High-Energy Protons from X-pinch Plasmas: First Observation and Application to Proton Radiography

Pulsed power facilities concentrate electrical energy in time and space to produce plasmas with extreme properties. In the final stage of energy focusing, a current-carrying column is compressed by its own magnetic field via 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 [1]. This presentation reveals a novel aspect of the x-pinch: its potential as a point-like source of MeV proton beams.

Ion emission from x-pinches has been investigated on the XP generator (Cornell University) and MAIZE (University of Michigan) at 400 kA currents with 70 and 200 ns rise times, respectively. Most of the experiments were performed in a hybrid x-pinch configuration, involving solid conical electrodes connected by a single fiber. A critical requirement for reproducible MeV proton beam generation was the use of low linear-mass fibers. Using 30 μm-diameter polyethylene fibers, protons with energies up to 3.3 MeV and an estimated (virtual) source size of 200 μm were observed. Protons up to 6 MeV were also detected from low-mass metallic wires, such as 17 μm aluminum. The fast protons were emitted during gap formation following fiber disintegration. Protons were observed in the radial direction, perpendicular to the fiber axis. Acceleration mechanisms in z-pinches have so far been associated with the axial direction toward the cathode [2]. This work therefore provides new insights into ion acceleration mechanisms in current-carrying plasma columns and demonstrates the potential of an x-pinch-driven proton source as a novel platform for the study of pulsed-power plasmas [3].

[1] Pikuz, et al., Plasma Phys Rep. 41 (2015) 291.

[2] Klir, et al. New J. Phys. 20 (2018) 053064.

[3] Munzar, et al. Plasma Phys. Control. Fusion 66 (2024) 075021.