EMITE ARRAY FOR AN ELECTRON GUN, ACTIVELY COOLED BEAM GUIDE AND AXIAL ELECTRON GUN

Abstract

Emitter arrangement (11) for an electron gun (10), comprising: an actively cooled cathode block (20), and an accelerator anode (15), preferably ring-shaped; wherein the cathode block (20) comprises: a heat sink (21); an emitter assembly (23 - 28); and an insulator (22) which is arranged in a thermally conductive manner between the heat sink (21) and the emitter assembly (23 - 28), wherein the insulator (22) has a thermal conductivity λ greater than or equal to 20 W / (m · K), preferably greater than or equal to 50 W / (m · K) and more preferably greater than or equal to 90 W / (m · K).

Description

1. Technical field

[0001] The invention relates to an electron gun for the vapor deposition of materials in a high vacuum (PVD). Such electron beam evaporators are used in industrial coating technology to deposit thin films onto surfaces at high rates. Examples include, among others, aluminum layers as a water vapor diffusion barrier on plastic film, metal contact layers, insulating or dielectric layers made of metal oxides for optical components, or high-temperature superconductor (HTS) layers on thin metal foils for the production of superconducting ribbon conductors. 2. State of the art

[0002] Evaporation of materials in a high vacuum using an electron beam is an established process. Accordingly, there is a wide variety of electron guns and beam generators available. Compact electron beam evaporators are particularly popular in the development and coating of optical components. In these devices, the beam generation unit is located directly on the evaporation crucible, and the electron beam is passively focused by a magnet, directed at a 270° angle onto the crucible.

[0003] An early example of this arrangement can be found in DE 2 442 032 A1. EP 1 204 507 and EP 1 830 382 describe cathode arrangements for arc-free beam generation. However, due to the emitter being located close to the evaporation crucible, the crucible is easily fouled, and this arrangement is not suitable for evaporating larger quantities of material exceeding 100 g. The service life of these evaporators is limited when evaporating larger quantities of material. Axial electron guns, which can be separated from the evaporation crucible, are therefore better in terms of long service life and larger material quantities, as this significantly reduces the fouling of the emitter due to the distance. Axial electron guns typically comprise a source section where the beam is generated and a beam tube in which the electron beam is focused and deflected, ensuring that the power density required for evaporation is available at the crucible.Various concepts for generating the electron beam are known from the prior art.

[0004] For example, electron beams can be generated via a cathode with a Wehnelt cylinder (see DE 1953 722 9 or EP 3 238 98 B1), from hollow cathodes with displacers (see DE 10 2016 120416), from field emission tips (see DD 2 878 56) or by massive, heated cathodes in the so-called Pierce geometry, as described in DD 1 323 80 A1 or EP 2 077 574 B1.

[0005] When generating beams from tips or Wehnelt cylinders, high beam powers are only achieved through very high accelerating voltages – typically higher than 60 kV, often more than 100 kV. This makes the power supply for the electron gun very expensive. Another problem is that axial electron guns must be very large and require special safety concepts, as hard X-rays are generated in such coating systems. Furthermore, beam generation in these configurations is highly dependent on the precise alignment of the electron gun's components. Therefore, maintenance is complex and can only be performed by qualified personnel, which in turn increases costs and reduces the operating life of the electron gun.

[0006] Conventional Pierce emitters, on the other hand, can generate electron currents >500 mA, allowing for a lower accelerating voltage. Typically, this voltage ranges between 10 and 30 kV.

[0007] The massive cathode also makes the Pierce electron gun robust against ion bombardment and wear. If positively charged ions are generated in the area of ​​the source unit – e.g., from residual gas or penetrating reactive gas – the ions are accelerated towards the cathode and cause material erosion upon impact.

