Multicharged boron ions from pure elements evaporated in a 2.45-GHz ECR source

Abstract

Multicharged boron ions have been produced by vaporizing pure boron powder in a 2.45-GHz electron cyclotron resonance (ECR) ion source. A vapor source is boron-nitride crucible with a tantalum heater and radiation shields, and set in an ECR plasma along the geometrical axis of the mirror field. The opening of the crucible faces an ellipsoidal ECR zone formed at the bottom of the magnetic mirror trap. The vapor pressure of boron covers the range of the experimental pressure (10/sup -4//spl sim/10/sup -3/ Pa) with the crucible temperature of about 1500/spl deg/C. Insertion of the vapor source scarcely affects charge state distributions in the ECR plasma, while inserting a dc-biased target into the ECR plasma seriously deteriorated them. Production efficiency of multicharged boron ions have been improved much more than that in the experiments by sputtering boride target. The boron flux into the ECR zone Is evaluated in both cases of evaporation and sputtering. It is considered that this enhanced production results from the energy reduction of the neutral boron particles.