High current density negative ion source for beam line transport studies

The Fermilab Electron Cooling Program requires a 20 m solenoidal region to interact 8-GeV antiprotons with an escorting beam of 4.3-MeV electrons to improve the phase-space quality of the antiproton beam. The solenoidal section with additional transport lines to take and return a 0.5-A electron beam from an electrostatic accelerator, for energy recovery, must be precisely aligned and adjusted. For the initial setup and study, and later testing of this line, a 12.4-keV H^- beam can be used to simulate the 4.3 MeV electron beam. For this purpose a high-brightness H^- ion source has been developed and tested. The source, a semiplanatron type, with a hollow cathode discharge and spherical cathode focusing of the emitted ions to the emission aperture has given an emission current density up to 0.7 A/cm². Continuous operation of 4 weeks has been demonstrated. Such an optimized source could have many applications for tandem accelerators, ion beam lithography and ion implantation