H- beam neutralization measurements in a solenoidal beam transport system

H- beam space-charge neutralization is measured for 65-mA, 35-keV beams extracted from a circular-aperture Penning surface-plasma source, the small-angle source. The H- beam is transported to a RFQ matchpoint by a two-solenoid magnet system. Beam noise is typically ±4%. A four-grid analyzer is located in a magnetic-field-free region between the two solenoid magnets. H- beam potentials are deduced from kinetic energy measurements of particles (electrons and positive ions) ejected radially from the beam channel by using a gridded energy analyzer. Background neutral gas density is increased by the introduction of additional Xe and Ar gases, enabling the H- beam to become overneutralized