Enhanced production of multicharged boron ions by approaching a boride target to an ECR zone

Multicharged boron ions have been produced by a sputtering boride target in a 2.45-GHz electron cyclotron resonance (ECR) source. The target material is immersed in an ECR argon plasma along the geometrical axis of the mirror field, and dc bias voltages are applied. Extracted boron ion currents increase as the target approaches the ECR zone formed at the bottom of mirror trap although the argon charge state deteriorates. The increase of boron ion current is coincident with that of the solid angle subtended by the target at the ECR zone. Measurement of the boron flux shows that the increase of boron atoms sputtered into the ECR zone causes this enhanced production. Ratio of total boron to argon ion current and that of B2+ to B+ current are about 10% and 10%endash 20%, respectively. The B3+ current can be detected at low microwave power (∼150 W). The isotopes of boron are clearly separated in natural abundance ratio. copyright 1996 American Institute of Physics