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. 2016 Nov 29:6:37937.
doi: 10.1038/srep37937.

Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets

Teruhiko Bizen  1 , Ryota Kinjo  2 , Teruaki Hasegawa  2 , Akihiro Kagamihata  1 , Yuichiro Kida  2 , Takamitsu Seike  1 , Takahiro Watanabe  1 , Toru Hara  2 , Toshiro Itoga  1 , Yoshihiro Asano  2 , Takashi Tanaka  2
Affiliations

Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets

Teruhiko Bizen et al. Sci Rep. .

Abstract

We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

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Figures

Figure 1
Figure 1. Results of the flux-loss measurement in the SACLA undulators.
Each figure shows the peak-field variation at each magnet pole as a function of the distance from the entrance. Measured data over the whole undulator length are shown in (a), while details near the entrance are shown in (b) and (c).
Figure 2
Figure 2
Summary of the flux-loss measurement; (a) the maximum flux loss and (b) evaluated phase error are plotted as a function of the segment number.
Figure 3
Figure 3. Schematic drawing of the magnetic array of the SACLA undulator.
Dimensions are in mm.
Figure 4
Figure 4
Contour plots of Bz near the surface of the PM; (a) measured for the PM extracted from the entrance of the SACLA undulator (1st segment), (b) computed with the assumption that the area surrounded by the dashed line is initialized by the electron bombardment, and (c) measured for the PM irradiated with the electron beam in the synchrotron.
Figure 5
Figure 5. Results of irradiation experiments.
The observed flux loss is normalized and plotted as a function of the number of incident electrons Ne.
Figure 6
Figure 6. Spatial distribution of the the reverse field in the three conditions (i)~(iii).
Figure 7
Figure 7
Consideration of the reverse field in the three conditions (i)~(iii): (a) simplified configurations of the MR regions, and (b) the averaged reverse field formula image plotted as a function of Sr.
See this image and copyright information in PMC

References

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