Intense, high brightness H- beams from surface plasma sources

High-current H^- beams from a reliable surface plasma source are of great interests for spallation neutron sources and hadron colliders. At Maryland, H^- beams have been studied using a magnetron and a Penning-type surface plasma source. Stable operating conditions with negligible beam noise have been achieved in both cases. The beam characteristics are much improved in the Penning geometry; the beam brightness is about an order of magnitude higher. An emission current density of ~1 A/cm² with normalized beam brightness of ≳10¹² A/(m-rad)² has been achieved. The minimum energy spread ΔE (FWHM) is measured ≲2.5 eV. The actual ΔE is possibly much smaller since this value is close to the resolution of the energy analyzer. The results are sensitive to the beam noise, and the gas pulse is the key control parameter here. Long, stable operations with very limited source maintenance have been noted. So far, an emission aperture of diameter=0.6 mm is used when the H^- beam current is ≳2 mA at 10 kV. The beam current can be scaled to ≳30 mA for an emission aperture of diameter ~2.4 mm. The critical issues for noiseless, high-brightness H^- beams, the source performance, and the scaling of beam parameters are discussed