EP3853879A1

EP3853879A1 - Electron gun

Info

Publication number: EP3853879A1
Application number: EP19769112.4A
Authority: EP
Inventors: Christof Dietrich; Norbert FESTL; Harald Seidel
Original assignee: Thales Deutschland GmbH
Current assignee: GTS Deutschland GmbH
Priority date: 2018-09-20
Filing date: 2019-09-11
Publication date: 2021-07-28
Also published as: WO2020058053A1; US11990307B2; US20210350995A1; DE102018123100A1

Abstract

An electron gun is specified, which comprises: - a cathode, which has a cathode holder and a cathode body; and - a Wehnelt cylinder, wherein the cathode holder receives the cathode body and the Wehnelt cylinder is suitable for bundling free electrons, which can escape from the cathode body toward the Wehnelt cylinder, to form an electron beam, and the Wehnelt cylinder is interlockingly arranged, at least in some parts along a first inner surface facing the cathode holder, on an outer surface of the cathode holder and at least partly extends around the cathode holder.

Description

Electron gun

The invention relates to an electron gun, in particular for

Wandering tubes.

An electron gun is a component by means of which thermal electrons are first generated, then accelerated and within one

Beam path can be focused on a target. The electrons are released from a cathode, to which energy is supplied in the form of heat. The electrons released from the cathode are then subjected to a first focusing by a Wehnelt cylinder, in which the electrons are aligned with an anode, which is usually designed as a pinhole. The electrons are accelerated between the anode, which has a positive electrical potential with respect to the cathode, and the cathode. Known designs for electron guns are, in addition to a large number of other designs, for example the Rogowski electron gun or the Pierce electron gun.

A Wehnelt cylinder focuses electrons into a continuous electron beam. The focusing takes place between the mostly concave Wehnelt cylinder and the anode

Potential difference is generated, so that the electrons are broken along this mostly ideal as a half-shell idealized potential to a common focus.

The focus of the electron beam is of particular importance in the construction of electron guns. Constructive parameters by means of which the focusing and the divergence of an electron beam can be influenced are the shape of the Wehnelt cylinder, the shape of the Anode, the shape of the cathode, the respective potential differences between the components and the design-related distances between the components.

An electron gun is known from US 2006/0091776 A1, in which a disk-shaped cathode is arranged within a hood-like holder on a heating element and a Wehnelt cylinder is arranged around the heating element and the cathode, the Wehnelt cylinder and the

Are cathode spaced apart and thermally and electrically isolated. FR 2 965 971 B1 proposes a support structure for improving the

Alignment of electron guns in which a Wehnelt cylinder with a cathode insulated therein is arranged by means of a series of

Isolation elements against a common carrier housing

is arranged, wherein the carrier housing is simultaneously formed as an anode.

An electron gun arrangement in which a Wehnelt cylinder as well as a cathode and a support structure are connected to one another by means of adjusting screws

can be aligned is known from US 4,900,982. The Wehnelt cylinder, the cathode and the support structure are insulated from each other.

An arrangement in which the electrons are pressed out of the cathode by means of a negatively charged electrode is known from the

US 2008/0211376 A1 known. The Wehnelt cylinder in this font

interacts with the cathode in such a way that a negative potential of the Wehnelt cylinder conducts the electrons within the cathode so that they emerge from the cathode along a preferred axis.

A replaceable cathode is shown in US Pat. No. 3,478,244, the cathode being insulated within a housing and the Wehnelt cylinder likewise being insulated from the housing. Particularly with traveling wave tubes, which are often used in space travel, the focus of the electron beam and thus the mutual alignment of the components of an electron gun and the component strength under load are of particular importance. With regard to the

Complexity in the manufacture of an electron gun, as well as the manufacture of a tube with an electron gun, it is desirable to keep the number of components as small as possible and to keep the alignment of the components with one another as simple as possible. It is therefore the object of this invention to provide an improved electron gun.

This object is solved by the independent claim 1. Further advantageous embodiments of the invention are the subject matter of the subclaims. These can be combined with one another in a technologically sensible manner. The description, in particular in connection with the drawing, additionally characterizes and specifies the invention.

