Annular device for generating accelerated electrons

Abstract

The invention relates to an annular device for generating accelerated electrons, comprising an annular housing (101), which delimits an annular evacuable space (102a; 102b) and has an annular electron exit window (104); at least one first reservoir (121), which contains a working gas; at least one first inlet (120) for feeding the working gas from the first reservoir (121) into the annular evacuable space (102a; 102b); at least one first cathode and at least one first anode, between which a glow discharge plasma (106) can be generated in the annular evacuable space (102a) by means of a first applied electrical voltage. Ions from the glow discharge plasma (106) can be accelerated onto the surface (110) of an annular second cathode (107), and electrons emitted from the annular second cathode (107) can be accelerated toward the annular electron exit window (104) by means of a second electrical voltage applied between the annular second cathode (107) and an annular second anode (108). The housing (101) is the first cathode. The first anode comprises a number of wire-like electrodes (105), which extend completely or partly through the annular evacuable space (102a). A second reservoir (122) contains a hydrocarbon-containing compound, which can be admitted into the evacuable space (102a; 102b) through the at least one first inlet (120).

Description

[0001] Ring-shaped device for generating accelerated electrons

[0002] Description

[0003] The invention relates to an annular device for generating accelerated electrons. In particular, a device according to the invention can be used to impinge on bulk materials, strand materials, and fluids with accelerated electrons. The preferred field of application is the phytosanitary treatment of seeds against seed-borne pathogens, which are predominantly found in the seed coat. Other fields of application include the sterilization and modification of the near-surface layer of granules and powders, e.g., also of animal feed, herbs, and spices, the chemical surface activation of recycled materials, and the implementation of other radiation- and plasma-chemical processes.

[0004] Various methods and corresponding devices for applying accelerated electrons to bulk materials and strand materials are known in various designs - adapted to the bulk material or strand material to be treated.

[0005] For example, an electron field with opposing electron velocity components is generated in an evacuated chamber by arranging two electron accelerators opposite one another. The bulk material is guided through this field in free fall in an extended transparent stream (DD 291 702 A5). For electron treatment, the bulk material is introduced into the chamber via rotary valves and discharged again after the electron treatment process. The disadvantage of such devices, however, is the high equipment complexity for generating the electron field, since at least two electron accelerators with corresponding filament voltage supplies are required, as well as the high vacuum technology complexity.

[0006] It is also known to generate an electron field with opposing velocity components by magnetically deflecting the electron beam back onto the particle stream after it has passed through the stream of bulk particles. Devices of this type avoid the expense of a second electron accelerator. The disadvantage of this method, however, is that the relatively long path the electron beam travels in the process chamber requires a significantly higher vacuum, which requires even greater equipment complexity in terms of vacuum generation.

[0007] Methods and devices are also known that operate with two opposing electron accelerators, with the electrons exiting through a beam exit window at atmospheric pressure (DE 44 34 767 C 1). The bulk material is also guided through the electron field in free fall. This solution eliminates the effort required to evacuate the process chamber. However, the disadvantage of the high equipment complexity required for the use of at least two electron accelerators remains.

[0008] It is also known to subject powdered and granular materials to electrons at atmospheric pressure, using only an electron accelerator and carrying the particles to be irradiated in a gas stream through the electron field (WO 98 / 43274 A1). The gas stream containing the particles to be irradiated is guided through a rectangular channel sealed on one side by a 25 μm thick aluminum foil, into which the electrons penetrate after being discharged through a 13 μm thick titanium window foil and traversing the distance to the irradiation channel. Opposite the aluminum foil, the rectangular channel is formed by a flat plate made of a material with a high atomic number. After penetrating the channel cross-section, the electrons are backscattered to a certain extent by this plate.The backscattered electrons have a velocity component opposite to the original direction of incidence of the electrons and allow that the side of the particles facing away from the original direction of incidence of the electrons is also exposed to electron bombardment.

