Abstract
Further development of synchrotron light sources and new concepts for free electron lasers require undulators with short periods and high magnetic fields. A promising approach is the cryogenic permanent magnet undulator concept based on an advanced magnet material. This new rare earth alloy $(\mathrm{Pr},\mathrm{Nd}{)}_{2}{\mathrm{Fe}}_{14}B$, shows an increasing remanent field of up to 1.7 T without the limits of spin reorientation transition. This work presents first spectral measurements of a prototype cryogenic permanent magnet undulator, consisting of 20 periods of 9 mm in length, cooled by a closed cycle cryo-cooler to temperatures below 30 K. The $K$ parameter of 0.837 at RT is increased by more than 15% to 0.966, and an increase of the third harmonics photon flux of up to 66% was achieved. A possible degradation of the on-axis field quality due to thermally induced magnetic field errors, deduced from the measured bandwidth of the spectrum, is below the limits of the detector resolution of 2%.
Highlights
An advanced understanding of Nature’s fundamental structure and processes requires electromagnetic radiation with a short wavelength and pulse duration
Recent case studies [1,2] have shown that undulators with short periods offer advantages for different kinds of synchrotron light sources and free electron laser (FEL) schemes when they provide sufficiently high magnetic fields
The following measurements were done at RT, 294 K, and below 30 K in order to compare the performance of the new magnet material and to detect possible magnetic field errors generated by mechanical distortions due to the temperature drop
Summary
An advanced understanding of Nature’s fundamental structure and processes requires electromagnetic radiation with a short wavelength and pulse duration. Recent case studies [1,2] have shown that undulators with short periods offer advantages for different kinds of synchrotron light sources and free electron laser (FEL) schemes when they provide sufficiently high magnetic fields. Using these highfield short-period undulators, existing synchrotron light source facilities can extend their achievable photon energy range to the hard X-ray regime. Even state-of-the-art SC-materials (NbTi, Nb3Sn) require temperatures around 4 K to enable critical current densities above 1000 A=mm2 Associated with this are high costs for the cooling infrastructure due to a high heat load at temperatures where commercially available cryo-coolers are inefficient and expensive.
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