[0008] Fig. Figure 1 shows an example of the axial electron gun in Pierce configuration as described in EP 2077574 B1, to illustrate the basic structure. The left part shows the source section 31 of the electron gun, comprising the massive, planar cathode 37, which is heated from behind by electron bombardment via a filament 36. Also shown are the Wehnelt electrodes 38 for focusing the extracted electrons and the anode 39, which forms the transition to the beam tube 30 with the electron optics 40, 41.

[0009] Furthermore, it is known from the prior art that the service life of the electron gun in operation can be increased if the beam generation area is pumped differentially to reduce the residual gas pressure, as described, for example, in DE 4 428 508.

[0010] Furthermore, it is known that the penetration of gas from the coating area can be made more difficult by apertures, as described in DE 1 973 0855. Alternatively, the incident ions can be directed into a cavity in the center of the cathode, a so-called ion sump (see JP 2005 / 268177).

[0011] The publication ME Herniter et al., Thermionic cathode electron gun for high current densities, IEEE transactions on plasma science 15 (1987), p. 351-360, concerns an emitter for an electron gun based on the Pierce principle in which an anode ring is mounted over a water-cooled stainless steel cylinder.

[0012] The publication by S. Uhlemann et al., "Thermal magnetic field noise limits resolution in transmission electron microscopy," Physical Review Letters 111 (2013), pp. 46101-1–46101-5, addresses the improvement of imaging in a transmission electron microscope. Thermal noise in the metallic wall of the beamline leads to magnetic interference fields and increased electron scattering, thus reducing image contrast. A beamline cooled to 120 K with liquid nitrogen reduces the noise and improves image quality.

[0013] US 2006 / 0188069 describes an X-ray tube with a rotating anode and cooled housing and an electron gun (17).

[0014] US 5,973,447 describes a gridless ion source with a hollow anode in which a plasma is ignited and from which ions are extracted. These are neutralized by a laterally mounted electron source (cathode). This includes an emitter and an aperture assembly.

[0015] DE 195 37 229 describes an electron gun design with thermal contact between the inner cage and the housing.

[0016] However, electron guns known from the prior art have several disadvantages.

[0017] For example, the electron beam evaporators described above with a 270° deflection, while compact and inexpensive, are not suitable for large evaporation rates. Due to the immediate proximity of the evaporation crucible, which is a significant source of fouling, the cathode and other high-voltage components become heavily coated. This can lead to electrical discharges and arcing over time, potentially causing power outages or damage. Furthermore, positively charged ions generated above the crucible are accelerated by the accelerating voltage, moving in the opposite direction to the electrons towards the filament. Upon impact, these ions coat the filament wire, damaging and potentially destroying it. Therefore, at high evaporation rates, the operating time of such evaporators is limited to just a few hours before maintenance (e.g., cleaning and filament replacement) becomes necessary.Therefore, such evaporators are unsuitable for continuous processes with large quantities of exhaust steam.

[0018] While axial electron guns known from the prior art achieve long operating lifetimes, they are very complex in design, expensive, and, above all, heavy and difficult to maintain. A common characteristic of all these designs is that beam generation in the source region is highly sensitive to the spacing of the components in the emitter and their alignment. To make matters worse, the area around the emitter becomes very hot due to the heating of the cathode or the impact of high-energy electrons. This causes the components to expand and alters the alignment. The beam tube itself can also be severely heated and even destroyed by impacting electrons if it is poorly aligned.

[0019] Even under normal operating conditions, contamination accumulates over time in the source section, which can significantly impair the field configuration in the emitter and the lifespan of the components. This is caused by positive ions generated in the source area through impact ionization in the residual gas. These ions are accelerated towards the cathode, causing it to erode. Sputtered material (e.g., tungsten and tungsten oxide) deposits on adjacent components and insulators, altering the electrical conductivity of their surfaces. The high temperatures in this area also cause scaling of screw connections, complicating the loosening and reuse of these parts, general maintenance, and filament changes.

