Review and prospects of world-wide superconducting undulator development for synchrotrons and FELs

Abstract

Superconducting undulators (SCUs) with period >15 mm can offer much higher on-axis undulator field B0 than state-of-the-art cryogenic permanent magnet undulators (CPMUs) with the same period and vacuum gap. The commissioned NbTi planar SCUs for user operation in the Karlsruhe Institute of Technology (KIT) synchrotron and the Advanced Photon Source (APS) storage ring are operated stably without quenches, producing outperformed photon flux in the high energy part of the hard X-ray spectrum. Another potential advantage of deploying SCU is its radiation hardness, a crucial characteristic for being used in free electron lasers (FELs) driven by high repetition rate superconducting linear accelerators (LINACs) and diffraction limited storage rings (DLSRs) with small vacuum gap and large averaged beam current. Development of shorter period but high field SCU is an important mission in an EU founded CompactLight project as this technology would reduce both the length of undulators and the length of LINACs. This review paper first overviews the research and development of SCUs worldwide from late 1970s to 2021, then presents the SCU design requirements and compares the theory limits of different types of planar and helical SCUs, and finally reviews the technical challenges including the SCU cryostat, the magnetic field measurement, the integral/local field correction and the high-temperature superconductor (HTS) challenges and prospects the research needs for SCUs.

Design Study for HybriSCU: A HYBRID NbTi/ReBCO Superconducting Undulator

“…The latest results achieved a peak field on axis of 1.54 T at 10 K with a 4 mm magnetic gap, as reported in [10]. For a comprehensive review of the most recent tests on ReBCO-based undulators, the authors suggest referring to [11]. HybriSCU surpasses the performances of the NbTi-based SCU in terms of magnetic field on axis further enhancing its tunability range.…”

Superconducting undulators: permanent magnets after all

“…Nevertheless, with Nb-Ti SCUs, B 0 values above 1.5 T have been achieved, however with periodicities not below 15 mm. While PMUs are standard in storage rings to date and often serve as a reference, SCUs regained strong interest in the last two decades, also due to the development and improvement in high-temperature superconducting (HTS) wires and tapes and the possibility of avoiding liquid He temperatures [4]. Indeed, such high-temperature SCUs have been developed since 2014 in Los Alamos [5], Argonne [6], Seoul [7], Beijing [8], and Karlsruhe [9,10].…”

Novel correction procedure for compensating thermal contraction errors in the measurement of the magnetic field of superconducting undulator coils in a liquid helium cryostat

“…Research and development of superconducting undulator coils requires building up test stands for characterization of the coils (Mashkina et al, 2008;Harder et al, 2005;Grau et al, 2016;Kasa et al, 2019). Increasing stringent mechanical requirements on the coils' precision calls for development of high-precision diagnostics for their characterization (Zhang & Calvi, 2022). discussed how the European XFEL facility benefits from the ongoing research and development program on SCUs for possible future upgrade of the accelerator towards producing harder X-rays and improving the tunability of the beamline.…”