Upper Limits of Electron Beam Currents Focusable with High-T c Bulk Superconductor Lenses (Supertrons)

A tapered Bi-based high- T c bulk superconductor tube was used as a lens (Supertron) for relativistic electron beams (REBs). When REBs (340 keV, ∼1 kA, ∼10-ns pulse width) were injected into a lens with a 3-mm-diameter exit, the REBs were quenched at ∼440 A. These results, in addition to those from previous papers, reveal possible upper limits of the electron beam currents to be focused; the compressed self-magnetic field of the electron beams should be less than ∼600 G at the inner surface of the lens exit. A model was proposed for the operation of Supertrons.