[0020] The underlying problem of the present invention is therefore to at least partially reduce some of these disadvantages of the prior art. 3. Summary of the invention

[0021] The problem mentioned above is at least partially solved by the subject matter of the independent claims of the present invention. Exemplary embodiments are described in the dependent claims.

[0022] In one embodiment, the present invention provides an emitter arrangement for an electron gun for vaporizing coating material, comprising an actively cooled cathode block and an accelerator anode, preferably ring-shaped, wherein the cathode block comprises a heat sink, an emitter assembly and an insulator which is arranged thermally between the heat sink and the emitter assembly and wherein the insulator has a thermal conductivity λ greater than or equal to 20 W / (m · K), preferably greater than or equal to 50 W / (m · K) and more preferably greater than or equal to 90 W / (m · K).

[0023] Here and in the following, temperature-dependent material properties such as thermal conductivity λ or specific electrical resistance ρ at a temperature of 100°C will be specified.

[0024] In particular, the active cooling of the emitter assembly via the highly thermally conductive insulator ensures that all components relevant for adjusting the emitter arrangement remain dimensionally stable and do not scale. Furthermore, due to the design, all parts that can become contaminated and require regular cleaning are very easily and quickly accessible and can be safely replaced and installed by a mechanic without high-voltage qualifications.

[0025] As explained below, such an emitter arrangement makes it possible to construct electron guns that require significantly less maintenance and have a significantly longer service life in continuous operation than the electron guns known from the prior art for evaporating coating material in a vacuum.

[0026] In particular, the insulator can be made of a highly thermally conductive ceramic or a plastic with highly thermally conductive ceramic filler material, wherein the ceramic material preferably comprises a compound of elements of the III and V main groups, more preferably of Al2N3 and / or BN.

[0027] Furthermore, the insulator can have a specific resistance ρ greater than or equal to 10 9 Ω · cm, preferably greater than or equal to 10 10 Ω · cm, preferably greater than or equal to 10 11 Ω · cm, and most preferably greater than or equal to 10 12Ω · cm and / or the insulator can have an electrical breakdown strength of greater than or equal to 40 kV / mm, preferably greater than or equal to 50 kV / mm and more preferably greater than or equal to 65 kV / mm.

[0028] By using such insulators between the heat sink and the emitter assembly, complete electrical isolation of the emitter assembly and efficient heat dissipation can be ensured even with compact designs, high acceleration voltages and strong beam currents.

[0029] For example, in some embodiments the emitter arrangement can generate an electron beam with a power of 0.5 kW - 36 kW, preferably with a power of 1 - 15 kW, and / or generate an electron beam with an effective beam current of 100 mA - 1200 mA at an accelerating voltage of 5 - 30 kV, preferably 6 - 12 kV.

[0030] For example, the temperature of the emitter assembly, measured at the outer edge of the surface of the emitter assembly facing the accelerator anode, may not exceed 200°C, preferably not exceed 175°C, and more preferably not exceed 150°C, and / or the accelerator anode itself may also be actively cooled, so that during operation of the emitter arrangement the temperature of the accelerator anode, measured at the outer edge of the accelerator anode, is not exceeding 200°C, preferably not exceeding 175°C, and more preferably not exceeding 150°C.

[0031] The resulting temperature gradients across the various components and assemblies of the emitter arrangement prevent material stresses and a consequent misalignment of the emitter arrangement.

[0032] Furthermore, in some embodiments, the heat sink can have at least one cooling channel through which a cooling medium, preferably water, can flow, and / or the heat sink can be made of a material, preferably copper or aluminum, which has a thermal conductivity λ greater than or equal to 200 W / (m·K), preferably greater than or equal to 300 W / (m·K).

[0033] In this way, the heat transferred from the emitter assembly to the heat sink via the highly thermally conductive insulator can be efficiently absorbed and dissipated by the heat sink. This further increases the compactness of the emitter assembly and reduces maintenance requirements.