[0009] A disadvantage is that the intensity of the radiation from the backscattered electrons is significantly lower than the intensity of the radiation from the electrons directly emerging from the beam exit window, which leads to uneven irradiation of the individual particles. Another disadvantage is that the gas velocity required to carry the particles increases sharply with increasing mass-to-surface ratio of the transported particles. Thus, very high gas flow velocities would be required for larger-grained bulk materials—such as wheat or corn. At these high velocities, the energy doses transferable in the electron field would be limited to very small values, far too low for many applications.A further disadvantage of this known solution is that, after exiting the electron accelerator, the electrons must also pass through the aluminum foil sealing the rectangular channel before they reach the particles to be treated. This causes the electrons to suffer an additional, undesirable energy loss.

[0010] DE 199 42 142 A1 further describes a device in which bulk material is passed past an electron beam device in multiple free fall steps and subjected to accelerated electrons. Due to the multiple passes, combined with the intermittent mixing of the bulk material, the probability in this embodiment is very high that the particles of the bulk material will be exposed to accelerated electrons on all sides. However, the multiple passes require a significant amount of time to carry out the treatment process.

[0011] DE 10 2013 1 1 1 650 B3 and DE 10 2013 1 13 688 B3 disclose devices in which an electron beam source is ring-shaped such that electrons emitted and accelerated by a ring-shaped cathode exit from an electron exit window in the direction of the ring axis. The ring-shaped electron beam generator is arranged so that its ring axis is aligned as vertically as possible. Arranged above the ring-shaped electron beam generator is a device for separating bulk material particles, the bottom wall of which has at least one opening through which bulk material particles fall and from there through the ring formed by the electron beam generator. One advantage of such a ring-shaped device is that it is more compact than devices consisting of two planar beam sources.However, the disadvantage remains that the minimum speed at which the bulk particles are guided past an electron exit window is determined by the acceleration due to gravity and cannot be undercut. Therefore, such a device requires electron beam generators with relatively high power, which allow the required electron dose to be applied in the short time within which the bulk particles fly past an electron exit window. Another disadvantage is that the speed of the bulk particles constantly increases as they fly past the electron exit window, resulting in a bulk particle being exposed to a constantly decreasing electron density as it passes the electron exit window.A special feature of the annular electron beam generators described in DE 10 2013 1 1 1 650 B3 is that the beam electrons are not thermally emitted by heating the cathode ("hot cathode"), but are knocked out of it by ion impact ("cold cathode"). The ions required for this are generated by gas discharges in a plasma chamber, also annular, located between the annular cold cathode and the annular electron exit window. For reasons of high-voltage insulation, these must burn at particularly low pressures, which requires special discharge arrangements.

[0012] Furthermore, EP 3 590 125 B1 discloses annular electron beam generators with a cold cathode that utilize a wire anode arrangement for ion production. The annular plasma chamber is divided into ring segments by walls, and at least one wire-shaped anode extends through each ring segment to generate a plasma in the ring segment. EP 3 642 861 B1 utilizes this principle of plasma generation in individual segments to construct an electron beam generator in which the ring is incomplete, i.e., permanently has an open sector, or consists of two half-rings that can be separated and reassembled without breaking the vacuum.

[0013] The described segmentation of the plasma chamber is disadvantageous because the walls have the same electrical potential as the cathodes of the gas discharge (which, understandably and explicitly described in the exemplary embodiment, is identical to that of the housing and the electron exit window, i.e., the ground potential). As a result, the cathode drop of the discharge and a lower plasma density form in their vicinity, so that a lower ion current density can be extracted there than from the center of the ring segments and accelerated toward the cold cathode. This also makes it impossible to provide a uniform electron current density and irradiation intensity across the entire circumference of the ring.

[0014] Cold cathode electron guns have numerous advantages, which are explained in the documents cited above, but in practical use, especially in continuous operation, they prove to be problematic from the point of view of operational stability.

