Helium-Free Field Measurement System for Superconducting Undulator Coils

Superconducting undulators generate, for a given period length and a given gap, higher fields than permanent magnet undulators. Since in an undulator the photons add up coherently over the whole undulator length, even small magnetic field errors can disturb the superposition of photons and reduce the intensity of the generated photon beam. Therefore, as in any other undulator, the magnetic field has to be measured with high accuracy.