Comparison between Powder-Pressed and Melt-Processed Bulk Superconductor Lenses (Supertrons) for Electron Beams

To confirm a model for operation of powder-pressed bulk superconductor lenses (Supertrons), Y-based quench-melt-growth (QMG) bulk superconductors were used to focus intense electron beams (340 keV, ∼ 1 kA, and 5∼ 10 ns). The lens focused the beams much less effectively than any of the Y-, Bi-, and Tl-based powder-pressed bulk lenses and even worse than a copper-made lens. These facts support the validity of the model in which powder-pressed bulk superconductors behave like ferrite cores at frequencies of some hundred MHz.