Magnetic field around a Barker coil[1] consisting of four round current loops with identical radius R{\displaystyle R} aligned along a cylinder. Distances and currents are optimized to remove variations in the central magnetic field, up to its 7th-order derivative with respect to the center.The inner loops have an axial position z1=±0.243186R{\displaystyle z_{1}=\pm 0.243186\,R} and current 0.442391I{\displaystyle 0.442391\,I}. The outer loops have an axial position z2=±0.940733R{\displaystyle z_{2}=\pm 0.940733\,R} and current I{\displaystyle I}. The central magnetic field is B0=0.792263μ0I/R{\displaystyle B_{0}=0.792263\mu _{0}I/R}.
The dots symbolize where the current flows out of the image plane, whereas the crosses are where the current flows into the plane.
Own work
Geek3