[0034] In some embodiments, the emitter assembly of the emitter arrangement can have two electrically isolated subunits, the surfaces of which facing the anode ring form an at least partially concave depression into which a heating coil, preferably a tungsten filament, is inserted.

[0035] In this way, despite the accelerating voltage in the kV range applied to the emitter assembly, a sufficiently strong heating current can be directed through the heating coil facing the accelerator anode. Furthermore, the concave surfaces of the two subunits result in an electric field distribution of the accelerator field that efficiently focuses and aligns the electrons emitted from the heating coil onto the opening of the accelerator anode.

[0036] Furthermore, the center of the heating coil can be omitted and / or the heating coil can be designed as a flat spiral, so that the electrons are emitted from a planar arrangement. The heating coil can have a heating power of greater than or equal to 150 W, preferably greater than or equal to 200 W.

[0037] The recessed center of the heating coil prevents a large proportion of the generated residual gas ions, which are accelerated towards the emitter arrangement, from hitting the heating coil and damaging it.

[0038] Furthermore, a central channel can be arranged in the cathode block of the emitter arrangement, leading into an ion sump in which positive ions are stopped in a replaceable ion absorber, preferably a rotatable ceramic pill, which serves as sacrificial material.

[0039] This arrangement protects not only the filament but also the field-generating, concave surfaces of the emitter assembly from bombardment with positively charged ions. The rotatable and replaceable sacrificial material reduces maintenance and material wear.

[0040] Furthermore, in some embodiments the accelerator anode may have an aperture with a mean diameter of 5 mm to 8 mm and / or the emitter arrangement may have a connection for a vacuum pump or a bypass and / or a background gas pressure of at most 5 · 10 in the emitter arrangement (11). -5 mbar predominates.

[0041] For example, the emitter assembly can be differentially pumped out by a turbomolecular pump with a pumping rate of up to 80 1 / s. Together with the aperture of the accelerator anode, this results in a gas pressure of less than or equal to 5 × 10⁻⁶ in the emitter assembly. -5 mbar (i.e. 5 · 10-3 Pa) can be maintained. This allows the electron beam gun to operate continuously even in reactive atmospheres (e.g., oxygen, H2O) at up to 10 -3 mbar (10 -1 Pa) in the evaporation range. If a turbomolecular pump is not used in the coating chamber, provided the vacuum quality is sufficient, the emitter arrangement can be connected to the main chamber via a bypass for easier evacuation.

[0042] In a further embodiment, the present invention provides an actively cooled beam guidance device for an electron gun, comprising: a beam tube having at least one cooling channel through which a cooling medium, preferably water, can flow, and at least one electron-optical component for beam guidance, preferably at least one magnetic coil.

[0043] Furthermore, a removable lining can be arranged on the inner wall of the radiant tube, which has a thermal conductivity λ greater than or equal to 50 W / (m · K), preferably greater than or equal to 300 W / (m · K) and which expands when heated in order to conform essentially to the actively cooled inner wall of the radiant tube.

[0044] For example, the beam tube of the beam guidance device can be permanently flanged to a coating chamber. Furthermore, a thin-walled tube, preferably made of copper, can be inserted through the front outlet of the tube into the chamber to serve as a lining. This lining can be easily replaced if it becomes dirty, allowing the entire beam tube optics to be permanently installed in the coating chamber and remain there. During operation, the lining heats up due to scattered electrons, expands slightly, and then fits snugly against the cooled wall of the beam tube, thus being effectively cooled itself. This ensures that even in the event of a malfunction, such as a magnetic lens failure, the energy of the electron beam is safely dissipated into the cooled wall without causing damage.

[0045] The emitter arrangement and beam guidance device described above can also be combined to form an axial electron gun.

[0046] In particular, the present invention provides an axial electron gun for vaporizing a coating material in a vacuum environment, comprising one of the emitter arrangements described above, and an actively cooled beam guidance device as described above.

