Electromagneto-mechanical model of high temperature superconductor insert magnets in ultra high magnetic fields

Second-Generation High Temperature Superconducting (2G HTS) tapes are considered to be the main candidates for the development of future ultra high DC magnetic field magnets. In such application, the usability of the HTS magnets can be strongly impaired by large screening currents developed in the flat strip of the tapes. These currents lead to the generation of a Screening Current Induced Field (SCIF) that can deteriorate the performance by affecting the stability and the homogeneity of the magnetic field. Besides the SCIF, there is also the likely mechanical degradation of the tapes under the action of large Lorentz forces. The mechanical degradation and the presence of large screening currents intertwine to affect the reliable operation of 2G HTS magnets. To study those combined issues, an electromagneto-mechanical model based on tensile mechanical characterization of short samples was built to simulate the coupled electromagnetic and mechanical behaviour of insert magnets made of 2G HTS tapes under very high magnetic field. The coupling is carried out by considering the dependence of the n index and the critical current density Jc on the local relative deformation in addition to the magnetic flux density. The case study is the Little Big Coil (LBC, version 3) which broke the world record of the strongest continuous magnetic field achieved to this date. An analysis of the electromagneto-mechanical behavior of the LBC is conducted on the basis of information extracted from literature to show that the proposed model can assess the current magnitude at which the insert magnet quenched. Additionally, it is shown that the model can also provide some insights on the impact of the mechanical degradation of the tape on the SCIF hysteresis loop. The studies are conducted on the original LBC and on versions that include additional modifications such as harnessing and co- winding with rigid metallic tapes. These modifications are employed to limit the mechanical degradation of the HTS insert magnet under ultra high magnetic field. They are expected to deliver extra safety margin to 2G HTS insert magnets.

Flow behavior of cementitious-like suspension with nano-Fe3O4 particles under external magnetic field

The flow behavior of cementitious-like (limestone powder) suspension containing nano-Fe3O4 particles at constant shear rate of 10 s−1, characterized by the evolution of apparent viscosity over time, is investigated under various magnetic fields. Results show that the limestone powder suspension at flow-state exhibits remarkable magneto-rheological responses, reflected by a significant increase in the apparent viscosity after applying an external magnetic field. A higher field strength corresponds to a more rapid and pronounced response. The apparent viscosity experiences a sudden alteration with the stepwise change of the magnetic field due to the formation or disintegration of magnetic clusters. Linearly increasing magnetic field strength at low ranges (e.g. 0 T–0.3 T) shows less influences on the evolution of apparent viscosity, while at relatively high magnetic field, the apparent viscosity gradually increases with the magnetic field strength and the increase rate is comparable to that obtained under constant high magnetic field of 0.75 T. When the magnetic field is removed, the apparent viscosity exhibits a sharp reduction. If the magnetic field strength linearly decreases to zero, however, the apparent viscosity continuously increases until reaching a peak and then gradually decreases. This research shows in different ways how a desired apparent viscosity level of a cementitious-like suspension can be reached by means of an external magnetic field.