Magnetic Field Mapping in the BESIII Solenoid

The Beijing Spectrometer III (BESIII) superconducting solenoid magnet, which is running in the Beijing Electron Positron Collider II (BEPC-II), is an important part of BESIII and provides a 1 Tesla field in the main drift chamber. A 3-D mapping device with three 3-D probes was fabricated to measure the field components of $B_{z}$ , $B_{r}$ and $B_{\mit\Phi}$ . The mapping of the magnetic field of the BESIII superconducting solenoid magnet is presented, with the accelerator interaction region magnets located inside the BESIII solenoid excited to different current values. A set of polynomials, and a few trigonometric-Bessel terms are used to fit the data. The measurements and the functional model agree to 5 Gauss within the main drift chamber tracking volume at nominal field values.