Local Quality Control of Helical CORC Cable Winding

Thispaper discusses the possibilities of detecting defects in the helical winding of CORC cables using Hall probe scanning method and a 4-contact measurement method using a “magnetic knife”. The “magnetic knife” technique consists in a local change of the external magnetic field on the investigated part of the cable, which leads to a change in the current-voltage characteristic (I–V curve) of the entire cable. The presence of defects is determined by the appearance of features in the I--V characteristic when the “magnetic knife” moves along the cable. The Hall probe scanning method is sensitive only to the section of the cable located close to the scanning plane, which is not suitable for finding a defect in the coils. And is not suitable for the analysis of deep layers of the tapes, only the signal from the upper tape can be measured. The “magnetic knife” technique makes it possible to detect defects in tapes, the ab-plane of which is located at an angle of less than 45 degrees to the direction of the magnetic field (that is, the ab-plane is almost perpendicular to the direction of the field). We have shown that the technique is well sensitive to local defects, leading to a local decrease in the critical current by 3% of the whole cable. The developed technique is planned to be used to control the quality of winding and laying of CORC cable when creating an inductive energy storage for the NICA accelerator complex.