A high-precision position measurement instrument for particle accelerator collimators

An innovative high-precision digital instrument for position measurement of particle accelerators collimators is proposed. The instrument relies on Linear Variable Differential Transformers by exploiting the three-parameter sine fit to estimate the amplitudes of their secondary signals. Moreover, the crucial problem of interfering magnetic fields is analyzed by means of two different models: analytical, aimed at capturing the main physics of the phenomenon, and predictive, based on Finite Elements Method, for assessing the interference effects accurately. Both the models were validated by means of simulations and experimental tests. They provided a sound basis for defining design guidelines to an application-independent solution of the interference problem. The experimental validation of the models included the development of a measurement method and a measurement system for the general characterization of external magnetic fields as influence quantities for the position measurement by means of Linear Variable Differential Transformers. Different prototypes were also built and characterized in laboratory. Preliminary on-field results, gathered during Large Hadron Collider commissioning and operations at the European Organization for Nuclear Research (CERN), confirming the laboratory results and discussed. Therefore, the instrument was qualified as complying with the demanding requirements of Large Hadron Collider at CERN and is currently integrated in its collimators control system.