Coupling Current and AC Loss in LHC Superconducting Quadrupoles

Abstract

Abstract-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 R c between the strands of the magnets cables. In this paper the R c is calculated for several quadrupoles measured using both the measured energy loss and the magnetic field errors during ramping of magnets.Index Terms-Author, please supply your own keywords or send a blank e-mail to keywords@ieee.org to receive a list of suggested keywords.

Effects of Core Type, Placement, and Width on the Estimated Interstrand Coupling Properties of QXF-Type Nb₃Sn Rutherford Cables

“…Accordingly the 10 A/s b3, for example, at the injection field of 0.54 T was only 0.053 units compared to an expected 0.46. Likewise high values of Rc have been obtained in measurements of LHC quadrupoles [16].…”

“…Coupling currents generating by the ramping-up of current in LHC dipoles and quadrupoles produce small increases, B1 and B2 (~0.05 mT), in the main fields, B0. Normalized to B0 these increases ("field advances", FA) are represented by the "units" b1 and b2, 1 unit being equal to 10 at CERN of FA, cn, and energy (AC) loss in current-ramped LHC dipoles and quadrupoles [14][15] [16].…”

“…Field Advance: Measurements of FA (for both apertures) were performed on a string of eight main quadrupoles at current ramp rates of 10-50 A/s [16]. The average FA was 1.0-2.4 units, much smaller than the 15 units associated with the target quadrupole Rc of 20 μΩ.…”

“…Multipoles: Rotating-coil measurements of multipole amplitudes were made on seven main quadrupoles (both apertures) [16]. The average value of b3 (reference radius 17 mm, I = 760 A, dI/dt = 10 A/s) was 0.206 units and the deduced average Rc was 135 μΩ.…”

Magnetic measurement of interstrand contact resistance and persistent-current magnetization of Nb3Sn Rutherford cables with cores of MgO tape and woven S-glass ribbon

“…Both coupling currents and persistent currents produce cable magnetization components that distort the bore fields of accelerator dipoles and quadrupoles [1]. Thus in order to achieve tight control of the particle beam during injection, acceleration, and storage it is necessary to minimize these field distortions.…”