[0015] An important criterion for the operational stability of electron beam sources is the so-called dielectric strength. The observed frequency of high-voltage flashovers is typically used as a measure of the dielectric strength of electron sources. These flashovers not only interrupt beam generation but also wear out the source's internal components and stress the semiconductor electronics of the control and supply devices. Therefore, the flashover rate must be reduced to a tolerable level through time-consuming conditioning routines before the actual beam operation begins. This is further complicated by the high parasitic capacitance of the necessarily large-area cold cathodes, which, in the event of a flashover, can lead to RF oscillations and resulting AC stress and destructive overvoltages in the assembly system (high-voltage cables, connectors, and feedthroughs).Furthermore, it should be noted that the initial conditioning during beam operation is not permanently effective. The flashover rate then increases again, largely fueled by another mechanism: the deposition of insulating deposits at the critical cathode-insulator transition ("triple point"). These insulating edge layers next to the active emission zone are formed by ion impact in the center of the cold cathode, sputtering of aluminum atoms, and their backscattering and oxidation (by oxygen in the residual gas and adsorbed water films) to aluminum (hydr)oxide. Charge carriers can accumulate on these layers and generate voltage differences along the surface, which are occasionally equalized by creeping sparks. These are harmless in themselves, but act as ignition sources for high-voltage flashovers (high-current arc discharges) from the cathode to ground.These cause a roughening of the cathode and a further increase in the tendency to flashover with increasing operating time due to field emission from sharp-edged microstructures (such as "crater edges", peaks, splashed melt droplets).

[0016] The dose applied to the treated material is determined not only by the electron energy (which can be easily controlled by accelerating voltage) but also by their current density (which is subject to a certain degree of uncertainty). This uncertainty arises from the fact that the emission current density of the secondary electrons released by the ion bombardment of the cold cathode depends strongly on the chemical and morphological properties of the cathode surface. Depending on whether the surface is metallically bare or covered with a thin oxide layer, fewer or more secondary electrons are released per projectile ion. The ratio of the two species is referred to as Townsend's secondary electron coefficient and is usually abbreviated as "y" in the technical literature.It can change over time – as is well known from the literature – due to ion bombardment (and the resulting sputter removal of deposits and near-surface layers of the cathode), water desorption, and varying oxygen partial pressure (and the resulting controlled growth of dielectric compound layers on the cathode surface). Less extensively investigated and documented in the literature, but plausible, are the influences of surface roughness and crystallite structure, thus the semi-finished product quality and the aging state of the cold cathode over its service life.

[0017] However, the efficiency of beam generation depends on y—that is, how much electron current (out of the cathode) is generated by how much cathode current (supplied to the cathode by the high-voltage device). This ratio (and thus ultimately the beam current) is difficult to determine metrologically, since the cathode current (easily measurable in the high-voltage device) compensates not only for the amount of charge emitted by the negative electrons, but also, indistinguishably, for the amount of charge absorbed by the positive ions.

[0018] In summary, it can be stated that

[0019] 1) the beam current depends monotonically on the cathode current, but its exact value is unknown if the coefficient y is unknown and

[0020] 2) changes in the coefficient y that cannot be directly measured result in unnoticed changes in the beam current despite a constant cathode current and

[0021] 3) local variations of the coefficient y are directly translated into variations of the local electron current density, which cannot be determined either.

[0022] These are fundamental weaknesses of cold cathodes, which become increasingly apparent as the cathode area is scaled up.

[0023] Another serious problem is the tendency of the wire anode plasma, which produces the ions required to release the secondary electrons from the cathode, to localize. From a technological perspective, the goal is often to achieve the best possible (rotationally symmetric) homogeneity of the plasma density in order to achieve a homogeneous current density of the ions striking the cathode and thus also of the secondary electrons emitted by it along the circumference. However, at small discharge currents (such as those required to regulate small electron currents) and low pressures (which are conducive to stable high-voltage insulation), a wire anode discharge tends to no longer burn evenly across the entire circumference of the source, but only in the vicinity of a few wires. Accordingly, the ion and electron currents are then concentrated in this sector.In addition to a treatment dose that is unevenly distributed over the circumference of the source, this condition can also lead to destruction of the electron exit window due to local thermal overload of the titanium foil, since the beam current at its full programmed level hits a much smaller area of ​​the electron exit window.

