Magnetic field around a three-loop Barker coil[1] consisting of three 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 5th-order derivative with respect to the center.The inner loop is placed around the center and carries the current 0.531463I{\displaystyle 0.531463\,I}. The outer loops have an axial position z=±0.760051R{\displaystyle z=\pm 0.760051\,R} and current I{\displaystyle I}. The central magnetic field is B0=0.770361μ0I/R{\displaystyle B_{0}=0.770361\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