  H- volume sources and, especially, caesiated H- volume sources are important
ion sources for generating high-intensity proton beams, which then in turn
generate large quantities of other particles. This chapter discusses the
physics and technology of the volume production and the caesium-enhanced
(surface) production of H- ions. Starting with Bacal's discovery of the H-
volume production, the chapter briefly recounts the development of some H-
sources, which capitalized on this process to significantly increase the
production of H- beams. Another significant increase was achieved in the 1990s
by adding caesiated surfaces to supplement the volume-produced ions with
surface-produced ions, as illustrated with other H- sources. Finally, the focus
turns to some of the experience gained when such a source was successfully
ramped up in H- output and in duty factor to support the generation of 1 MW
proton beams for the Spallation Neutron Source.
