Generation of Periodic Magnetic Field Using Bulk MgB₂

The generation of strong periodic magnetic fields with short periodic lengths is very attractive for accelerator-based compact high-power future light sources. We have developed a new type of undulator using HTS bulk material to overcome the field strength limitation due to the maximum energy product (BH)(max) of permanent magnets and the engineering current density of superconducting wires. REBCO bulk is the most attractive material for realizing high-field undulators because of its extremely high J(c) at low temperatures. However, REBCO bulk requires a melt growth process with seed crystals to produce a single-domain superconducting bulk, and this process tends to introduce batch-to-batch variations in J(c). As a result, it is difficult to precisely control the peak-to-peak magnetic field fluctuations of the periodic magnetic field. Therefore, we focused on MgB2, which does not show weakly linked electromagnetic behavior, and thus does not require a melt growth process with seed crystals. In this study, we demonstrated for the first time in the world the generation of a periodic magnetic field using MgB2 bulk arrays and confirmed that the peak-to-peak fluctuations are smaller than those of REBCO bulk.