George V. Miram

Diagnostic techniques with a computer controlled beam analyzer

The beam analyzer is a very useful tool for evaluation of beams from electron guns. Due to advances in computers and automation, modern beam analyzers are extremely versatile, accurate, fast and precise. Rapid graphic presentation of test data in a three-dimensional format allows the engineer to routinely test for uniformity of cathode emission, beam laminarity and quality of gun fabrication. Any changes in cathode emission, off center placement or tilt of parts which may have occurred during fabrication can be observed and diagnosed from the three-dimensional current density beam profiles. Performance of non-emissive grids or effective ness of grid coatings can be verified. Anomalies in cathode emission, whether due to non-emissive areas or chips or cracks, appear as an irregularity in a cross-section, pseudo-three-dimensional presentation. The cathode edge emission, and change in cathode emission vs. life are easily identified.

Convergent electron gun with bonded non-intercepting control grid

Recent progress in the development of bonded grid guns is described. A gun has been developed and tested in a dual mode helix TWT. The optical performance of this gun was superior to the conventional non-intercepting gridded gun used in this tube.

Electron gun with bonded nonintercepting control grid

The bonded grid consists of a metal-insulator-metal sandwich attached directly to an impregnated tungsten cathode. The metallic top surface of the grid structure is the control grid, and the metallic surface on the bottom provides a diffusion barrier for barium between the cathode and the insulator. The major advantage of this design approach is that the close tolerance required in grid cathode spacings is easily obtained and maintained with the cathode in hot condition. The first bonded grid structure described in the paper was developed for a microwave triode having a grid-to-cathode spacing of 2 mils. The dimensions of the grid cells are 5 × 35 mils. The grid structure consists of a thin wafer of anisotropic boron nitride insulator metallized on both sides by RF sputtering. The fabrication techniques were later extended to construction of convergent guns for linear-beam tubes. The progress and the problem areas experienced in both phases of this program are discussed.

Nonintercepting gridded guns

The major considerations going into the design of nonintercepting gridded guns is discussed and typical performance characteristics of gridded guns in linear-beam tubes are described.