A SIMPLE POSITIVE NEGATIVE SURFACE-IONIZATION SOURCE

A versatile, spherical-geometry, self-extraction surface ionization source has been designed, fabricated, and characterized. The source utilizes direct-surface ionization to form either positive or negative ion beams resulting from interactions between highly electropositive or electronegative atoms or molecules and a spherical-sector surface ionizer maintained at approximately 1100-degrees-C. For positive ion generation, the surface ionizer is chosen to be a high-work-function metal such as Mo, Ta, or W; while for negative ion formation, a LaB6 surface ionizer is selected. The design features and performance of the source for each of these modes of operation are discussed in this report.