Improvements of the pulsed-wire method to measure undulators

We present the Pulsed-Wire Method (PWM) for undulator measurements used for the first crossed overlapped electromagnetic undulator OPHeLIE. This method gives directly the first integral of the magnetic field using a short current pulse and the second integral using a step current pulse through the wire. We characterized OPHeLIE using the second integral mode to optimize the beam trajectory in the respect of specifications. There was a good correlation between these results and those obtained from the on-beam test. We were therefore encouraged to further develop this method to determine optical performances of undulators. In order to validate this approach we compared the spectrum determined by the pulsed-wire technique and Hall probe scans, used as reference, applied both to the OPHeLIE prototype, which is a shorter planar version. For the PWM, we used the short current pulse according to the undulator's period (the first integral mode). Digital data processing techniques have been used to improve the signal-to-noise ratio, to minimize the effect of the background vibrations and to characterize the wire response.