Design Considerations for High-Intensity Negative Ion Sources

The production of negative hydrogen ions (H-) by an ion source similar to that employed in many cyclotrons has been studied. The negative ions are extracted directly from the arc plasma in a direction normal to the magnetic field without use of a charge-exchange medium. In an attempt to improve the negative-ion yield, the arc-discharge chamber has been modified to conform to assumptions made as to the probable formation mechanism of the observed negative ions. Outputs of negative hydrogen ions in ex cess of 5 mA have been obtained. Ion-source operating parameters are discussed, as well as considerations for the utilization of this discharge geometry by negative-ion cyclotrons.