| 摘要 |
Specially shaped filaments improve the performance of Freeman ion sources. There are many different filament shapes covered by this invention. These shapes have two features in common-they have flat surfaces or facets, and two of these facets must join to form a knife edge. It is the purpose of these facets to direct negative ions away from the extraction slit. These negative ions are emitted from the filament normal to the surface. If the knife edge is directed toward the slit, very little of the negative ion flux can enter the extraction slit. In effect, the filament becomes invisible at the slit as far as negative ion flux is concerned. A converse application in which a large negative ion flux is desirable, requires shaping of the filament with a smooth concave surface in order to maximize the cathode surface normal to the extraction slit.
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