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Neutralizer for Hall-Current Accelerator

IP.com Disclosure Number: IPCOM000046109D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 60K

Publishing Venue

IBM

Related People

Cuomo, JJ: AUTHOR [+2]

Abstract

Hall-current accelerators are used for many purposes, including the provision of ion beams in industrial applications. In many applications, the ion beam must be neutralized. An improved neutralizer is described which is located at the center of the hall accelerator, and is preferably a hollow cathode electron source.

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Neutralizer for Hall-Current Accelerator

Hall-current accelerators are used for many purposes, including the provision of ion beams in industrial applications. In many applications, the ion beam must be neutralized. An improved neutralizer is described which is located at the center of the hall accelerator, and is preferably a hollow cathode electron source.

A Hall-current accelerator is illustrated in Fig. 1. Essentially radial magnetic field lines 1 are produced by pole pieces 2 and 3. The pole pieces are made of a permeable material, such as mild (low carbon) steel, and are polarized by electromagnets or permanent magnets (not shown). Electrons (not shown) are emitted by a cathode 4 near ground potential. The electrons flow to the anode 5. The interaction of these electrons with the magnetic field results in their precession in the azimuthal direction (around the center pole piece 2), thereby producing the circulating "Hall current" and establishing the electric field that accelerates the ions (also not shown). The ions are produced near the anode, either by the electrons from cathode 4 or by other electrons emitted from an additional cathode (not shown) nearer the anode. The ions are accelerated to the right due to the electric field described above, forming an ion beam 6 which impinges on a target 7. Since the actual recombination of ions with electrons is usually a negligible process, it is necessary to supply equal quantities of electrons and ions to the target 7, if the target is electrically isolated. Such isolation is often associated with the sputtering of insulator surfaces. The electrons added to the ion beam to offset the space charge and/or current of the ions are called neutralization electrons.

The neutralization electrons can be drawn from cathode 4, in addition to the electrons already being drawn from cathode 4 to the anode 5. It is necessary, however, for such neutralizing electrons to pass through the fringe magnetic field, located mostly to the right of pole pieces 2 and 3 in Fig. 1. This fringe magnetic field produces an electrical impedance that prevents the free flow of electrons from cathode 4 to target 7. The flow of neutralization electrons from cathode 4 to target 7 is thus associated with the target rising to some positive potential sufficient to draw the required neutralization electrons.

Location 9 in Fig. 1 is particularly suited for a neutralizer cathode of a Hallcurrent accelerator. Being a central location, it is inherently axially symmetric. Because of the axial orientation of the magnetic field lines near the axis of symmetry, electrons can flow easily from location 9 to target 7. The magnetic field strength near the target is normally low enough that the electrons would be distributed over the entire target area with driving potential differences of several volts, or less.

The central location 9 for a neutralizer is one aspect of this accelerator, with symmetry and easy coupling to the targe...