This monograph has evolved from the author’s research work on the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The SNS is the world’s most powerful accelerator-driven, short-pulse neutron scattering facility for scientific research and industrial development. It consists of a powerful proton accelerator, a liquid mercury target, and neutron scattering instruments. The SNS currently holds the world record for proton beam power for spallation sources, 860 kW, and is expected to achieve the design power of 1.4 MW by the summer of 2010. The SNS accelerator complex consists of a 2.5 MeV H? beam injector that includes a high-brightness H? ion source and a radio frequency quadrupole, a high-power linear accelerator (linac) of up to 1 GeV energy with a pulse length of 1 ms at 60 Hz, and an accumulator ring to compress the long linac pulses into short ones of about 700 ns with 1.5E14 protons per pulse.