[0024] Ultimately, it is precisely these disruptive effects that are to be counteracted by the above-cited documents EP 3 590 125 B1 and EP 3 642 861 B1 by segmenting the plasma space, but at the cost of the plasma, ion and electron current density, which is caused by the walls of the segments and is systematically uneven over the circumference, and thus also of the treatment dose.

[0025] The invention is therefore based on the technical problem of creating a device for generating accelerated electrons by means of which the disadvantages of the prior art can be overcome. In particular, the device according to the invention is intended to further develop annular electron beam sources such that even cold cathode sources remain permanently operationally stable, the material to be treated (bulk particles, strand material, or fluids) is exposed to an electron dose that is well-defined in time and across its entire circumference (which can be homogeneous or angle-dependently adjustable depending on the material to be treated and technological requirements) as it passes an electron exit window, dirt particles are kept away from the electron exit window, and the cost of cooling the system is reduced while still allowing a high throughput of material to be treated.

[0026] The solution to the technical problem is achieved by objects having the features of patent claims 1. Further advantageous embodiments of the invention are set out in the dependent patent claims.

[0027] A device according to the invention comprises an electron beam generator that is ring-shaped and in which the electrons emitted and accelerated by an annular cathode exit from an annular electron exit window in the direction of the ring axis. The electron exit window is thus at least a component of the annular inner wall of the annular electron beam generator and has the shape of a hollow cylinder.At this point, it should be expressly pointed out that the term "annular" in the sense of the invention is not limited to a circular ring for all annular devices, components and hollow cylinders described below, but that the term "annular" in the sense of the invention refers only to a loop-shaped, self-contained object, wherein the loop-shaped, self-contained object completely encloses a volume in its cross-section and wherein objects to be treated with accelerated electrons can be passed through this volume inside the ring. In a preferred embodiment of the invention, the cross-section of the volume completely enclosed by a ring or a hollow cylinder is circular, but can also have any other geometric shape in the broadest sense of the invention.

[0028] Such an annular electron beam generator comprises an annular housing which delimits an annular evacuable space and has an annular electron exit window; a first reservoir in which a working gas is contained; at least one first inlet for supplying the working gas from the first reservoir into the annular evacuable space; at least one first cathode and at least one first anode, between which a glow discharge plasma can be generated in the annular evacuable space by means of a first applied electrical voltage, wherein ions from the glow discharge plasma can be accelerated onto the surface of an annular second cathode and electrons emitted by the annular second cathode can be accelerated towards the annular electron exit window by means of a second electrical voltage applied between the annular second cathode and an annular second anode.In a device according to the invention, the housing is further configured as a first cathode, and the first anode comprises a number of wire-shaped electrodes extending completely or partially through the annular evacuable space. A device according to the invention further comprises a second reservoir containing a hydrocarbon-containing compound that can be introduced into the annular evacuable space through the at least one first inlet.

[0029] In one embodiment of the invention, the ring axis of the annular housing is oriented vertically or at an angle of up to 10° from the vertical, so that, for example, bulk material to be treated with accelerated electrons can fall from top to bottom through the annular opening of the annular housing. A protective grid can be arranged within the annular opening to mechanically protect the electron exit window from falling bulk material particles.

[0030] In a further embodiment, the device according to the invention comprises a first device with which a bottom-to-top flow of a gaseous medium (such as air) can be formed within the annular opening (i.e., within the volume enclosed by the electron exit window). This flow counteracts the free fall of the bulk particles and decelerates them as they fall. This increases the average residence time of the bulk particles in front of the electron exit window, allowing the use of a lower-power electron beam generator to achieve the same irradiation result as with prior art electron beam generators, in which bulk particles are guided past an electron exit window in free fall.

[0031] Such an upward flow of a gaseous medium can be formed, for example, if the gaseous medium is blown into the space between the electron exit window and the protective grid from below by means of the first device.

