Observation of Radially Emitted Proton Beams from Low-Mass X-Pinch Plasmas.

Ion acceleration in Z-pinch plasmas is traditionally linked to the axial direction of current. Here, we report the radial emission of MeV protons from a low-mass, hydrogen-containing X pinch. Proton energies up to 3 MeV are observed in a hybrid X pinch with a 30  μm polyethylene fiber at a 400 kA peak current. The low-mass load, correlation of protons with hard x-rays, and timing of hard x-ray emission point to proton acceleration driven by current disruption following fiber disintegration. A new insight into the acceleration mechanism arises from the use of an interelectrode gap that is too short for magnetic fields to bend axially accelerated protons by π/2 radians; thus, the observed radial emission implies a substantial radial acceleration component. The radial emission also enables X-pinch-driven proton radiography, the exceptional potential of which is demonstrated with exploding wires.