Screening Currents Within the EuCARD HTS Dipole

The EuCARD high temperature superconductor (HTS) insert is a dipole magnet generating a self-field of 5.4 T and designed to operate at 18 T within the FRESCA2 test facility; it has just been successfully tested in stand-alone configuration up to 4.5 T (see M. Durante et al.). To operate in such a large field, its winding is made of a 12 mm HTS REBCO insulated conductor; each conductor is composed of four tapes in parallel to achieve a large current of 2.8 kA. The drawbacks of using parallel HTS tapes are numerous: first, they are very sensitive to orthogonal field inducing screening currents loops within the tapes. Second, the use of tapes in parallel imposes to transpose the conductor to avoid current loops between tapes, induced from the parallel field. The screening currents in return generate a magnetic field (screening current induced field), opposed to the main one and consequently lowering it and degrading the homogeneity. We have developed a finite difference code in order to simulate the induced currents within a conductor made of parallel tapes; we have calculated the screening current induced field and showed that the order of magnitude is non negligible compared to the main field. These computations have been benchmarked against measurement of the magnetic field performed during the stand-alone configuration tests.