Test of superconductivity of pick-up coils for STEP accelerometer and their modification

To ensure the fully superconductivity of a 3D superconducting film in the range of working current required by an accelerometer in the STEP mission and to realize the acceleration measurement in an accuracy of 10^-18g, the cryo superconductivity of pick-up coils was tested by several experiments. Tested results show that there are uperconductivity failures in the 3D film coils. A subsection method was used to test the 2D composition of the 3D film coils separately, by which the locations of superconductivity failures were determined and the reasons why the failures were happened were obtained. Finally, the method to improve the coil design was presented. After modification according to the method, the film coils have turned to be fully superconducting and their allowable superconducting currents are demarcated from -40 mA to 40 mA. With a 300% margin, they satisfy the requirement of the STEP mission for the working current range from -10 mA to 10 mA. Through the test, analysis and modification, the design and manufacture of pick-up coils are finalized, which lays the technical foundation for STEP mission, and completes engineering applications of 3-D superconducting film coils.