A novel powering scheme based on DC-DC conversion for the luminosity upgrades of the CMS tracking system at CERN

摘要

The instantaneous luminosity of the LHC is expected to reach 2 x 10^{34} s^{-1} cm^{-2} and 5 x 10^{34} s^{-1} cm^{-2} around the years 2019 and 2024, respectively. After the second upgrade the LHC will be referred to as the High Luminosity LHC (HL-LHC). In order to benefit from the higher luminosities, CMS foresees to upgrade its pixel detector during an extended winter shutdown of the LHC at the end of 2016 and the beginning of 2017. During a long shutdown of the LHC over the years 2022 and 2023, it is foreseen to install a completely new tracking system in CMS. Both upgrades are expected to result in the need to provide more electric current to the detector. However, power losses in cables already contribute 50 % to the power consumption of the present tracker and rise with the current squared. Since no more space is available for cables, and thicker cables within the tracking volume spoil the material budget of the detector, new powering schemes are considered mandatory. CMS foresees the use of radiation tolerant DC-DC converters on the front-end to reduce power losses on cables. This thesis describes the new powering scheme of the CMS pixel detector and discusses the options with respect to a new strip tracker. A radiation and magnetic field tolerant DC-DC converter prototype, the PIX_V8A, is introduced and the research that led to its development is summarised. The PIX_V8A has been developed for the application in the pixel upgrade and is also a first approach for a DC-DC converter for the later upgrade of the CMS tracking system. The PIX_V8A makes use of the AMIS4 chip, which has been proven to stay operational for total ionising doses of up to 1 MGy and fluences of up to 10^{15} n_{eq} cm^{-2}. With an input voltage of 10 V, the PIX_V8A converter provides an efficiency of about 80 % for output voltages of 2.5 V and 3.0 V. Within this thesis the robustness of the novel powering scheme and the qualification of the PIX_V8A are demonstrated in several tests, including system test measurements with silicon strip detector modules and silicon pixel detector modules in combination with an evaporative CO2 cooling system.