托卡马克内部线圈套管导体偏心缺陷的涡流检测方法

Testing of Eccentricity in Tokamak In-vessel Coil Conductors

在托卡马克装置中,内部线圈(IVCs)为三层套管导体结构,内管为铜管,外管为Inconel/不锈钢合金管,两管之间采用陶瓷层提供辐射电阻,使内外管绝缘。在内部线圈的加工成型过程中,套管导体结构内部铜管有可能产生与外侧钢管不同轴,即偏心缺陷,导致中间陶瓷绝缘层厚度分布不均匀,降低整个内部线圈的性能。因此对套管导体是否发生偏心及偏心程度进行在线无损检测和评价非常重要。针对偏心检测,笔者提出了基于涡流检测的方法,并基于退化磁矢位Ar法对其有效性进行了有限元数值分析,探究了检测信号与偏心距离间的关联规律,同时通过初步试验,验证了其可行性。

The conductor of in-vessel coil （IVCs） in Tokamak is three-layer tubular structure. It consists of a water-cooled copper alloy as an inner tube surrounded by ceramic insulation and a stainless-steel alloy jacket tube. During manufacture of IVCs, eccentricity may occur between the copper tube and stainless-steel tube. It leads to thickness change in the insulation layer and may seriously influence the performance of the entire IVC. Therefore, it is crucial to detect and quantitatively evaluate the eccentricity via online non-destructive testing means. In this paper, an eddy current testing （ECT） based method is proposed to detect the eccentricity of IVC conductors. A finite element model for multi-frequency eddy current testing of IVC eccentricity is built based on the reduced magnetic vector potential method （Ar ） to investigate the dependence of the ECT signals on the tube eccentricity. In addition, a preliminary experiment is also conducted to check the feasibility of the proposed method for practical application.