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High Current Low Divergence Ion Beam from a Concave Multiple Aperture Source Electrode

IP.com Disclosure Number: IPCOM000084062D
Original Publication Date: 1975-Sep-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Keller, JH: AUTHOR [+4]

Abstract

It has been found that the extraction of ion beams from a source depends mainly on the shape of the plasma meniscus associated with an ion emitting surface, and the extraction electrodes operatively associated with the surface. As operating conditions of the source change, the shape and position of the plasma meniscus adjusts itself so that the emitted current is space-charge limited. As a result, the ion optical design is very difficult. However, by utilizing a gridded source electrode, the ion-emitting surface in the global sense can be shaped, while the plasma meniscus associated with each opening of the grid may still vary.

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High Current Low Divergence Ion Beam from a Concave Multiple Aperture Source Electrode

It has been found that the extraction of ion beams from a source depends mainly on the shape of the plasma meniscus associated with an ion emitting surface, and the extraction electrodes operatively associated with the surface. As operating conditions of the source change, the shape and position of the plasma meniscus adjusts itself so that the emitted current is space-charge limited. As a result, the ion optical design is very difficult. However, by utilizing a gridded source electrode, the ion-emitting surface in the global sense can be shaped, while the plasma meniscus associated with each opening of the grid may still vary.

In principle, an optimum ion beam may be achieved by balancing the initial beam converging forces due to a concave source electrode with the diverging forces, due to the combination of the electron space charges associated with the ion beam as well as the lens effect of the extraction' electrode. It is possible to achieve ion beams with a divergence angle within + or - 1%.

The apparatus utilized demonstrates the above as shown in the figure. A hot- filament electron impact ion source is operated in the oscillating-electron- discharge mode. The multiple-aperture source consists of about 35 holes in the order of 0.1 inch in diameter, in a concentric circular array over a diameter of 1.2 inches. Each hole is countersunk to form about an 80 degree conical cu...