Pulsed-wire system for magnetic-field measurements on an in-vacuum undulator at NSRRC

Pulsed-wire measurement of a magnetic field has been developed by many groups. A pulsed-wire system has been set up and used to measure an in-vacuum undulator magnetic field at NSRRC. A copper zirconium wire (length 4 m, diameter 100 μm) has been selected. The pulse current is generated with an in-house power supply. A high-resolution and fast-feedback laser-photodiode system served to detect the displacement of the wire. Construction of an in-vacuum NdFeB-permanent-magnet undulator (period 22 mm, magnetic length 2 m) has been completed for Taiwan Photon Source. In this work, we applied a highly stiff, thin copper zirconium wire to diminish the maximum sag during measurement of a long undulator. We also demonstrate that the distance between the location of a wire dispersion sensor and a fixed point of the wire is an important issue to separate the main and weak reflection signals in pulsed-wire measurement. From the results of the undulator measurement, we obtained the magnetic field performed with the pulsed wire and Hall probe measurements, which are compared.