PHOTON SCIENCE

Helmholtz coils are a pair of circular coils with radius R and arranged parallel to each other at distance S. In case R=S, the magnetic field in the centre of the two coils is uniform and field lines are parallel.

Helmholtz coils are used to characterize smaller individual magnet blocks which are later sorted based on this characterization and are ultimately assembled in the larger magnet arrays of an undulator or on smaller devices like phase shifters.

To measure the magnetization M of a block magnet, it is placed in the centre of the (unmagnetised) Helmholtz coils with its magnetization vector pointing along the direction of the coil axes. The block is then rotated by 180 deg and the induced voltage, V, is measured. M can then be derived from integration over V; R, S, and N, the number of windings.

Further literature: James A. Clarke: “The Science and Technology of Undulators and Wigglers”, Oxford University Press, 2004

Contact: P. Neumann, P. Vagin