Studies on the features of characteristic resistance of a no-insulation superconducting coil in energizing and de-energizing processes

A coil wound with no-insulation (NI) winding technique can present enhanced electrical/thermal stability and more compact structure but poorer energizing/de-energizing instantaneity as compared to an insulated counterpart. The above features of a NI coil are resulted from its turn-to-turn contact resistance, namely, the characteristic resistance Rc. Rc is a rather important parameter of a NI coil, and it is greatly influenced by winding tension, more intrinsically, the compactness of coil winding pack. Alone with the winding tension, Ampere's force that is induced by coil current and magnetic flux density, may also apply on each turn of a NI coil to influence the compactness of coil winding pack, and further the Rc and electrical behaviors of the coil. This paper explores the aforementioned influences caused by Ampere's force through energizing and de-energizing tests. Experimental results show the Rc decreases as charging current increases. Meanwhile, simulation results indicate the Ampere's force applied on each coil turn has a compressive effect and the force is proportional to the square of charging current. Furthermore, a step-rising energizing method together with a modified circuit model are proposed to calculate instantaneous current-dependent Rc. And precise prediction of coil electrical behavior is acquired. Totally, the Ampere's force do have influence on coil electrical behavior especially when the operation current and flux density are large.