Evaluation of the Radiation Environment of the LHCb Experiment

The unprecedented radiation levels of the Large Hadron Collider (LHC) during high-energy proton-proton collisions will have an impact on the operation of its experiments’ detectors and electronics. LHCb, one of the 4 major LHC experiments, has started operation in 2009 and from 2011 onward it has been collecting data at and above its design luminosity. Detectors and associated detector electronics are prone to damage if the radiation levels exceed the expected values. It is essential to monitor the radiation environment of the experimental area and compare it with predictions obtained from simulation studies in order to assess the situation and take corrective action in case of need. Understanding the existing radiation environment will also provide important input to the planning of maintenance and for operation at upgrade luminosity. A set of radiation detectors has been installed in the LHCb experimental area to measure different aspects of its radiation environment. Passive dosimeters including Thermo-Luminescence-Dosimeters, Radio-Photoluminescence-Dosimeters and Polymer-Alanine-Dosimeters are distributed throughout the detector to cover the wide range of radiation levels expected. Many of these sensors, widely used for the measurements of radiation fields, are applied in the unprecedented radiation environment that is being produced in the experiment. Active radiation monitors, consisting of small printed-circuit-boards with multiple radiation sensitive field-effect-transistor and diode sensors have been installed close to passive sensor positions to allow for the monitoring of both peak and long term radiation levels. They can be read out online and the data stored in a database. The thesis involves studying the radiation environments of the experiment in all of its aspects. Measurements collected by the active and passive sensors are analyzed and converted from raw data to physical quantities. Cross calibrations are performed between the two systems and the measurements are correlated with the evolving running conditions. Another important element of the project is the comparison of the measurements with simulation estimates. Many aspects of the radiation environment of the LHCb experiment have been numerically evaluated in the past assuming 14 TeV center of mass (CM) collision energy and nominal LHCb luminosity. In order to better compare the expectation with the measurements, new simulation studies reflecting the run conditions in 2010-2013 with 7 and 8 TeV CM collision energy are performed. These simulation studies to evaluate the various aspects of the radiation environment of LHCb are carried out with FLUKA, a state of the art program for the simulation of high energy particle transport and interaction with matter. The results are reviewed, also in regard to integrating changes in the experimental setup if needed. Establishing the reliability of the simulation is essential, as it is needed to provide important input for technical choices in view of the planned upgrade of the experiment for operation at higher luminosity.