Author: Martino, M.
Paper Title Page
TUPS039 Reduction of Magnetic Interference on the Position Sensors of the LHC Collimators 1623
 
  • A. Masi, M. Lamberti, R. Losito, M. Martino
    CERN, Geneva, Switzerland
 
  The jaws of the LHC collimators have to be positioned with respect to the beam with an accuracy of 20 μm. On some collimators, installed in the LHC transfer lines from SPS, huge reading errors of several tens of micrometers have been observed on the Linear Variable Differential Transformer (LVDT) positioning sensors in synchronization with the variable magnetic field produced by the feed cables of the pulsed resistive dipoles of the transfer line. In this paper we introduce and describe in detail the problem, the model developed using FLUXTM for the simulation of the magnetic flux density generated by the current cables in the complex environment of an LHC transfer line, and the magnetic shielding we designed and implemented. Finally, we compare the results of simulations with experimental measurements taken during on-line pulsed magnets test campaigns.  
 
TUPS040 Driving the LHC Collimators' Stepping Motors over 1 km with High Accuracy avoiding EMI Effects 1626
 
  • A. Masi, G. Conte, R. Losito, M. Martino
    CERN, Geneva, Switzerland
 
  The LHC collimators are exposed to very high levels of radiation, which means that the power drivers must be installed far from the stepping motors that they drive. Due to the geometry of the underground installations, the distances can be up to 1 km. The long cables that connect the drivers to the motors behave as transmission lines modifying dramatically the impedance seen by the drivers and consequently jeopardizing the control performance of Pulse Width Modulation (PWM) drivers. In this paper we address this problem, provide an analytical model of the driver-cable-motor system and describe the analog solution we have developed to improve the performance of a typical off the shelf driver. Finally we characterize the improvement of the performances with measurements of positioning repeatability and show that electromagnetic emissions from the long cables are drastically reduced, making the use of stepping motors compatible with extremely sensitive instrumentation such as the LHC Beam Loss Monitors (BLM).