Profiles of Relativistic Electron Beams Focused with High-Temperature Superconducting Lenses (Supertrons)

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Abstract
Relativistic electron beams (REBs, 310 keV, 1.5 to 3.8 kA, pulse widths of about 5 ns) were focused with high-temperature Bi- and Y-compound, straight and tapered superconducting lenses (Supertrons, inner diameters of 5, 10, and 20 mm, thickness of 1.5 mm, and axial length of 40 mm) to diameters of 2 mm or less (full width at half maximum). The gently tapered Bi-compound lens showed the highest functioning in focusing REBs with current density of more than 400 A/mm2. Radial profiles of the REBs focused were visually confirmed with open-shutter photographs of fluorescence of neon gases excited by the REBs. A bent superconducting tube guided REBs as optical fibers do. To rate the focusing ability of these lenses, a figure of merit was proposed.