Coupling Current and AC Loss in LHC Superconducting Quadrupoles

One of the issues for the operation of the LHC accelerator at CERN are the field errors generated by coupling currents in the superconducting cables of the main dipoles and quadrupoles, especially during the initial phase of the energy ramp from injection conditions. Coupling current effects have already been measured in the superconducting dipoles, and results are reported elsewhere. This paper reports similar measurements that we have recently performed on different types of LHC superconducting quadrupoles (arc quadrupole, dispersion suppressor and matching section quadrupoles) to quantify the above effects and compare them to the values specified from the beam tolerances. Loss and field errors due to ramping are mainly determined by the contact resistance Rc between the strands of the magnets cables. In this paper the Rc is calculated for several quadrupoles measured using both the measured energy loss and the magnetic field errors during ramping of magnets.