[0047] In particular, the emitter arrangement can be combined with the beam guidance device in such a way that the accelerator anode of the emitter arrangement is in thermal contact with the beam guidance device and is at least partially actively cooled by it.

[0048] The emitter assembly, including the cathode block and accelerating anode, can be located outside the coating chamber at the rear of the electron gun. All components can be easily replaced and cleaned from there by loosening a few screws, which do not corrode due to the low operating temperatures.

[0049] Such an axial electron gun makes it possible, in particular, to generate an electron beam in which the power density of the electron beam on the material to be vaporized is in the range of 1 - 30 kW / cm². 2 preferably in a range of 10 - 20 kW / cm² 2 Typically, the area of ​​the burn spot on the coating material or in the processing zone is not less than 50 mm². 2 .

[0050] Using some or all of the embodiments of the present invention described above, a robust, maintenance-friendly electron gun with a simple design can be constructed, which exhibits a long service life of at least 50, preferably at least 100 hours, even when vaporizing large quantities of material, preferably more than 50 g / h, and particularly preferably more than 100 g / h. Furthermore, active cooling of the electron gun, both in the emitter area and in the beam guidance system, ensures high mechanical stability and intrinsic safety. 4. Description of the drawings

[0051] Certain aspects of the present invention are described below with reference to the attached drawings. These drawings show: Fig. 1 a schematic representation of an electron gun in Pierce configuration known from the prior art, Fig. 2 a technical representation of an actively cooled axial electron gun according to an embodiment of the present invention in longitudinal section, Fig. 3a a schematic representation of an emitter arrangement according to an embodiment of the present invention, also in longitudinal section in comparison to Fig. 2 rotated by 90°, Fig. 3b a further schematic representation of an emitter arrangement according to an embodiment of the present invention, also in longitudinal section in a section plane which, in comparison to the Fig. 3 is rotated by 90°, Fig. 4 a top view of a tungsten filament that can be used in an emitter arrangement and electron gun according to an embodiment of the present invention. 5. Detailed description of some exemplary implementations

[0052] The following section describes in detail some exemplary embodiments of the present invention using the example of a water-cooled axial electron gun. Various combinations of features are described with reference to some exemplary embodiments of the present invention. Naturally, not all features of the described embodiments need to be present to realize the present invention. Furthermore, the embodiments can be modified by combining certain features of one embodiment with one or more features of another embodiment – ​​provided this is technically compatible and practical – without deviating from the disclosure and scope of protection of the present invention as defined by the claims.

[0053] An electron gun according to an embodiment of the present invention is in Fig. Figure 2 shows a longitudinal section. The electron gun 10 with axial beam guidance has an actively cooled source section or emitter arrangement 11. The emitter arrangement 11 comprises a cathode block 20, which includes an emitter assembly that, in the embodiment shown, is configured as a Pierce emitter.

[0054] Furthermore, the emitter arrangement has an anode ring 15. In front of it is a cooled beam tube on which magnetic coils 18 are mounted for guiding, focusing and deflecting the electron beam.

[0055] The wall of the emitter assembly 11 and the cathode block 20 are actively cooled by good thermal coupling to a water-cooled mounting plate / heat sink 21, the heat sink being actively cooled by cooling channels 16. High-voltage electrical insulation with simultaneously high thermal conductivity is achieved by a highly thermally conductive insulator with a thermal conductivity of at least 20 W / m·K and an electrical resistance of at least 10 9 The insulator has a specific thermal conductivity of Ω·cm. In particular, the insulator can be made of carbon (e.g., diamond) or elements of its neighboring main groups, i.e., III-V compounds with a very large band gap of at least 4 eV, preferably 5 eV or more. Since the insulator must be machined, e.g., to cut threads, aluminum nitride (Al₂N₃), boron nitride (BN), or a mechanically machinable mixture of both, traded under the name Shapal, are preferably used.

