Compression and propagation of an intense ion beam in a strong magnetic field

An intense pulsed ion beam (≳50 keV, ∼80 A/cm², and ∼400 ns pulse length) from a magnetically insulated ion diode was injected axially into a strong magnetic field (up to 2.2 T). This long pulse, high-density proton beam was efficiently guided and compressed (2r=6.0 cm to 2r≲2.0 cm) by the magnetic field. The current density at the center of a beam under a maximum magnetic field (40 cm from the diode) was increased by a factor of 4 (up to 320 A/cm²). The beam radius, calculated by the snow-plow model, indicated that a more effective compression could be obtained by a strong magnetic field under ideal conditions. The observed large beam radius, compared with the radius expected from the model, could be attributed mainly to field penetration into the beam radius since the skin depth of the ion beam (c/ω_p ∼0.4 cm) was not much smaller than the radius of the initial beam (r₀ ∼3 cm). By applying a magnetic field that was greater than 0.8 T, the ion beam was propagated 50 cm without loss.