Electron controlled transport of intense neutralized ion beams

Experimental results are reported for an extended transport channel for long pulse, intense, neutralized ion beams. The transport channel is defined by neutralizing electrons confined by a weak solenoidal magnetic field (ion transit time << 2πω/sub ci/). Charge separation sheaths which occur when ions expand beyond the confined electron channel reflect the ions. Electrons which diffuse out of the transport region are removed by electrostatic fields. A 10 μs, 28 keV, .17 A beam of singly charged carbon ions is used to investigate the properties of the transport channel. With modest magnetic fields (< 100 G), the ion current incident on a collector .75 m from the ion source is increased a factor of 2.5 over vacuum transport levels. The addition of a small transverse magnetic field, ≤ 5 G, decreases the transported ion current. The reduction in current is consistent with the magnetic transport channel model. The scaling of transported ion current with magnetic field strength and sweeping bias is examined. Transport systems of this type may have direct application to both the low velocity initial stages and the high current final focussing region of accelerator inertial fusion drivers