[0056] However, these substances can also be embedded as thermally conductive fillers in an electrically insulating plastic, since the component remains cold at this point due to the cooling of the heat sink.

[0057] The jet tube can also include cooling water channels 16, which are supplied with cooling water via inlet and outlet nozzles 17. The accelerating anode 15 is designed as a ring and is pressed against the cooled housing of the jet tube by the emitter assembly, so that the anode ring is also well cooled.

[0058] A small aperture of 5 to a maximum of 8 mm in diameter allows the anode to differentially pump the emitter arrangement via a pump nozzle 13. A small turbomolecular pump with a preferably 80 1 / s pumping capacity can optionally be mounted on this nozzle, or a bypass to the coating chamber (not shown) can be provided to evacuate the emitter arrangement more quickly.

[0059] The electrical connection between the cathode and the high-voltage and filament power supply is made via a plug connection 14 with a securely sheathed, high-voltage insulated contact plug that can be attached from the outside.

[0060] The inner wall of the blast tube, which is permanently installed with the coating chamber, can be protected from contamination by a lining tube 19 with good thermal conductivity. The lining can be loosely inserted into the blast tube from the front. During operation, the lining expands and conforms tightly to the cooled wall of the blast tube. This ensures that the lining is also very well cooled and, even in the event of a malfunction, such as the failure of a magnetic coil 18, can safely dissipate the energy of the electron beam into the cooling water. The electron gun shown is therefore inherently safe by design.

[0061] Fig. 3a and Fig. Figure 3b shows two schematic longitudinal sections, rotated axially by 90°, through the cooled cathode block 20 with an emitter assembly 23-28. The emitter assembly sits on a water-cooled mounting plate / heat sink 21. The cooling lines are not shown here.

[0062] This is fixed to the emitter chamber from the rear with four screws and a vacuum sealing ring, and can be easily removed by loosening these screws. A block of highly thermally conductive ceramic is screwed onto the mounting plate 21, providing a flat contact surface and low thermal resistance. Preferably, mechanically machinable Al2N3-BN, trade name "Shapal", is used here.

[0063] Shapal is non-porous, non-outgassing, and vacuum-compatible. It possesses a high thermal conductivity of 90 W / m·K and is characterized by high mechanical strength and low thermal expansion. Furthermore, it is an excellent electrical insulator (>10). 12Ω cm, with high dielectric strength of 65 kV / mm and represents the electrical insulation between the high voltage of the emitter assembly 23 - 28 and the grounded mounting plate 21.

[0064] Two copper half-cylinders 23a and 23b are screwed onto the insulator 22 as the lower part of the emitter assembly. They are separated by a gap approximately 1 mm wide and two embedded electrical insulators 26. These are made of commercially available and therefore cost-effective industrial ceramics, such as Al₂O₃. The connectors for the high-voltage source and the filament power supply terminate in the two electrically insulated half-cylinders.

[0065] The upper part of the emitter assembly 23-28, which forms a so-called Pierce shield, sits on these half-cylinders. This part also comprises two halves 24a and 24b, which have a central gap and are insulated from each other by embedded ceramic pills 26. The Pierce shield is concave towards the center and also has a central through-hole into which positively charged ions from the cathode compartment are directed. These ions then collide with a ceramic pill 27 and are stopped there. This pill can also be made of commercially available ceramic, such as Al₂O₃, and has the same dimensions as the insulators 26. This ion sump serves to trap the ions and extends the lifetime of the emitter assembly. By simply rotating the ceramic cylinder, the entire outer surface can be used as an ion trap.

[0066] Arranged in the concave curvature of the Pierce shield, a heated tungsten filament 25 with a diameter of 10–20 mm, preferably 10–16 mm, serves as the actual electron emitter. This filament is designed as a flat spiral so that the electrons are emitted from a planar arrangement and in Fig. 4 shown.

