Power and Monitor Solution for the Proton Computed Tomography Project

Abstract

The ProtonCT project is an academic endeavor carried out by the University of Bergen in collaboration with several universities and entities across the world. The end goal of the project is to improve dosage plans by directly measuring the relative stopping power of protons using a digital tracking calorimeter. Directly measuring relative stopping power as opposed to approximating it using CT numbers can provide a more accurate dosage plan. The digital tracking calorimeter will be able to do computed tomography scans of head-sized objects. The digital tracking calorimeter will utilize pixel detector sensors developed by CERN for the ALICE project. 43 pixel arrays, segmented into layers, measure the angle and energy of proton particles traversing through the layers. With 108 chips per layer, 4644 ALPIDE chips build up all the layers. At full load, the expected power draw is close to 2.5kW. This thesis explores the design of a user-controllable power delivery and monitoring system. Each layer consists of 12 ALPIDE strings, with 9 ALPIDE chips making up one string. A power delivery system capable of supplying one layer is realized by using a small form factor switch mode power supply unit. An FPGA design created by peer students connects the 43 power delivery systems to a graphical interface. A filter, monitor, and control solution is designed with a newly released AVR microcontroller unit. A custom PCB, named the Monitor Board, is designed to host the filter and the MCU with all its support circuitry. Using differential signaling, the 43 monitorboards communicate with a Xilinx Kintex UltraScale FPGA responsible for storing and relaying information over IPbus to the user. Each monitor board can switch the strings of its designated layer on or off. Diagnostics and soft startups/shutdowns can be executed through software. The back-biasing of an entire layer is customizable by using the microcontroller DAC and an onboard negative voltage supply. A temperature monitoring solution is designed with the use of a PT1000 element mounted close to the ALPIDE chips.