Thermal study of the ironless inductive position sensors installed on the LHC collimators

The safe operation of the European Organization for Nuclear Research Large Hadron Collider relies on a complex system for equipment protection. An essential part of machine protection is the collimation system since it is used to protect the equipment from beam losses. This is achieved by using two jaws to intercept the particles making up the beam halo. Since the jaws are in close proximity to the beam, they must be positioned with micrometer precision from it. An ironless inductive position sensor (I2PS) is a relatively new linear position sensor used to measure the distance of the jaws with respect to the beam. During the operation, it is noted that the position read by the I2PS could be affected by temperature variation causing position-reading errors. This paper presents an experimental study conducted on the I2PS to determine the relationship between the position read by this transducer and the ambient temperature. Furthermore, this paper aims at determining the impact of the temperature changes in the collimator body, on which the I2PS is installed, and the position read by the sensor. The results show that the uneven thermal distribution along the body of the sensor leads to high position readings error. These results also show that, depending on the moving coil position, the sensor behaves differently, and hence, it is very difficult to compensate for the effect. Finally, this paper presents the results of a possible modification tested on the same setup to reduce the thermal effects.