Cryogen—Free Setup for Local and Integral Magnetic Field Measurements of Superconducting Undulator Coils

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. Precise measurements of the magnetic properties of conventional, i.e., permanent magnet based insertion devices (IDs) has undergone huge improvements over the past years and initiated a new era in synchrotron light sources worldwide. A similar breakthrough is now necessary in the field of superconducting insertion devices. Therefore, a part of our R&D program for superconducting insertion devices is to perform quality assessment of their magnetic field properties. In this contribution we describe the equipment to perform magnetic measurements of the local field and of the field integrals of superconducting undulator coils up to 2 m length in a cold in vacuum (cryogen free) environment with a focus on the results of the factory acceptance test.