an Electromagnetic Calorimeter (FOCAL E), followed by a Hadron Calorimeter (FOCAL H). The FOCAL E comprises 22 modules, with 11 modules installed on each side of the beam pipe. Each module is segmented into 20 sampling layers, two of which are high granularity pixel layers. The pixel layers are composed of six individual strings, each containing 15 ALPIDE pixel sensors. The ALPIDE sensor was originally developed for the ALICE Inner Tracking System upgrade (ITS2) for LHC Run 3.
The pixel readout electronics is based on the ITS2 architecture, which has been successfully operated during Run 3. It includes an FPGA based readout unit (RU) that controls a dedicated power board (PB). In contrast to ITS2, the FOCAL design introduces a transition card (TC), which is directly connected to the pixel layer. The TC forwards data to the RU and receives a power supply of +6 V from the PB. The ALPIDE strings require stable +1.9 V supplies for the AVDD, DVDD, and PVDD voltage rails, as well as an adjustable back bias voltage between 0 and −5 V. To fulfil these requirements, the TC hosts radiation tolerant bPOL12V DC DC converters that regulate the +6 V input voltage to +1.9 V. This solution ensures stable power delivery up to the maximum expected Total Ionizing Dose of 600 kRad at the TC location. The PB provides individual enable lines for each ALPIDE string, allowing rapid power down of individual strings if required.
As in ITS2, the FOCAL pixel RU incorporates two FPGAs: an AMD Xilinx Kintex UltraScale SRAM based FPGA and a radiation tolerant flash based Microchip IGLOO2 FPGA. The IGLOO2 is used to control and monitor voltages and currents supplied from the PB to the TC, as well as to read out detector layer temperatures via PT100 sensors.
Two detector configurations are implemented for the FOCAL E pixel layers: an outer barrel (OB) configuration and a combined inner/outer barrel (IB/OB) configuration. In the OB configuration, three TCs are powered by a single PB, while in the IB/OB configuration each PB supplies one TC. This scheme follows the RU architecture, resulting in a total of 28 RUs and 28 PBs for the FOCAL E pixel system.
The PB is equipped with radiation hard bPOL48V buck modules that convert the input voltage +16 V provided by CAEN to +6 V for the TC. The bPOL48V modules are attached to a custom designed cold plate shared between the PB and the RU. This cold plate efficiently removes the heat dissipation of approximately 5 W per converter.
The power board prototype has successfully passed the internal review process and is scheduled for production in April 2026, with mass production expected by the end of the year. This contribution presents the technical design of the PB, along with results from laboratory testing and operational experience.