Varian Associates, Inc.

Gerhard B Kuehne

George V Miram

A gun for a linear-beam electron tube has a control grid for modulating the beam current which consists of an array of conductive web elements whose spacing from each other is much larger than their spacing from the concave emissive surface of the cathode. It was found that when this condition is met the grid can be operated at cathode potential while beam current is being drawn without distorting the electric accelerating field enough to ruin the focusing of the beam. Thus, when the grid is used to pulse the beam current on and off, it can have zero bias in the 'on' condition, whereby the pulse modulator can be greatly simplified.

Zero-bias gridded gun

The electron gun includes a spherically concave cathode emitter with a pair of axially spaced spherically concave focus and control grids closely spaced overlaying the cathode emitter for controlling the beam current. The grids are supported from a common thermally conductive tubular grid support structure via the intermediary of first and second annular members one of which is a thermally conductive insulator. One or more of the grids are serrated about their peripheries to define a plurality of radially directed fingers bonded to the end of a respective annular grid support member. In an alternative embodiment, the end of the annular grid support member, as bonded to the serrated grid, is castellated to accommodate differences in thermal expansion between the grid and the annular grid support member.

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Santa Clara, CA, United States of America

Gerhard B Kuehne