[0067] The spiral is bifilar in design, meaning there is no tungsten ridge in the center that could be destroyed by ion bombardment. This allows ions accelerated against the beam direction to pass unimpeded through the filament plane into the ion pool below, where they are stopped.

[0068] For mounting the filament 25, each of the two halves of the Pierce shield has a bore for the legs of the filament and perpendicular to it clamping devices 28a, 28b for fixing.

[0069] The individual elements of the cathode block 21, 22, 23, 24 have smooth end faces and are firmly screwed together, ensuring good heat transfer. Since the components are actively cooled, thermal paste or vacuum grease can even be applied between the end faces to improve the surface thermal contact.

[0070] In the depictions of the Fig. 3a, Fig. 3b The screw connections of the cathode block components are not explicitly shown for clarity.

[0071] All parts of the cathode block are self-adjusting and remain cool during operation. Despite the filament heating power of approximately 200 W, the temperature of the Pierce shield 24 remains below 150°C. The remaining parts of the cathode block 22, 23 remain below 120°C, preferably below 100°C, due to cooling. This ensures they retain their shape, do not scale, and all screws can be easily opened for maintenance and filament changes.

[0072] The anode ring 15 serves as the inlet opening to the beam tube in front of the emitter. The diameter of the central aperture is approximately 50% of the filament diameter and is preferably in the range of 5–8 mm. The anode ring is inserted into a groove and, during assembly of the emitter assembly with the beam guidance device 12, is pressed firmly against the cooled wall of the beam tube. Due to the sputtering action of ions and the slow evaporation of W₂O₃ from the tungsten emitter, residues are deposited on the anode ring and surrounding walls over time. Therefore, the anode ring can be easily removed and cleaned. Reference symbol list: 10 Axial electron gun 11 Cooled source section / emitter arrangement of the electron gun 12 Cooled beam guidance device of the electron gun with beam tube and attached magnetic coils 13 Flange for vacuum pump (pump nozzle) 14 connectors for high-voltage and filament power supply 15 anode ring 16 water-flowing cooling channels 17 Cooling water connection 18 magnetic coils for beam guidance 19 Lining pipe (Cu) 20 cathode blocks 21 Water-cooled mounting plate / heat sink with cooling channels 22 Shapal Insulator 23, 23a, 23b Base part(s) of the cathode block with power leads (not shown) 24, 24a, 24b Pierce shield of the cathode block 25 Tungsten filament (flat spiral) 26 ceramic discs as spacers 27 Ceramic disc as ion sump 28a, 28b Clamping mechanism for the filament

