Thesis Report number CERN-THESIS-2019-217 Title Measurement of the LHC beam profile using the Beam Gas Vertex detector Author(s) Wurkner, Benedikt (Vienna, Tech. U.) Publication 106 p. Thesis note PhD : Vienna, Tech. U. : 2019 Thesis supervisor(s) Schwanda, Christoph ; Zamantzas, Christos ; Vlachos, Sotirios Note Presented 20 Nov 2019 Subject category Accelerators and Storage Rings Accelerator/Facility, Experiment CERN LHC Abstract The Beam Gas Vertex (BGV) demonstrator was developed for the Large Hadron Collider (LHC) to demonstrate the feasibility of a beam profile measurement device using a tracking detector to reconstruct beam-gas interactions. It has been successfully installed on beam 2 in 2015. If the evaluation of the concept using the demonstrator is successful, the design will be optimized, manufactured and installed on both beams for the HL-LHC upgrade that will be performed between 2024 and 2026. My main contributions to the BGV project were the analysis of data taken by the detector, optimization of the reconstruction algorithm based on this data, the development and qualification of the beam size measurement algorithms, the alignment of the detector as well as the development of adequate monitoring. As a first step the applicability of the usage of beam-gas interactions for beam size measurements was shown. The results showed that the assumed number of tracks per interaction detected by the setup was too low to apply vertexing as the method of measuring the beam size. Thus the correlation method was used to calculate the beam size and all the properties of the BGV were qualified using this method. It could be shown, that the achievable precision of the BGV depends on the number of events acquired down to a limit of a few $\mu$m. Futhermore I was able to measure many different kinds of beams allowing for the characterization of the BGV in changing conditions. It has been shown, that the BGV is capable of performing bunch by bunch measurements as well as averaged results with the limit for the number of bunches that can be acquired at the same time currently determined by the available computing capacity. As a final step the results acquired with the BGV were compared to other beam size measurement devices already installed in the LHC.