Self-Focusing Of A High Current Density Ion Beam Extracted With Concave Electrodes In A Low Energy Region Around 150 Ev

Spontaneous self-focusing of ion beam with high current density (J(c) similar to 2 mA/cm(2), I-b similar to 65 mA) in low energy region (similar to 150 eV) is observed in a hydrogen ion beam extracted from an ordinary bucket type ion source with three electrodes having concave shape (acceleration, deceleration, and grounded electrodes). The focusing appears abruptly in the beam energy region over similar to 135-150 eV, and the J(c) jumps up from 0.7 to 2 mA/cm(2). Simultaneously a strong electron flow also appears in the beam region. The electron flow has almost the same current density. Probably these electrons compensate the ion space charge and suppress the beam divergence. (C) 2013 AIP Publishing LLC.