According to the invention, an electron gun is specified which comprises a cathode having a cathode holder and a cathode body and a Wehnelt cylinder, the cathode holder receiving the cathode body and the Wehnelt cylinder being suitable for free electrons which come out of the can emerge in the direction of the Wehnelt cylinder, bundle them into an electron beam and the Wehnelt cylinder is arranged at least in sections along a first inner surface facing the cathode holder in a form-fitting manner on an outer surface of the cathode holder and at least partially surrounds the cathode holder.

Accordingly, an electron gun is specified in which the cathode holder is the central component with the cathode body and also with the Wehnelt cylinder is connected, these components touching each other directly. The Wehnelt cylinder is essentially hollow-cylindrical in shape and receives the cathode holder in its interior in a form-fitting manner, which can be either circular disk-shaped or cylindrical. The cathode holder in turn takes up the cylindrical cathode body in its interior, which can also be hollow cylindrical.

In addition to a hollow cylindrical configuration of the Wehnelt cylinder and cathode holder or a cylindrical configuration of the cathode body, conical configurations are also conceivable. Individual components can only be inserted in one direction and can only be removed in one direction. An embodiment in which the cathode body is frustoconical, the cathode holder is shaped with respect to its inner surface in such a way that it interacts positively with the frustoconical cooling body would be particularly advantageous. Likewise, the Wehnelt cylinder can have the shape of a truncated cone on its inner surface, so that a frustoconical structure of the cathode holder can engage in this inner surface of the Wehnelt cylinder. With such a configuration, the cathode body and the cathode holder could only escape in one direction.

An embodiment in which the cathode body is designed conically and engages in a corresponding inner surface of the cathode holder would also be particularly advantageous. The cathode body can then be introduced into the cathode holder from the direction in which thermal electrons are later emitted. If the Wehnelt cylinder is then additionally designed such that an area which projects in the direction of the central axis of the components and which covers the cathode holder also projects at least partially over the cathode body, the cathode body is trapped and cannot be wise vibrations fall out. Since the cathode holder, the cathode body and the Wehnelt cylinder interlock positively with one another, these components are firmly aligned with one another with respect to their central axis. Accordingly, a later focusing of an electron beam can already be taken into account with regard to the size of the individual components and their shape during manufacture. Accordingly, the components of the electron gun according to the invention are already shaped such that the electron beam can be focused easily and without further processing steps. Compared to the prior art, there are also no further components in the electron gun according to the invention which set a certain distance between, for example, the Wehnelt cylinder and the cathode holder or the cathode holder and the cathode body. The Wehnelt cylinder is provided with an inner surface facing the electrons emerging from the cathode body, to which potential surfaces are formed which bundle and focus the electrons. For this purpose, the area of the Wehnelt cylinder facing the beam axis of the electrons is typically conical in shape toward the cathode body. The cross section of the Wehnelt cylinder can therefore be approximately trapezoidal, semicircular or parabolic in the area facing the beam axis.

According to one embodiment of the invention, the Wehnelt cylinder is at least partially electrically conductively connected to the outer surface of the cathode holder along the first inner surface, and the cathode holder and the Wehnelt cylinder have the same electrical potential.

Contrary to the known solutions and designs for electron guns, there is consequently none between the Wehnelt cylinder and the cathode holder electrical insulator introduced. Wehnelt cylinders and cathode holders therefore have the same electrical potential. This electrical potential will usually be slightly negative with respect to the cathode body, so that the exit of electrons from the cathode body is preferred.

In a further embodiment, a thermal insulator can nevertheless be inserted between the Wehnelt cylinder and the cathode holder. Thus, heat from the cathode body can only be limited to the

Wehnelt cylinders are delivered. The cathode body is heated during operation of the electron gun, so measures like this are necessary to control the heat flow.

