Beam optics for ion extraction with a high-voltage-ratio acceleration-deceleration systems

The current of ions which can be extracted from a plasma source across a single gap is limited at low extraction voltages by restrictions set by the value of the beam perveance. A possible method of overcoming this limitation is to use a two-stage extraction system, in which ions are accelerated to a voltage V 1 and then decelerated to the required voltage V 2 (V 2 >V 1 ). The beam optics of this two-stage extraction system are analysed using a simple multiple-lens model.