Browse Prior Art Database

Reduction in Ion Beam Energy Spread by Space Charge Control

IP.com Disclosure Number: IPCOM000049448D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Harper, JME: AUTHOR [+2]

Abstract

A technique is described which controls the energy spread of an ion beam by simple electrical means. There is also provided means for rapid control over the current density in the beam.

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Reduction in Ion Beam Energy Spread by Space Charge Control

A technique is described which controls the energy spread of an ion beam by simple electrical means. There is also provided means for rapid control over the current density in the beam.

The essence of the technique is to make use of the space charge potential developed in a high current density ion beam. The space charge is used to control the ion flux in the beam itself.

Control over this space charge effect is provided by a grid or mesh structure placed across the beam. By varying a single voltage applied to this mesh, the space charge effect can be minimized or maximized, causing a rapid and distinct change in the transmitted beam characteristics.

In particular, by appropriate choice of dimensions and voltages, the transmitted beam current density and energy spread can be switched between two widely different values by a small change in control voltage applied to the grid.

Shown in Fig. 1 is an example of the technique. An incident ion beam of current density j(o) and energy E(o) (with spread Delta) is directed at a grid structure which is used to control the beam. The grid array consists of two grounded grids (fine mesh) with a center grid which can be electrically biased by a control voltage V(c).

For small positive values of V(c), the incident ion beam is fully transmitted, with its current density and energy spread unchanged.

However, when the positive control voltage V(c) reaches a critical value V(crit), the transmitted ion current density abruptly drops to a fraction of the incident value, and the energy spread narrows sharply.

These changes are shown in Fig. 2. When V(c) exceeds the ion energy E(o), no ions are transmitted.

This abrupt chan...