Powerful cw proton linear accelerators (100 mA at 0.5–1.0 GeV) are being proposed for spallation neutron-source applications. A 75-keV, 110-mA dc proton injector using a microwave ion source is being tested for these applications. It has achieved 80-keV, 110-mA hydrogen-ion-beam operation. Video and dc beam-current toroid diagnostics are operational, and an EPICS control system is also operational on the 75-keV injector. A technical base development program has also been carried out on a 50-keV injector obtained from Chalk River Laboratories, and it includes low-energy beam transport studies, ion source lifetime tests, and proton-fraction enhancement studies. Technical base results and the present status of the 75-keV injector will be presented.

Simple analysis of the nearly Maxwellian angular distributions of the ribbon H− ion beams extracted from a long, narrow slit on the 8X source yields the H− temperature, kTH−. The derived kTH− are 0.1–0.3 eV for a 2-A dc discharge and 0.7–1.3 eV for a 400-A pulsed discharge. Because this diagnostic method relies on simple electronic techniques, it allows rapid study of the dependences of kTH− on the source parameters, such as gas flow and discharge current. These variations of kTH− in the 8X source are qualitatively similar to those observed for the H-atom temperature, kTH0, in the 4X source, another Penning surface-plasma source.

H− ion beams are extracted at 5–25 kV from a long, narrow slit on a Penning surface-plasma source (the 8X source). The extraction geometry produces negligible transverse electric fields (focusing effects) along the slit length. Therefore, the ion angular spread reflects the distribution of ion energies at the plasma surface. The angular distributions are measured with an electric-sweep emittance scanner whose slits are oriented normal to the long dimension of the emission slit. The nearly Maxwellian angular distributions measured over the central portions of the ribbon beam give kTH− of 0.1–0.2 eV for a 2-A dc discharge and 0.8–1.0 eV for 350–500 A pulsed discharges. This diagnostic technique has sufficient position resolution to allow measurement of the kTH− spatial distributions. It also allows study of the kTH− dependencies on ion source parameters (e.g., increasing the H2 gas flow lowers kTH−).

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