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Light-Ion Beam Focusing by z-Discharged Plasma Channel

Experimental and theoretical studies of proton-beam focusing by a z-discharged plasma channel that produces an azimuthal magnetic field are presented. The channel is produced in a Pyrex tube (50 mm in diameter, 140 mm in length) at a pressure of 0.2 Torr (air), which is fired by a fast capacitor bank (1.9 µF, 60 kV). A proton beam extracted from a flat-type, magnetically-insulated diode (850∼990 kV, 80 kA, 75 ns) is injected into the channel which is typically fired at voltage ∼32 kV and current ∼52 kA. Experimentally, we have observed the density enhancement at the focal point with a factor of (11∼15). Numerical calculation has also been carried out on trajectories of proton beams, assuming them only to be subject to Lorentz force. A reasonable agreement between the experiment and the theory is obtained on the focusing point or the enhancement factor of the density.