Extraction of a nearly monoenergetic ion beam using a pulsed plasma

A nearly monoenergetic ion beam was extracted from a capacitively coupled pulsed Ar plasma. The electron temperature decayed rapidly in the afterglow, resulting in uniform plasma potential, and minimal energy spread for ions extracted in the afterglow. Ion energy was controlled by a dc bias on a ring electrode surrounding the plasma. Langmuir probe measurements indicated that this bias simply raised the plasma potential without heating the electrons in the afterglow. A rejection grid downstream of the plasma allowed ions to pass only during a selected time window in the afterglow. The energy spread was 3.4 eV full width at half maximum for a peak ion beam energy of 102.0 eV. This energy spread is about an order of magnitude narrower than the beam extracted from the continuous plasma.