Ion beam extraction with ion space-charge compensation in beam-plasma type ion source

Abstract

The beam-plasma type ion source that we have developed has an original ion- beam extraction mechanism. An ion beam is formed with an ion space-charge compensation by electrons which are distributed by force in the extraction region. The electrons are used in order to ameliorate an ion space-charge effect, which might be an obstacle for high-current ion-beam extraction. The space charge of ions is effectively neutralized by many kinds of energetic electrons; that is, a primary electron beam, a secondary electron beam, and high-energy plasma electrons. When the ion space-charge compensation by these electrons is effective, theoretically, the divergence of an ion beam is suppressed, the space-charge limitation of an extractable ion current is relaxed, and the shape of the ion-emission surface is improved. Therefore, a high-current ion beam with good quality can be extracted, even at a low-extraction voltage. In the experiment, the current of more than 0.1 A at the extraction voltage of 1–5 kV, which was more than ten times the normal space-charge limited current, was extracted from a single aperture under the ion space-charge compensation condition.