Magnetic Field Measurement of BEPC II Superconduction Magnets by Using Rotating Coil

Superconducting interaction region (IR) magnets for Beijing Electron Positron Collider Upgrade Project (BEPC II) are used for increasing the BEPC II luminosity, correcting close orbit and coupling. These magnets are placed as close as possible to the interaction point (IP), immersed within the BES III detector solenoid field of 1.0 T. These magnets are designed into two magnet packages at each side of the IP with each contained inside a magnet cryostat.Each superconducting magnet package includes several function magnets of SCQ, SCB/HDC, VDC, SKQ and AS. Some of them, such as SCQ, SCB/HDC, VDC, SKQ were measured by rotating coil, and the integrals field and high order harmonic contents, local field along the beam line are known in details. Comparing these results with that from BNL which were measured inside the vertical Dewar, it's found that there were only small differences. Comparing with the results from the stretched wire, for SCQ and SCB as examples, it's found that the differences for the main fields are less than 3 x 10-3. As a result, the method presented in the paper can be used for absolute magnetic field measurements. (authors)