Low emittance immersed and non-immersed foilless diodes for high current electron linacs

A low-emittance immersed foilless diode injector was designed and built for the upgraded RADLAC-II (Radial Line Accelerator II) accelerator. The design is for a 5-MV, 40-kA annular beam with a 9-mm outer radius. A conical cathode field shaper eliminates the previously observed large cathode shank losses. In addition, the nonimmersed foilless diode approach was utilized in the design of the Sandia recirculating linear accelerator (RLA) injector. Low-energy (~1.7-MV) and high-energy (4-MV) designs were carried out in conjunction with a solenoidal vacuum beam transport and injection system. J.M. Creedon´s (1977) model formalism, the JASON code, and the new version of the MAGIC PIC (particle-in-cell) code that includes the slant geometry package were extensively utilized for the immersed diode injector design. The design of the nonimmersed diode and beam transport system is simpler, and only JASON and the trajectory code TRAJ were necessary to simulate this diode. The new RADLAC-II injector has been installed and very successfully operated. It met and in many instances exceeded all of the design goals