DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a conventional surface emitter with a focusing element in a plan view and in section.
FIG. 2 shows a surface emitter in accordance with the invention with a focusing element in a plan view and in section.
FIG. 3 shows, in plan view, an emitter plate in accordance with the invention having a central region connected via a connection web with the adjoining region.
FIG. 4 shows in plan view, an emitter plate in accordance with the invention having a central region connected with the adjoining region via two connection webs at the same potential.
FIG. 5 shows in plan view, an emitter plate in accordance with the present invention having a central region connected with the adjoining region via two connection webs at different potentials.
FIG. 6 shows in plan view, an emitter plate in accordance with the invention designed for connection to two circuits.
FIG. 7 schematically illustrates a surface emitter with a diaphragm plate arranged before the central region of the emitter plate in accordance with the invention, in plan view and in section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a conventional surface emitter 1 in a plan view and in section. The plan view shows the emitter plate 2 with a central region 3 (dark hatching) and the region 4 (light hatching) adjoining this central region 3. The emitter plate 2 is surrounded by an annular focusing element 5. The vertical dashed line proceeding through the center point of the emitter plate 2 symbolizes the section plane for the section drawing.
The heater 6 that heats the emitter plate 2 by means of a heating current 7 is schematically shown in the section drawing. In a conventionally-designed surface emitter 1 the central region 3 emits an electron beam of high density 8′. This is shown dark in order to indicate the high electron density. The region 4 adjoining this central region 3 emits an electron beam of medium density 8. The focusing element 5 arranged around the emitter plate exhibits the shape of a flat cylinder open at one side, with the emitter plate 2 arranged on the cylinder base. The focusing effect of the focusing element 5 is indicated by a convergence of the electron beams of high density 8′ and medium density 8.
In plan view and in section, FIG. 2 shows an inventive surface emitter 1. FIG. 2 corresponds to FIG. 1, but with the important difference that the central region 3 in the emitter plate 2 of the inventive surface emitter 1 emits an electron beam of lower density 8″. This is indicated in FIG. 2 by both the region 3 and the electron beam of lower density 8″ being shown without hatching. In the section view it can be seen that focusing of the electron beam 8, 8″ is achieved by means of the focusing element 5. Since no electrons or only few electrons are emitted from the central region 3 at the starting point of the electron beam, a lesser beam expansion due to mutually repelling electrons ensues than in the case of FIG. 1, where an electron beam of high density 8 is emitted in the central region 3. Given a predetermined distance between the surface emitter 1 and an anode (not shown), an improved focusing thus can be achieved while retaining the focusing element 5 with identical focusing parameters.
In the plan view of FIG. 3 a further embodiment of an emitter plate 2 of a surface emitter 1 is shown. Slits 9 are introduced into the emitter plate 2 such that a serpentine current path 10 is generated between the two heating current connections 11, 11′. These current paths proceed only in a region 4 of the emitter plate 2 that adjoins the central region 3. The central region 3 is connected with the adjoining region 4 only via a connection web 12. If a heating current is applied to both heating current connections 11, 11′, the heating voltage drop along the current path 10 heats only the adjoining region 4 to cause it to emit electrons. Heating current does not flow through the central region 3. The central region 3 is heated only by heat conduction from the adjoining region 4 through the narrow connection webs 12. The central region 3 therefore emits no electrons, or nearly no electrons.
The emitter plate 2 exhibits an outer contour 2′ that is circular. The central region 3 of the emitter plate 2 likewise exhibits a circular outer contour 3′. Only the region 4 (which is fashioned in the manner of a washer) adjoining the central region 3 thus emits electrons. Since no electrons are emitted in the central region 3, this leads to a lower expansion of the electron beam (as illustrated in the explanation regarding FIG. 2) since the electrons repel each other less strongly. The electron beam thus can be focused better in comparison to an electron beam emitted from a conventional surface emitter. Since the electron beam additionally exhibits a rotationally symmetrical geometry, a surface emitter I with such an emitter plate 2 is suitable for rotary piston radiators.
