Operational Experience and Improvements of the LHC Beam Current Transformers

During the 2010 run the LHC continuously improved its performance. In particular the bunch charge and number of bunches were significantly increased, which revealed certain limitations of the LHC beam current transformers. The DC current transformers (DCCT), used to measure the circulating beam current, exhibited saturation related to bunch intensity, the number of batches in the machine and their spacing. Two major issues were also discovered on the fast beam current transformers (FBCT) used to measure the individual bunch charges: discrepancies in the measured intensities when compared to the DCCTs measurements and a bunch length dependence on the measured intensity. Further analysis showed that both problems are linked to the beam position dependence of the signal acquired from the toroids used in the FBCTs. This paper presents the observed issues, discusses possible solutions and reports on the results from modification made for the 2011 run.