Numerical methods for the magneto-mechanical coupling analysis of invessel components in Tokamak devices

Magneto-mechanical coupling vibration arises in the in-vessel components of Tokamak devices especially during the plasma disruption. Strong electromagnetic forces cause the structures to vibrate while the motion in turn changes the distribution of the electromagnetic field. To ensure the Tokamak devices operating in a designed state, numerical analysis on the coupling vibration is of great importance. This paper introduces two numerical methods for the magneto-mechanical coupling problems. The coupling term of velocity and magnetic flux density is manipulated in both Eulerian and Lagrangian description, which brings much simplification in numerical implementation. Corresponding numerical codes have been developed and applied to the dynamic simulation of a test module in J-TEXT and the vacuum vessel of HL-2M during plasma disruptions. The results reveal the evident influence of the magnetic stiffness and magnetic damping effects on the vibration behavior of the in-vessel structures. Finally, to deal with the halo current injection problem, a numerical scheme is described and validated which can simulate the distribution of the halo current without complicated manipulations.

Caution to Apply Magnetic Barkhausen Noise Method to Nondestructive Evaluation of Plastic Deformation in Some Ferromagnetic Materials

Magnetic Barkhausen Noise(MBN) method is known as an effective nondestructive evaluation(NDE) method for evaluation of residual stress in ferromagnetic materials. Some studies on the feasibility of the MBN method for NDE of residual strains were also conducted and found applicable. However, these studies are mainly focused on the state of residual strains which were introduced through a one-cycle-loading process. In practice, however, structures may suffer from an unpredictable and complicated loading history, i.e., the final state of plastic strain may be induced by several times of large loads. Whether the loading history has influences on MBN signals or not is of great importance for the practical application of the MBN method. In this paper, several ferromagnetic specimens with the same final state of residual strain but of different loading history were fabricated and inspected by using a MBN testing system. The experimental results reveal that the loading history has a significant influence on the detected MBN signals especially for a residual strain in range less than 1%, which doubts the feasibility to apply the MBN method simply in the practical environment. In addition, micro-observations on the magnetic domain structures of the plastic damaged specimens were also carried out to clarify the influence mechanism of loading history on the MBN signals.