Dynamic performance of linear electromagnetic actuators in a stray magnetic field: theoretical analysis and experimental verification

Abstract

Linear electromagnetic actuators (LEAs) are widely used in tokamaks, but they are extremely sensitive to and are prone to fail in high-strength stray magnetic field (SMF) which is usually a concomitant with tokamaks. In this paper, a multi-physics coupling analysis model of LEA including magnetic field, electric circuit and mechanical motion is proposed, and the dynamic characteristics of LEA in SMF are studied in detail based on the proposed model. The failure mechanism of LEA in SMF is revealed, and the influence of SMF on the dynamic performance of LEA is studied and quantified. It is shown that, the failure threshold of the LEA selected in this work under the rated condition is 27 mT and 14 mT in the positive and negative direction, respectively. Under a typical SMF of 10 mT in the negative direction, the closing time of the LEA will be extended 40%, while its opening time will be shortened about 10%. Experimental tests are also conducted, which verify the validity of the proposed model and the analysis results. This paper provides a basis for the diamagnetic optimization design of LEA, and it is of great significance to ensure the reliable operation of tokamak.

Fusion power supply advances by the J-TEXT engineering team

“…Increasing the driving voltage can improve the immunity of the piston-type LEA against an SMF, but it will also increase the driving power, and may lead to a severe bounce. As the effect of the SMF gets weaker when the armature moves towards the contact point, a voltage-doubling circuit based on a pre-charged capacitor is proposed in [20]. The increased driving voltage ensures the successful action of the LEA under an SMF at the initial stage.…”

“…We proposed the optimization design method of the magnetic field generating coil [16], which is the key component of the test platform, and designed the test coils for J-TEXT and ITER, and also helped the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) to complete the design of the test platform [17,18]. In addition, the exploration of the failure of electromagnetic actuators [19,20], which are the most sensitive to SMF, and their optimization [21] is briefly introduced.…”