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Description
A pulsed-wire system has been set up and used to measure an in-vacuum undulator magnetic field at NSRRC. A copper zirconium wire 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. The performance of magnetic fields is similar; the magnetic-field and pole-length errors peak to peak are both less than 1 %; the first and second integral fields are similar. The pulsed-wire system provides quick measurements of the magnetic field and is easy to install on any undulator.