To confirm a ferrite-core model for the superconducting rings (supertrons) to focus and guide electron current beams, we examined a bismuth-based ring into the configuration of which already sintered 1 μm sized 2223-phase powders were cold-isostatic pressed. No additional sintering was performed on the ring. Although the four-probe dc electric resistance of the ring increased with decreasing temperatures down to 77 K, the ring effectively shielded the self-magnetic field of single pulsed nanosecond-order electron currents (∼340 keV, ∼1 kA, ∼10 ns), below the Tc. These results certainly support the model, and provide a clue useful in applications of bulk superconductors.

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