In this context, thermal insulation is understood to mean that either a material has been introduced or a constructive precaution has been taken by means of which the corresponding area can be actively cooled. The material should be selected so that it at least inhibits the phononic heat transfer. As active cooling there are slits along which a cooling fluid, such as air, can flow. Compounds from the group of tellurides come into consideration as materials which inhibit the thermal heat flow, or at least the phononic part of the heat flow. For example, bismuth telluride inhibits heat transfer using phonons, but allows electrons to move, so that potential equalization can take place. According to a further embodiment of the invention, an electrical insulator is arranged between the cathode holder and the cathode body, and the cathode holder and the cathode body have an unequal electrical potential. This electrical insulator ensures that when the electron gun is operated along the inner surfaces of the cathode holder, which face the cathode body, an electrical field is created which is oriented in such a way that electrons are displaced within the cathode body in the direction of its central axis. The consequence of this is that the number of electrons per unit time that emerge from the cathode body in the area of the Wehnelt cylinder is increased. The insulator requires a potential separation between the cathode body and the cathode holder. Since according to the invention the Wehnelt cylinder is connected directly to the cathode holder, the isolator between the cathode body and the cathode holder also separates the potential of the Wehnelt cylinder and cathode body.

Instead of a purely electrical insulation between the cathode body and the cathode holder, electrical insulation in connection with a thermal insulation could also be provided, so that the heat flow between the cathode body and the cathode holder is reduced. However, it would also be possible to use only a thermal insulator instead of an electrical insulator, so that the heat flow between the cathode body and the cathode holder is prevented as completely as possible. Due to the thermal separation of the cathode body and the cathode holder, the Wehnelt cylinder is also heated less, so that no or only a few thermal electrons are emitted from the Wehnelt cylinder. For this purpose, it can also make sense for thermal insulation to be introduced between the cathode holder and the Wehnelt cylinder, said insulation being arranged, for example, all around the cathode holder.

According to a further embodiment of the invention, the cathode body is conductively connected at least in sections to an inner surface of the cathode holder and the cathode holder and the cathode body have the same electrical potential. In this embodiment, with reference to one of the previous embodiments, the cathode body, the cathode holder and the Wehnelt cylinder have the same electrical potential. Compared to the prior art, electrical insulation, which causes the Wehnelt cylinder to have a mostly more negative potential than the cathode, is therefore not necessary and is therefore not provided. Regardless of this, however, thermal insulation can be provided between the Wehnelt cylinder and the cathode holder and / or between the cathode holder and the cathode body, so that no heat flow from the cathode body, which is usually heated by an external energy source, to the cathode - holder and there is no heat flow from the cathode holder to the Wehnelt cylinder. Bismuth telluride or lead tellurium can be used as materials which offer good electrical conductivity but also good thermal insulation. Instead of insulation based on material properties, active cooling could also take place, for example by contacting a heat sink.

According to a further embodiment of the invention, the electron gun is provided at least in regions with a non-emitting coating, this non-emitting coating having a greater work of triggering for the emission of electrons than the cathode body.

Thermal electrons can leave a solid-state composite if they have been supplied with sufficient energy in the form of heat. This is desirable in the case of a cathode body of an electron gun. In other areas, however, free electrons emerging from the metal composite are mostly undesirable. In order to avoid these electrons, which are referred to as parasitic interference electrons, the corresponding region from which an exit is undesirable can be cooled. By cooling, the material in the area is kept below the temperature at which Electrons are emitted. Alternatively, however, a material can be applied to the areas from which the escape of thermal electrons is undesirable, which has a high work function and thus inhibits the escape of thermal electrons.

Since, according to one embodiment of the invention, the cathode holder, the cathode body and the Wehnelt cylinder can be in thermal equilibrium, and thus, for example, the Wehnelt cylinder could have approximately the same temperature as the cathode body, is provided by a corresponding coating of the surfaces prevents electrons from being released from the coated area of the Wehnelt cylinder.

According to one embodiment of the invention, the Wehnelt cylinder is provided with the non-emitting coating on a second inner surface facing the electron beam.

When the electron gun is installed, this mostly concave second inner surface lies on a side of the electron gun facing an anode. By coating this second inner surface of the Wehnelt cylinder with a non-emissive material, it is prevented that, starting from the Wehnelt cylinder, electrons are released into the space between the Wehnelt cylinder and the anode.

Overall, it is therefore possible to design the Wehnelt cylinder and the cathode as touching, thermally and / or electrically conductively connected components and to prevent electron leakage from areas where this is undesirable by means of a non-emitting coating. For the purposes of this application, “non-emitting” means that the material and temperature-dependent release work for electrons is greater in the material from which the non-emitting coating is made than in the material of the cathode. de. Low trigger work for the cathode body and high trigger work for the other components of the electron gun are generally intended.

