Design of the prototype low energy beam transport line for the Spallation Neutron Source

The design of the Spallation Neutron Source (SNS) prototype low-energy beam transport (LEBT) system is discussed. This LEBT must transfer 35 mA of H/sup $/current from the ion source outlet aperture to the entrance of the radio-frequency quadrupole (RFQ). The plasma generator is a radio-frequency-driven multicusp source, operated at 6% duty factor (1 ms, 60 Hz). The entire LEBT configuration is electrostatic, with a high-voltage extraction gap followed by two sets of Einzel lenses. The second Einzel lens will be split into four quadrants to permit the application of transverse steering and beam chopping fields. The H/sup -/ ion source emits a gas flow into the LEBT that must be efficiently pumped to reduce stripping losses of the H/sup -/ ions. Therefore, an efficient electrode design is incorporated to reduce the gas pressure between the electrodes. Alignment requirements and related issues will also be discussed.