FIG. 4 shows a further variant of an emitter plate 2 for a surface emitter 1. The single difference from the emitter plate 2 shown in FIG. 3 is that the central region 3 is connected with the adjoining region 4 via two opposing connection webs 12. The two connection webs 12 are at the same potential given a heating current applied to the emitter plate. At maximum, a very small heating current therefore flows transversely across the central region 3 when the connection webs are executed sufficiently wide. A heating of the central region therefore likewise occurs exclusively or almost exclusively via heat conduction through the two connection webs 12. The two connection webs 12 lead to an increased mechanical stability of the emitter plate.
FIG. 5 shows an emitter plate of a surface emitter 1 in which, as in FIG. 4, the central region 3 is likewise connected with the adjoining region 4 via two connection webs 12, but the two connection webs 12 are not at the same potential, meaning that the angle a between the two connection webs 12 exhibits a value differing from 180°. The position of the both connection webs 12 is unambiguously determined by means of the angle β between the perpendicular bisector of the side and one of the two connection webs 12. Given application of a heating current at the two heating current connections 11, 11′, a potential difference exists between the two connection webs 12. The magnitude of this potential difference (and thus the magnitude of the heating current flowing between the two connection webs) can be adjusted by selection of the angle between the connection webs 12. The electron density distribution for the central region thus can be set within a very broad range by the selection of the angle between the two connection webs 13. In contrast to the embodiments for the emitter plate 2 described in FIG. 3 and FIG. 4, with regard to the electron density distribution there is no steep decline between the adjoining region 4 and the central region 3 but rather a sliding transition. A further improvement of the electron density distribution at the anode location can be achieved with the focusing of the electron beam.
FIG. 6 shows an emitter plate 2 of a surface emitter 1 has heating current connections 11, 11′ for a first heating current circuit and heating current connections 14, 14′ for a second heating current circuit. The connections 11, 11′, 14, 14′ are respectively arranged offset in pairs by 90°. The arrangement of the slits 9 for generation of the current paths 10 on the emitter plate 2 is executed such that heating currents respectively flow between the heating current connections 11, 11′ and between the heating current connections 14, 14′. Since the current paths are executed symmetrically in this case, no heating current or nearly no heating current flows in the central region 3 of the emitter plate 2. The electron density distribution of the electrons emitted from the central region 3 is variable in a very broad range by a suitable arrangement of the current paths 10 as well as the heating currents flowing between the heating current connections 11, 11′ and 14, 14′. The initially higher expenditure to provide two pairs of heating current connections 11, 11′, 14, 14′ as well as the associated heating current circuits provides the advantage of allowing a specification of the electron density distribution, which allows the electron density distribution to be optimized to the focal spot at the anode. The outer contour 3′ of the central region 3 is shown dashed in order to indicate that it can be adjustably (selectively) set. This embodiment enables the electron density to be adjusted solely by suitable control of the heating current connections 11, 11′ and 14, 14′. A further advantage of the arrangement shown in FIG. 6 is that the emitter plate 2 exhibits a higher mechanical stability than in the variants shown in FIG. 3 through FIG. 5 with one or two connection webs 12.
All emitter plates 2 in FIG. 3 through 6 additionally exhibit the advantage that ions that are kicked out at the anode and strike on the emitter plate 2, in the central region 3 barely influence the electron density distribution of the emitter plate 2, since the central region 4 is of subordinate importance for the electron density distribution.
FIG. 7 shows in plan view and a section through a surface emitter 1 with an emitter plate 2 having a diaphragm plate 15 with a circular outer contour 15′ located in front of the central region 3. The focusing element 5 exhibits the same geometric properties as described herein regarding FIG. 1 and FIG. 2. The use of a conventional emitter plate 2 is possible due to the diaphragm plate 15 arranged in front of the emitter plate 2. Electrons exiting from the central region 3 of this emitter plate 2 strike on the diaphragm plate 15 and are not accelerated in the direction toward the anode. The diaphragm plate 15 additionally serves as protection from ions produced from the anode that are accelerated in the direction of the emitter plate 2. These ions strike the diaphragm plate 15 and thus can cause no mechanical damage to the emitter plate 2. The variant with the diaphragm plate 15 placed in front leads to an electron density distribution comparable to the variants for the emitter plate 2 described in FIG. 3 and FIG. 4. This is a particularly simple and cost-effective variant.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
Patent Application
20070246789