Accordingly, irrespective of thermal and electrical transfers between cathode and Wehnelt cylinder, the escape of thermal electrons from the Wehnelt cylinder must be reduced or prevented by applying a non-emissive coating to parts of the Wehnelt cylinder. In general, this coating could be provided on further components of the electron gun or further components of a tube in which the electron gun is used as an electron source. For example, the collector of a traveling wave tube could be provided with the non-emitting layer at least in some areas.

According to one embodiment of the invention, the non-emissive coating comprises hafnium as a component.

Hafnium has a high release work for electrons with the usual operating parameters of an electron gun. A coating with hafnium or an alloy containing hafnium thus increases the release work in the coated areas, so that fewer electrons or no electrons are released from these areas. According to a further embodiment of the invention, the Wehnelt cylinder is made in two parts, an inner Wehnelt cylinder being surrounded by a hollow cylindrical outer Wehnelt cylinder.

The outer Wehnelt cylinder can advantageously be used as a jet shield to reduce heat radiation from the cathode. According to a further embodiment of the invention, the Wehnelt cylinder and the cathode holder are formed in one piece.

This one-piece design of the Wehnelt cylinder and cathode holder reduces the complexity on the one hand because fewer components are required, and on the other hand the production of an electron gun is particularly easy. The connected component consisting of the Wehnelt cylinder and the cathode holder thus represents an essentially radially symmetrical component which could be manufactured simply and inexpensively using a CNC milling process. Ideally, as in the case of individual components, this connected component is made from a material which has a high release work for electrons and is heat-resistant.

According to one embodiment of the invention, the cathode holder is designed as a hollow cylinder, the inside diameter being dimensioned such that the cathode body can be received in a form-fitting manner in the cathode holder.

Due to the positive reception of cathode bodies in the cathode holder, no additional components, such as for connecting or reducing vibrations, are necessary. The cathode body is often designed as a porous body and could have a carrier in which the material is inserted like a disc. The carrier would then engage in the cathode holder. In the case of the embodiment with an insulation introduced between the cathode holder or the cathode body, this is also hollow-cylindrical in accordance with the shape of the cathode holder and connects the cathode holder and the cathode body in a force-locking manner.

According to a further embodiment of the invention, the cathode holder has on its outer surface a surface that is circumferential to the cathode holder. radially extending step formed at least in sections, the Wehnelt cylinder resting on this step.

Accordingly, a step is provided for the simple and firm connection of the Wehnelt cylinder and cathode holder, on which the Wehnelt cylinder rests in the assembled state. From the other side of the electron gun, ie opposite the Wehnelt cylinder, a carrier device of a tube in which the electron gun is used can correspond to the step. Thus, the electron gun can be easily inserted into a tube and is held in the tube by a support device. Starting from the step, a further carrier device can run in the direction of the beam axis, by means of which, for example, one or more anodes are held. According to a further embodiment of the invention, the cathode body is made of a porous material which is suitable for emitting free electrons when energy is supplied in the form of heat.

The work function essentially depends on material-specific properties. Since it is desired to exit thermal electrons from the cathode, the cathode is made from a low work function material. Since the current of the thermal electrons is proportional to the area from which the electrons are emitted, the material is made porous, ie with a large area.

According to a further embodiment of the invention, the electron gun comprises a pickling device which is suitable for supplying energy to the cathode body in the form of heat, the pickling device being on one of the

Wehnelt cylinder opposite side of the cathode body is arranged and is optionally arranged within the cathode holder. Accordingly, a heating element is provided within the cathode holder, from which heat can be given off to the cathode body, so that the thermal electrons can overcome the work function of the cathode body. The heating device is at least electrically insulating from the cathode body, so that the current flow heating the heating element does not also heat the cathode holder or even the Wehnelt cylinder. It is also expedient for the heating device to be designed thermally with respect to the cathode holder in which it can be arranged. The heating device can also be designed as a rod which engages at least partially in an electrically insulated manner in the cathode body. For simple assembly of an electron gun, the heating device can be arranged within a cylindrical body which corresponds to the inner surface of the cathode holder. It is also possible for the heating element to be assigned to the tube in which the electron gun is used and to be arranged, for example, on a carrier device for the electron gun. According to this, the electron gun would be held in the tube and aligned, among other things, via the heating device.

