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A 10 mm-period, high-temperature superconducting (HTS) undulator consisting of 20 staggered-array GdBa2Cu3O7−x (GdBCO) bulk superconductors has been fabricated and tested successfully. Each GdBCO disk was machined into a half-moon shape with micro-meter accuracy and shrink-fitted into a slotted oxygen-free copper disk which provided pre-stress and effective conduction-cooling. The HTS undulator prototype, consisting of GdBCO disks, copper disks, and CoFe poles fitted in a long copper shell, was field-cooled magnetized in fields of up to 10 T at 10 K. An undulator field of 2.1 T in a 4 mm magnetic gap was obtained. This field is the largest reported yet for the same gap and period length and exceeds the target value of 2 T for the meter-long HTS undulator scheduled for the hard x-ray I-TOMCAT beamline in the Swiss Light Source 2.0. We have demonstrated that bulk superconductor based undulators can provide significantly improved performance over alternative technologies., Superconductor Science and Technology, 36 (5), ISSN:0953-2048, ISSN:1361-6668

A backward computation method has been developed to accelerate modelling of the critical state magnetization current in a staggered-array bulk high-temperature superconducting (HTS) undulator. The key concept is as follows: i) a large magnetization current is first generated on the surface of the HTS bulks after rapid field-cooling (FC) magnetization; ii) the magnetization current then relaxes inwards step-by-step obeying the critical state model; iii) after tens of backward iterations the magnetization current reaches a steady state. The simulation results show excellent agreement with the H-formulation method for both the electromagnetic and electromagnetic-mechanical coupled analyses, but with significantly faster computation speed. Solving the FEA model with 1.8 million degrees of freedom (DOFs), the backward computation method takes less than 1.4 hours, an order of magnitude or higher faster than other state-of-the-art numerical methods. Finally, the models are used to investigate the influence of the mechanical stress on the distribution of the critical state magnetization current and the undulator field along the central axis., 12 pages, 7 figures

The development of a new hard x-ray beamline I-TOMCAT equipped with a 1-meter-long short-period bulk high-temperature superconductor undulator (BHTSU) has been scheduled for the upgrade of the Swiss Light Source (SLS 2.0) at the Paul Scherrer Institute (PSI). The very hard x-ray source generated by the BHTSU will increase the brilliance at the beamline by over one order of magnitude in comparison to other state-of-the-art undulator technologies and allow experiments to be carried out with photon energies in excess of 60 keV. One of the key challenges for designing a 1-meter-long (100 periods) BHTSU is the large-scale simulation of the magnetization currents inside 200 staggered-array bulk superconductors. A feasible approach to simplify the electromagnetic model is to retain five periods from both ends of the 1-meter-long BHTSU, reducing the number of degrees of freedom (DOFs) to the scale of millions. In this paper, the theory of the recently-proposed 2D A-V formulation-based backward computation method is extended to calculate the critical state magnetization currents in the ten-period staggered-array BHTSU in 3D. The simulation results of the magnetization currents and the associated undulator field along the electron beam axis are compared with the well-known 3D H-formulation and the highly efficient 3D H-{\phi} formulation method, all methods showing excellent agreement with each other as well as with experimental results. The mixed H-{\phi} formulation avoids computing the eddy currents in the air subdomain and is significantly faster than the full H-formulation method, but is slower in comparison to the A-V formulation-based backward computation. Finally, the fastest and the most efficient A-V formulation in ANSYS 2020R1 Academic is adopted to optimize the integrals of the undulator field along the electron beam axis by optimizing the sizes of the end bulks., Comment: 19 pages, 12 figures