LHCb - The Design and Construction of the LHCb VELO modules

The construction of the new LHCb Vertex Locator (VELO) detector is presented. The upgraded subsystem will play a crucial role in the tracking during data-taking runs starting in 2021, its main objective locating primary and secondary vertices. Compared to its predecessor, the main advantages are better resolution together with trigger-less readout at the maximal rate of 40 MHz. In total, VELO consists of 52 modules positioned in vacuum along the LHC beampipe, surrounding the interaction point. The modules are populated with 4 hybrid silicon pixel detectors with pixel pitch of 55 $\mu$m. Each of the sensors is read out by 3 VeloPix ASICs with 256x256 pixels. For experiment control and data propagation, sets of front-end hybrids and GBTx ASICs are utilized. The data are then sent through a vacuum feed-through board to an opto-and-power (OPB) board, which is connected to the rest of the experiment via optical fibres. Cooling of the whole module is achieved by phase transition of liquid CO2 using a custom-made silicon micro-channel substrate. The assembly of modules at both University of Manchester (Manchester, UK) and Nikhef (Amsterdam, NL) requires high precision in many aspects, therefore extensive procedures for the large-scale construction and its quality assurance have been deployed. The information during each step is uploaded to the online database and automatically analyzed, providing instantaneous information about quality of both components, performed tasks and whole modules. Final assembly of the whole system then takes place at University of Liverpool (Liverpool, UK) and is then transported to CERN (Geneva, CH).