According to a further embodiment of the invention, the electron gun comprises an anode arranged along its beam axis, the anode having an electrical potential which is positive with respect to the cathode and is electrically insulated from the Wehnelt cylinder, the cathode body and the cathode. Regardless of the potential that exists between the cathode body, the cathode holder and the Wehnelt cylinder, this ensures that the cathode has a negative electronic potential compared to the anode. Electrons that emerge from the cathode body due to heating are thus accelerated in the direction of the anode. Ideally, the anode is convex and, in terms of its shape, corresponding to the Wehnelt cylinder. Det, so that electrons on their way from cathode to anode along the potential surfaces focus on a hole formed in the anode and pass through the hole. In order to ensure a vibration-proof alignment between the cathode and the anode, the anode can be arranged on the Wehnelt cylinder or, for example, on the step of the cathode body by means of an insulated or insulating carrier. Instead of one anode, it is also possible to use several anodes arranged one behind the other in the course of the beam axis.

According to a further embodiment of the invention, the anode can be aligned with respect to the Wehnelt cylinder, the cathode and the beam axis using an adjusting means.

Such an adjustment means could, for example, be one or more screws running radially with respect to the beam axis, via which the anode is connected to an insulating or insulated support structure. By means of the screws, the anode with its central axis, that is, with its hole formed in the middle, could be aligned precisely with the electron beam.

According to a further embodiment of the invention, the components can be aligned with one another in such a way that the electron beam is focused on a target.

In order to ensure that the assembly of a tube is as simple and error-minimized as possible, the electron gun can be focused before it is installed in a tube. On the one hand, this has the advantage that focusing outside the tube can still be carried out easily because the individual components can still be accessed, on the other hand, the complexity when assembling a tube is reduced. With traveling wave tubes, for example, focusing the electron beam is one of the most complex steps in assembling the tube. Assembling traveling wave tubes is made significantly easier with electron guns that have already been focused in advance. In addition, the use of an electron gun with the aforementioned features within a tube is specified as an electron source. Such a tube could be an X-ray tube, for example.

In particular, the use of an electron gun according to one of the aforementioned embodiments is claimed within a traveling wave tube. A traveling wave tube typically comprises a delay line, a collector and an electron source, which is designed as one of the above-mentioned electron guns.

According to the above embodiments, it is possible according to the invention to create an electron gun in such a way that the Wehnelt cylinder is neither thermally or electrically insulated from the cathode, but also no electrons can escape from it, because at least in certain areas it is provided with a non-emissive coating . A particularly simple construction of an electron gun is thus possible without the need to provide further insulators, spacers or cooling elements.

To connect the individual components of the electron gun, these can be connected, for example, with a thermally insulating adhesive. Alternatively, the components could also be screwed on. Some exemplary embodiments are explained in more detail below with reference to the drawing. Show it:

1 shows an electron gun according to the invention in a sectional representation, 2 shows an embodiment of the electron gun according to the invention in a sectional view,

3 shows a further embodiment of the electron gun according to the invention in a sectional view,

Fig. 4 shows a further embodiment of the invention

5 shows a diagram of the individual electrical potentials between individual components of the electron gun according to the invention,

6 shows a traveling wave tube with an electron gun according to the invention in a sectional view, and

7 shows an X-ray tube with an electron gun according to the invention in a sectional view.

In the figures, the same or functionally equivalent components are provided with the same reference numerals.

In Fig. 1, an electron gun EK is shown, which has a Wehnelt cylinder WZ and a cathode holder KH and a cathode body KK having cathode KA. The cathode holder KH receives the cathode body KK along its inner surface Kl. The Wehnelt cylinder WZ in turn receives the cathode holder KH along its outer inner surface WI1 along its outer surface KA. When the electron gun EK is operated, thermal energy is transferred from the cathode body KK into the second inner surface WI2 of the Wehnelt after the supply of energy in the form of heat. Cylinder WZ outlined area. These electrons are then focused and accelerated along an electric field emanating from the second inner surface WI2 of the Wehnelt cylinder WZ in the direction of an anode (not shown in FIG. 1). In contrast to known arrangements, according to the invention the Wehnelt cylinder WZ touches the cathode KA.

