Low-mass x-pinch as a point-like source of MeV protons

Pulsed-power generators concentrate electrical energy in time and space, producing plasmas with extreme properties. During the final stage of current focusing, a current-carrying column can be compressed by its own magnetic field through the pinch effect. Among various pinch configurations, the x-pinch—formed by crossing two or more wires in an x-shape—has been extensively studied as a micrometer-scale, sub-nanosecond x-ray source. Here, we explore a novel aspect of x-pinches, highlighting their potential as a point-like source of MeV protons. The x-pinch experiments were performed on the XP generator, delivering a peak current of 500 kA with a rise time of 70 ns. A hybrid x-pinch configuration, comprising two solid conical electrodes connected by a single polymer fiber, was employed. A critical requirement for reproducible acceleration of protons to MeV energies was the use of low linear-mass fibers. Using nylon and polyethylene fibers with diameters of 25–40 μm, protons with energies of up to 3.9 MeV were observed in the radial direction, i.e., perpendicular to the fiber axis. Additional source parameters, particularly the effective source size and the anisotropy of the radial emission, were characterized using various CR-39-based ion detectors. Finally, the applicability of the x-pinch as a point-like proton source was demonstrated by x-pinch-driven proton radiography of an exploding wire.