Contact mechanical characteristics of Nb₃Sn strands under transverse electromagnetic loads in the CICC cross-section

Abstract

This paper presents a new code for the two-dimensional discrete element method (DEM) and relevant simulations to quantitatively characterize the contact force behavior of the Nb 3 Sn strands in the ITER CICC cross-section under a transverse electromagnetic load. In order to obtain the essential parameters in the contact force model employed in the DEM, a simulation of the experiments conducted by Nijhuis et al (2004 IEEE Trans. Appl. Supercond. 14 1489 is first performed, where the load-displacement curve predicted by the code is in good agreement with the measurements. After that, the contact force chain between strands and its distribution is quantitatively analyzed by the code. It is found that the contact force distribution among strands is heterogeneous and strongly anisotropic. In other words, the force chain distribution, which determines the behavior of the assembly of strands with discrete media, and the distribution of area average magnitude of the contact force are obviously inhomogeneous. To describe this inhomogeneity, here, the probability density function (PDF) is used in the statistical analysis. The numerical results show that the PDFs of the magnitudes of the resultant contact force, normal contact force, and tangential contact force all decay with an exponential law, and that PDFs of the directions of the contact forces are all anisotropic and exhibit about six periodic changes in which the peak values in the direction parallel to the applied electromagnetic load are appreciably larger than the other peaks.

Numerical investigation on transverse heat transfer properties in cross section of full size Nb3Sn CICC ITER conductor

“…20 And then, the multi-stage of the strands in the cable can be realized by connecting the strands with equivalent springs and the interactions among strands can be described by friction-contact model. Furthermore, the central spiral, cable wrap and petal wraps are considered.…”

“…[20][21][22] The reader can also refer to the detailed descriptions of the multistage physical model of the Nb 3 Sn CICC conductor in our earlier publication. 20 Traditionally most believe that the CICC cables are mainly cooled by the convective heat transfer from strand to liquid helium, the heat transfer in liquid helium between the annular region and central spiral. [14][15][16] In this work, the contact heat transfer among strands is taken into consideration.…”

“…), which was described in our earlier publication. 20 Based on this model, more cyclic transverse load-displacement curves were obtained. 21 The results indicate that the microscopic contact features among strands play an important role in determining the macroscopic mechanical properties of the cable.…”

“…Based upon the established discrete dynamic model for multistage Nb 3 Sn CICC conductor cross section, 20 the contact heat transfer among strands and convective heat transfer in liquid helium are introduced in this work. The time-temperature curves of cable during cooling process are systematically analyzed firstly.…”

Analytic calculation of magnetic force between two current-carrying coils

“…Current-carrying coils are basic elements for constructing electromagnetic magnet systems such as linear actuators and motors [1][2] , or even higher field magnets from high temperature superconductor wires or tapes [3][4][5] , for example, the magnetic resonance imaging (MRI) [6] or nuclear magnetic resonance (NMR) [7] magnet, and the international thermonuclear exprimental reactor (ITER) magnet system [8][9][10] . For the design and safety operation [11] of these magnet systems with current-carrying coils, it is important to accurately calculate the magnetic field of a current-carrying coil and the magnetic force between two coils.…”