NSRRC Activity Report 2022

Facility Development and Status 097 was approximately 1%. The largest differences were observed at the first four and last four poles. The magnetic field can be obtained through differentiation of the first integral field. Figure 6(a) presents the measurement results obtained using the pulsed wire and Hall probe systems. With the first four and last four poles are ignored, the standard deviation of the peak field was 7379 ± 19 G for the Hall probe measurement and 7363 ± 43 G for the pulsed wire measurement. The length of each pole can be obtained for comparing the period lengths. The average pole lengths obtained through the pulsed wire and Hall probe measurements were 10.9995 and 10.9990 mm, respectively, for a difference of less than 1%, as shown in Fig. 6(b) . In the pulsed wire magnetic field measurement, the peak-to-peak variation was less than 1%, which is similar to that obtained through the Hall probe measurement ( Figs. 7(a) and 7(b) ). The electron beam in a storage ring has a finite energy spread; small changes in field errors do not affect the spectral properties of undulator radiation. Figure 7(c) presents the difference in the peak magnetic fields obtained through the two measurement systems. For the second integral measurement, we adjusted the current pulse width to 20 ms. The second integral field was obtained using Eq. (2). Figure 8 shows the pulsed wire and Hall probe measurements of the second integral field. For the Hall probe measurement, the second integral field was obtained through numerical integration of the first integral field. The second integral field measurements obtained through the two systems were similar. Summary A pulsed wire measurement system was developed and used to measure the magnetic field of an in-vacuum undulator. Pulsed wire and Hall probe measurements for a 2-m undulator were compared. We obtained the magnetic field strength through simple numerical differentiation of the pulsed wire measurement. The magnetic field measurements were similar; the errors in the peak-to-peak magnetic field and pole length were both less than 1%, and the first and second integral field measurements were similar. The pulsed wire system offers rapid magnetic field measurement and is easy to install on any undulator. The pulsed wire measurements were similar to those obtained using the Hall probe system. In the future, the pulsed wire system can be used to measure the magnetic fields of undulators with small gaps. (Reported by Chih-Wei Chen) Fig. 7 : Pulsed wire and Hall probe magnetic field measurements: (a,b) peak- to-peak variation; (c) difference in peak magnetic fields. Fig. 8 : Pulsed wire and Hall probe, second integral field measurements.