An electron gun for a sheet beam klystron

Summary form only given. Calabazas Creek Research, Inc. (CCR) is developing a rectangular, gridded, thermionic, dispenser-cathode gun for sheet beam devices. The first application is expected to be klystrons for advanced particle accelerators and colliders. The current generation of accelerators typically use klystrons with a cylindrical beam generated by a Pierce-type electron gun. As RF power is pushed to higher levels, space charge forces in the electron beam limit the amount of current that can be transmitted at a given voltage. The options are to increase the beam voltage leading to problems with X-Ray shielding and modulator and power supply design, or to develop new techniques for lowering the space charge forces in the electron beam. The current program addresses issues related to beam formation at the emitter surface, design and implementation of shadow and control grids in a rectangular geometry, and is directed toward a robust, cost-effective, and reliable mechanical design. A prototype device will be developed that will operate at 415 kV, 250 A for an 80 MW, X-Band, sheet-beam klystron being developed by Stanford Linear Accelerator Center. The cathode will have 100 cm/sup 2/ of cathode area with an average cathode current loading of 2.5 A/cm/sup 2/. For short pulse formation, the use of a grid was chosen. We will report the electrostatic and beam optics design in both 2- and 3-D as well as a thermal-mechanical analysis of the cathode region. The 2-D calculation gives the basis for the 3-D simulation, which, particularly with the grid structure, is expected to take a great deal of time per run. The modeling was done using Trak, a code from Field Precision. This code allows the use of variable mesh size, a feature that is essential for accurately including the grid structure. To minimize the power lost to the grid, the cathode has non-emitting segments in line with the grid. These segments are in the form of sections of arcs to help focus the beam around - he grid, which is formed of 1.25 mm, wire. With careful adjustment of this geometry and the grid potential, an emittance close to that of an ungridded gun can be achieved. At a beam current of 256A, the emittance was 7 10/sup -5/ /spl pi/ m rad.