Claims

[1] Emitter arrangement (11) for an electron gun (10), comprising: an actively cooled cathode block (20), and an accelerator anode (15), preferably ring-shaped; wherein the cathode block (20) comprises: a heat sink (21); an emitter assembly (23 - 28); and an insulator (22) which is arranged in a thermally conductive manner between the heat sink (21) and the emitter assembly (23 - 28), wherein the insulator (22) has a thermal conductivity λ greater than or equal to 20 W / (m · K), preferably greater than or equal to 50 W / (m · K) and more preferably greater than or equal to 90 W / (m · K). [2] Emitter arrangement (11) according to claim 1, wherein the insulator (22) is made of a highly thermally conductive ceramic or a plastic with a highly thermally conductive ceramic filler material, wherein the ceramic material preferably comprises a compound of elements of the III and V main groups, more preferably Al2N3 and / or BN. [3] Emitter arrangement (11) according to claim 1 or 2, where the insulator (22) has a resistivity ρ greater than or equal to 10 9 Ω · cm, preferably greater than or equal to 10 10 Ω · cm, preferably greater than or equal to 10 11 Ω · cm, and most preferably greater than or equal to 10 12 Ω · cm; wherein the insulator (22) has an electrical breakdown strength of greater than or equal to 40 kV / mm, preferably greater than or equal to 50 kV / mm and more preferably greater than or equal to 65 kV / mm. [4] Emitter arrangement (11) according to any one of the preceding claims, wherein the emitter arrangement (11) generates an electron beam with a power of 0.5 kW - 36 kW, preferably with a power of 1 - 15 kW; and / or wherein the emitter arrangement (11) generates an electron beam with an effective beam current of 100 mA - 1200 mA at an accelerating voltage of 5 - 30 kV, preferably of 6 - 12 kV. [5] Emitter arrangement (11) according to any one of the preceding claims, wherein the temperature of the emitter assembly (23 - 28), measured at the outer edge of the surface of the emitter assembly (23 - 28) facing the accelerator anode (15), is not greater than 200°C, preferably not greater than 175°C, and more preferably not greater than 150°C, and / or wherein the accelerator anode (15) is actively cooled, so that during operation of the emitter arrangement (11) the temperature of the accelerator anode (15), measured at the outer edge of the accelerator anode (15), is not greater than 200°C, preferably not greater than 175°C, and more preferably not greater than 150°C. [6] Emitter arrangement (11) according to any one of the preceding claims, wherein the cooling element (21) has at least one cooling channel (16) through which a cooling medium, preferably water, can flow; and / or wherein the heat sink (21) is made of a material, preferably copper or aluminium, which has a thermal conductivity λ greater than or equal to 200 W / (m · K). [7] Emitter arrangement (11) according to one of the preceding claims, wherein the emitter assembly (23 - 28) comprises two electrically isolated subunits (23a, 24a); (23b, 24b) whose surfaces facing the anode ring (15) form an at least partially concave depression into which a heating coil (25), preferably a tungsten filament, is inserted. [8] Emitter arrangement (11) according to the preceding claim 7, wherein the center of the heating coil (25) is recessed; and / or wherein the heating coil (25) is designed as a flat spiral so that the electrons are emitted from a planar arrangement; and / or wherein the heating coil has a heating power of greater than or equal to 150W, preferably greater than or equal to 200W. [9] Emitter arrangement (11) according to one of the preceding claims, wherein a central channel is arranged in the cathode block (20) which leads into an ion sump in which positive ions are stopped in a replaceable ion absorber (27), preferably a rotatable ceramic pill, which serves as sacrificial material. [10] Emitter arrangement (11) according to any of the preceding claims, wherein the accelerator anode (15) has an aperture with a mean diameter of 5 mm to 8 mm; and / or wherein the emitter arrangement (11) has a connection for a vacuum pump or a bypass; and / or wherein in the emitter arrangement (11) a background gas pressure of at most 5 · 10 -5 mbar predominates. [11] Actively cooled beam guidance device (12) for an electron gun (10) with a beam power in the range of 0.5 kW to 36 kW, comprising: a jet pipe having at least one cooling channel (16) through which cooling water can flow; and at least one electron-optical component (18) for beam guidance, preferably at least one magnetic coil. [12] Actively cooled beam guidance device (12) according to claim 11, wherein a removable lining (19) is arranged on the inner wall of the beam tube, which has a thermal conductivity λ greater than or equal to 50 W / (m · K), preferably greater than or equal to 300 W / (m · K) and which expands when heated in order to conform substantially to the actively cooled inner wall of the beam tube. [13] Axial electron gun (10) for vaporizing a coating material in a vacuum environment, comprising an emitter arrangement (11) according to any one of the preceding claims 1-9; and an actively cooled beam guidance device (12) according to one of the preceding claims 11 or 12. [14] Axial electron gun (10) according to claim 13, wherein the accelerator anode (15) of the emitter arrangement (11) is in thermal contact with the beam guidance device (12) and is at least partially actively cooled by it. [15] Axial electron gun according to claim 13 or 14, wherein the power density of the electron beam on the material to be vaporized is in a range of 1 - 30 kW / cm² 2 preferably in a range of 10 - 20 kW / cm² 2 lies.

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