FIG. 2 shows an embodiment of the electron gun in which the Wehnelt cylinder WZ touches the cathode holder KH directly, but the cathode holder KH is separated from the cathode body KK by means of an insulation IS. The insulation IS shown there separates the cathode body KK thermally and / or electrically from the cathode holder KH. In the case of an electrical separation by means of the insulator IS, the potential of the Wehnelt cylinder WZ and the cathode holder KH with respect to the cathode body KK could be positive or negative, usually a negative potential of the Wehnelt cylinder WZ, in which the Wehnelt cylinder WZ compared to the Cathode body KK has a negative potential, is preferred.

The electron gun EK shown in FIG. 2 also includes a stage ST on which the Wehnelt cylinder WZ is supported. On its side facing away from the Wehnelt cylinder WZ, the cathode holder KH is also provided with an internal cutout AU, which can engage when using the electron gun EK within a tube arrangement, for example a support structure or a fleece element.

Furthermore, the front side of the Wehnelt cylinder WZ shown in FIG. 2 is inclined significantly more towards a direction of an electron beam in the direction towards the anode, so that the Wehnelt cylinder WZ is shorter along this direction and thus has less mass . In order now to form the potential areas in the shape of a half-shell in accordance with the embodiment shown in FIG. 1 (see also below under FIG. 3), another is external

Wehnelt cylinder WZ 'is provided, which along the direction of an electron Beam encloses the inner Wehnelt cylinder WZ and the cathode holder KH in the form of a hollow cylinder. The outer Wehnelt cylinder WZ 'also serves to shield the heat radiation emitted by the cathode. Instead of inner Wehnelt cylinders WZ and outer Wehnelt cylinders WZ ', one could also speak of a two-part Wehnelt cylinder.

In Fig. 3, a heating element HE is shown, from which energy in the form of heat can be given to the cathode body KK. The heating element HE is arranged inside the cathode holder KH and is thermally and electrically separated from it via a spacer AH. Furthermore, the electron gun shown in FIG. 3 is designed such that the Wehnelt cylinder WZ and the cathode holder KK are provided as a common, one-piece component. The boundaries between the Wehnelt cylinder WZ and the cathode holder KH, as would be present in the design as separate components, are shown in FIG. 3 with a broken line. The electron gun in FIG. 3 has a step ST to which the electron gun can be held within a tube.

An anode AN is arranged on a side of the electron gun EK opposite the heating device HE. Between the anode AN and the concave Wehnelt cylinder WZ, half-shell-shaped potential surfaces PF run as far as possible. Along these potential surfaces PF, thermal electrons released from the cathode body KK are focused in the direction of a pinhole provided in the anode AN. The anode AN itself has a positive potential with respect to the cathode KA, so that the free electrons emerging from the cathode body KK are accelerated toward the anode AN.

Since the Wehnelt cylinder WZ and the cathode holder KK are made in one piece or are not thermally insulated from each other and the cathode body KK is neither thermally nor electrically designed with respect to the cathode holder KH, electrons in the electron gun EK shown in FIG. 3 could also emerge from the Wehnelt cylinder WZ, for example. In order to prevent this leakage of thermal electrons, a non-emitting coating NS can be provided, as shown in FIG. 4. Alternatively, in order to flow the heat flow from the cathode body to the cathode holder, thermal insulation as shown in FIG. 2 can also be introduced between the cathode body KK and the cathode holder in the one-piece embodiment of the Wehnelt cylinder WZ and the cathode holder KH shown in FIG. 3

The non-emissive coating NS shown in FIG. 4 is arranged, for example, along the second inner surface WI2 of the Wehnelt cylinder WZ. This non-emitting coating NS does not release any thermal electrons called interference emissions from this area. Furthermore, a non-emissive coating NS is also provided on the outer surface WA of the Wehnelt cylinder WZ. The meat device HE shown in FIG. 4 is arranged in a support structure TK of a tube, not shown. The support structure TK, which can accommodate the electron gun EK within a tube arrangement, for example, rests on the step ST, as does the Wehnelt cylinder. The non-emitting coating NS can be provided at any point or in any area of the electron gun EK, with a coating being particularly useful in the area of the electron beam. The coating can be vapor-deposited, for example.

