Beam intensity measurements in the Large Hadron Collider

The number of particles in the particle beam, commonly referred to as beam intensity, is a crucial parameter for safe and efficient operation of any particle accelerator. The Large Hadron Collider (LHC) is equipped with current transformers which measure the electric current of the beam used to derive the beam intensity. There are two types of current transformers installed in the LHC. The DC Current Transformers (DCCTs) measure direct current signals whereas the bandwidth of the Fast Beam Current Transformers (FBCTs) ranges from a few hundred hertz to over a gigahertz. Throughout the run of the LHC, the FBCTs' readings were observed not to be fully independent of beam position and bunch length which imposes important limitations. To address these limitations a prototype of an Integrating Current Transformer (ICT) has been developed at CERN. In this paper, its design, principle of operation along with results of first beam tests are presented. The paper describes also the measures taken to install and test the prototype with LHC beams. The measured beam-position-dependency of the ICT has been improved, compared to the FBCT, by factors 35 and 50 in the vertical and horizontal planes, respectively.