Magnetization measurements on LHC superconducting strands

Abstract

When using superconducting magnets in particle accelerators like the LHC, persistent currents in the superconductor often determine the field quality at injection, where the magnetic field is low. This paper describes magnetization measurements made on LHC cable strands at the Technical University of Vienna and the Institute of Physics of the Polish Academy of Sciences in collaboration with CERN. Measurements were performed at T=2K and T=4.2K on more than 50 strands of 7 different manufacturers with NbTi filament diameter between 5 and 7 micrometer. Two different measurement set-ups were used: vibrating sample magnetometer, with a sample length of about 8mm, and an integrating coil magnetometer, with sample length of about 1m. The two methods were compared by measuring the same sample. Low field evidence of proximity effect is discussed. Statistics like ratio of the width of the magnetization loop at 4.2K and 2K, and the initial slope dM/dB after cooldown are presented. Decrease of the magnetization with time, of the order of 2% per hour, was observed in some samples. Abstract When using superconducting magnets in particle accelerators like the LHC, persistent currents in the superconductor often determine the field quality at injection, where the magnetic field is low. This paper describes magnetization measurements made on LHC cable strands at the Technical University of Vienna and the Institute of Physics of the Polish Academy of Sciences in collaboration with CERN. Measurements were performed at T=2K and T=4.2K on more than 50 strands of 7 different manufacturers with NbTi filament diameter between 5 and 7 micrometer. Two different measurement set-ups were used: vibrating sample magnetometer, with a sample length of about 8mm, and an integrating coil magnetometer, with sample length of about 1m. The two methods were compared by measuring the same sample. Low field evidence of proximity effect is discussed. Statistics like ratio of the width of the magnetization loop at 4.2K and 2K, and the initial slope dM/dB after cooldown are presented. Decrease of the magnetization with time, of the order of 2% per hour, was observed in some samples.

Passive correction of the persistent current effect in Nb/sub 3/Sn accelerator magnets

“…According to [8], at the compensation field of 1 T, the NbTi strand magnetization is T. For the same strand packing factor, core magnetization and width as in the considered Nb Sn cable, the core thickness should be 0.6-0.9% of the cable thickness or 10-15 m for 1.8 mm thick cable, which is safe for the coil winding.…”

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

“…From the results of M-B-loop measurements of an LHC-inner strand measured at 2 K [10] the shielding magnetization at 0.54 T adjusted to that at 1.9 K using Bottura's scaling relationship [11] turned out to be 10.58 kA/m. Alternatively, using Equation (3) kA/m in very good agreement with the directly measured value.…”

The Development of Superconducting Magnets for Use in Particle Accelerators: From the Tevatron to the LHC

“…To monitor this effect, the magnetization of the strands was measured. An hysteresis cycle up to 1 T is performed, and the width of the loop at 0.5 T has to meet specification (30 and 23 mT for the outer and inner layer respectively) within 4.5% [46]. In order to meet this goal strands with extreme values of magnetization were sorted during cabling.…”