5 shows different potential constellations between the Wehnelt cylinder WZ, the cathode holder KH, the cathode body KK and the anode AN. 5A shows a constellation in which the cathode body KK has a low negative electrical potential P2 compared to the Wehnelt cylinder WZ and the cathode holder KH. The higher negative potential P1 is applied to the Wehnelt cylinder WZ and the cathode holder KH. The anode AN has an electrical potential P3 which is negative with respect to the zero point 0, but more positive with respect to the other potentials. The potential distribution shown in FIG. 5A is particularly advantageous because the more negative potential of the cathode holder KH and Wehnelt cylinder WZ forces electrons into the inner region of the cathode body KK, so that in this region the electron density increases and the Trigger work is reduced or the number of electrodes released per unit of time increases. The reverse of this is shown in Fig. 5B.

The potential distribution shown in FIG. 5B again provides a more positive potential P3 for the anode AN, but the lower negative potential P2 is present at the Wehnelt cylinder WZ and the cathode holder KH. The cathode body KK, on the other hand, has the higher negative electrical potential. The result of this arrangement is that the electrons are more concentrated within the edge region of the cathode body KK facing the cathode holder KH. Thus, on the side of the cathode body KK facing the anode AN, an emission takes place predominantly along this edge region.

5C shows an embodiment in which the Wehnelt cylinder WZ, the cathode holder KH and the cathode body KK are not insulated from one another. There, the Wehnelt cylinder WZ, the cathode holder KH and the cathode body KK all have the higher negative electrical potential P1.

5C, the anode AN again has the more positive potential P3.

Although in FIG. 5C all components except the anode AN have the same higher negative electrical potential P1, these components could at least be thermally insulated from one another. It should be noted in Fig. 5 that it it is a non-scaled axis from which only the polarity of an electrical potential and thus also the direction of an electrical field between individual components can be taken. The absolute amount of individual potential differences cannot be found in FIG. 5.

FIG. 6 shows a traveling field tube arrangement WR in which an electron gun EK according to the invention is connected to the tube RO via a support structure TK. The anode AN of the electron gun EK is also connected via a support structure PK. The support structure TK of the anode AN rests on the stage ST of the electron gun EK. The TK support structures are each electrically insulated. In the course of the electron beam ES starting from the electron gun EK, a helical delay line FIX follows, into which electrical signals are fed from an input IN to an output OFF. Around the delay line FIX is a magnetic focusing device ME, which forms the electron beam within the delay line FIX. After the delay line FIX, the collector KO follows in the path of the electron beam ES, in which the electrons of the electron beam ES are collected. Since the electron gun EK with its anode AN, its Wehnelt cylinder WZ, its cathode holder KH and the cathode body KK and the filler element HE was already focused before being inserted into the tube RO, this step no longer had to be carried out when assembling the traveling wave tube WR . The provision of an already pre-focused electron gun thus saves time in the firing of traveling wave tube arrangements WR.

Another tube, namely an X-ray tube, is shown in FIG. A preconfigured electron gun EK, the components of which were already coordinated with one another with regard to the focusing of the electron beam, was also installed in FIG. 7. The electron beam ES from the Electron gun EK goes out, is passed to an anti-cathode UK with an anode AN behind it, the electrons being braked so strongly when the electrons of the electron beam ES strike the anti-cathode UK that this X-ray radiation RS in a direction specified by the anti-cathode submit.

In general, the electron gun, as described in this application, can be used in all tubes that require an electron source in the form of an electron gun.

For reasons of clarity, none of the figures shows electrical supply or discharge lines and a corresponding power supply.

The features specified above and in the claims, as well as those that can be gathered from the illustrations, can advantageously be implemented both individually and in various combinations. The invention is not limited to the exemplary embodiments described, but rather can be modified in many ways within the scope of expert knowledge.

Claims

Expectations:

1. Electron gun (EK) comprising a cathode (KA) and a cathode body (KK) having a cathode (KA) and a Wehnelt cylinder (WZ), the cathode holder (KH) receiving the cathode body (KK) and the Wehnelt -Cylinder (WZ) is suitable to bundle free electrons that can emerge from the cathode body (KK) in the direction of the Wehnelt cylinder (WZ) to form an electron beam (ES), and the Wehnelt cylinder (WZ) at least in sections along a first inner surface facing the cathode holder (KH)

(WH) is arranged in a form-fitting manner on an outer surface of the cathode holder (KA) and at least partially closes the cathode holder (KH).

