File:VFPt braunbek coil.svg

English: Magnetic field around a Braunbek coil[1] consisting of four round current loops with identical current, which are aligned around a common symmetry axis. This arrangement removes variations in the magnetic field, up to its 7th-order derivative with respect to the center, making it the smoothest possible field achievable with four circular coils of identical current.

The inner loops have an axial position ${\displaystyle z_{1}=\pm 0.27803\,R_{1}}$ and radius ${\displaystyle R_{1}}$. The outer loops have an axial position ${\displaystyle z_{2}=\pm 0.84566\,R_{1}}$ and radius ${\displaystyle R_{2}=0.76390\,R_{1}}$. The current through all loops is ${\displaystyle I}$. The central magnetic field is ${\displaystyle B_{0}=1.28861\mu _{0}I/R_{1}}$.

The dots symbolize where the current flows out of the image plane, whereas the crosses are where the current flows into the plane.