Design, Construction and Magnetic Measurements of the HU640 (OPHELIE2) Undulator dedicated to the DESIRS VUV Beamline at SOLEIL

A novel electromagnetic Insertion Device (ID) called HU640 (OPHELIE2) has been developed and constructed for the DESIRS beam line at SOLEIL. It is a 10 m‐long helical/planar undulator designed to produce any kind of switchable photon polarizations in the range 5 eV – 40 eV. It is composed of three sets of pure air coils mounted in a special arrangment. One set coils is dedicated to generate the horizontal field component. Two other sets, shifted the one from the other by a quarter of period along the ID axis, produce the vertical component with a continuous translation dephasing varying from −180° to +180°. The use of non magnetic material makes the undulator linear with the coil current in terms of peak field and residual integrated field errors. This allows the number of magnetic controls, corrections to be significantly reduced and to ease the on‐beam operation. The paper presents the design, the construction and the magnetic measurements of the undulator.