2. Electron gun according to claim 1, wherein the Wehnelt cylinder (WZ) along the first inner surface (WH) is at least partially electrically connected to the outer surface (KA) of the cathode holder (KH) and the cathode holder (KH) and the Wehnelt Cylinder (WZ) have the same electrical potential.

3. Electron gun according to one of claims 1 or 2, in which an electrical insulator (IS) is arranged between the cathode holder (KH) and the cathode body (KK) and the cathode holder (KH) and the cathode body (KK) have an unequal electrical one Have potential.

4. Electron gun according to one of claims 1 or 2, in which the cathode body (KK) is at least partially electrically conductively connected to an inner surface (Kl) of the cathode holder and the cathode holder (KH) and the cathode body (KK) have the same electrical potential.

5. Electron gun according to one of claims 1 to 4, in which the

Wehnelt cylinder is made in two parts, with the inner Wehnelt

Cylinder (WZ) is surrounded by a hollow cylindrical outer Wehnelt cylinder (WZ ').

6. Electron gun according to one of claims 1 to 5, which is at least partially provided with a non-emitting coating (NS), the non-emitting coating (NS) having a larger release work for the emission of electrons than the cathode body ( KK)

7. Electron gun according to claim 6, in which the Wehnelt cylinder (WZ) is provided with the non-emitting coating (NS) on a second inner surface (WI2) facing the electron beam (ES).

8. Electron gun according to one of claims 6 or 7, wherein the

Wehnelt cylinder (WZ) is provided with the non-emitting coating (NS) on an outer surface (WA).

9. Electron gun according to one of claims 6 to 8, whose non-emissive coating comprises hafnium as a component.

10. Electron gun according to one of claims 1 to 9, wherein the

Wehnelt cylinder (WZ) and the cathode holder (KH) are made in one piece.

11. Electron gun according to one of claims 1 to 10, in which the cathode holder (KH) is of hollow cylindrical design, the inside diameter being dimensioned such that the cathode body (KK) is positively received in the cathode holder (KH) can.

12. Electron gun according to one of claims 1 to 11, in which the cathode holder (KH) has on its outer surface (KA) a radially extending step (ST) formed at least in sections with respect to the circumference of the cathode holder (KH), the Wehnelt cylinder (WZ) rests on this level.

13. Electron gun according to one of claims 1 to 12, the cathode body (KK) is made of a porous material which is suitable when emitting energy in the form of heat to emit free electrons.

14. Electron gun according to one of claims 1 to 13, which comprises a heating device (HE) which is suitable for supplying energy to the cathode body (KK) in the form of heat, the heating device (HE) on one of the Wehnelt Cylinder (WZ) opposite side of the cathode body (KK) is arranged.

15. Electron gun according to claim 14, the heating device (HE) of which is arranged inside the cathode holder (KH).

16. Electron gun according to one of claims 1 to 15, which comprises an anode (AN) arranged along the beam axis (SA), the anode (AN) having a positive electrical potential with respect to the cathode (KA) and with respect to the Wehnelt cylinder (WZ), the cathode body by (KK) and the cathode (KA) is electrically isolated.

17. Electron gun according to one of claims 1 to 16, the anode (AN) of which can be aligned with respect to the Wehnelt cylinder (WZ), the cathode (KA) and the beam axis (SA) via an adjusting means.

18. Electron gun according to one of claims 1 to 17, the components of which can be aligned with one another in such a way that the electron beam (ES) is focused on a target.

19. Tube arrangement with an electron gun (EK) according to one of claims 1 to 18, in which the electron gun (EK) is arranged inside the tube (RO) as an electron source.

20. Traveling wave tube (WR) with an electron gun (EK) after one of the

Claims 1 to 18, which comprises a delay line (HX) and a collector (KO), the electron beam (ES) during operation of the traveling wave tube (WR) through the delay device which runs in a spiral from the electron gun (EK) to the collector (KO) (HX) is guided and the collector (KO) forms the target for the electron beam (ES) in which the electrons are captured.