[0032] The invention is explained in more detail below using exemplary embodiments. The figures show:

[0033] Fig. 1 is a schematic and perspective sectional view of an annular device according to the invention;

[0034] Fig. 2 is a schematic representation of the annular device of Fig. 1 as a plan view;

[0035] Fig. 3 is a schematic sectional view of a first alternative device according to the invention;

[0036] Fig. 4 is a schematic sectional view of an alternative protective grille;

[0037] Fig. 5 is a schematic sectional view of a second alternative device according to the invention;

[0038] Fig. 6 is a schematic exploded view of a rotationally symmetrical element from Fig. 5. In Fig. 1 and Fig. 2, one and the same annular device 100 according to the invention is shown schematically, wherein the device 100 is shown in Fig. 1 as a perspective cross-sectional view and in Fig. 2 as a plan view. For better understanding, the terms "annular cylinder" and "annular disk" are defined at this point in relation to an annular object. If the inner radius of a circular ring is subtracted from its outer radius, a dimension results. If this dimension is smaller than the extension of the ring in the direction of its ring axis, the ring is designed as an annular cylinder. If, on the other hand, this dimension is greater than the extension of the ring in the direction of its ring axis, the ring is designed as an annular disk.

[0039] The annular device 100 initially comprises an annular housing 101, which, at least in one region, delimits an evacuable space that is divided into the evacuable spaces 102a and 102b. The evacuable space 102a is also referred to as the first evacuable space, and the evacuable space 102b as the second evacuable space. This evacuable space is also annular due to the shape of the housing and, in a preferred embodiment, has no walls dividing the evacuable space into ring segments, so that the evacuable space is continuous over the entire ring circumference. All components belonging to the device 100 and referred to as annular, described below, are radially symmetrical and have one and the same ring axis 103. On the inner side of the ring of the housing 101, the housing 101 is designed as an electron exit window 104 in the form of an annular cylinder, i.e.Viewed in the exit direction of the electrons, the electron exit window 104 has a surface perpendicular which is aligned towards the interior of the ring and, in the case of a circular ring cylinder as in the case of the electron exit window 104, towards the ring axis 103. A working gas contained in a first reservoir 121 is admitted into the evacuable space through at least one first inlet 120 in the housing 101, and a vacuum in the range from 0.1 Pa to 20 Pa, and preferably in the range from 1 Pa to 3 Pa, is maintained in the evacuable space by means of at least one pumping device (not shown in Fig. 1). In Fig. 1, the at least one first inlet 120 is illustrated such that it opens into the evacuable space 102a. Alternatively, and also preferably, the at least one first inlet opens into the evacuable space 102b.An annular device further comprises at least one first cathode and at least one first anode, between which a glow discharge plasma can be generated in the evacuable space by means of a first electrical voltage provided by a first power supply device. According to the invention, in the device 100 according to FIGS. 1 and 2, the housing 101 is designed as the first cathode, wherein the housing 101 designed as the first cathode can, for example, have the electronic ground potential of the device 100.

[0040] The first anode of the device 100, which is also referred to below as the electron beam generator 100, comprises a number of wire-shaped electrodes 105 that extend through the evacuable space 102a and, in a housing in the form of a circular ring, such as housing 101, are preferably arranged around the ring axis 103 on an identical radius and at the same distance from one another. The wire-shaped electrodes 105, which can have a slightly positive voltage potential in a range of +0.25 kV to +5.0 kV relative to the housing 101, are passed through the housing 101 in an electrically insulated manner. Due to the electrical voltage applied between the wire-shaped electrodes 105 and the first cathode, a plasma is formed in the evacuable space 102a. The evacuable space 102a is therefore also referred to below as the plasma space 102a.

[0041] An annular electron beam generator according to the invention further comprises at least one second cathode and at least one second anode, between which a second electrical voltage is connected by means of a second power supply device. In the electron beam generator 100, a cathode 107 serves as the second cathode, and a grid-shaped anode 108 serves as the second anode. Both cathode 107 and anode 108 are ring-shaped.

[0042] In an annular electron beam generator according to the invention, the second cathode represents the cathode for emitting secondary electrons, which are subsequently accelerated, and for this purpose has a high-voltage electrical potential, preferably in the range of -100 kV to -300 kV. The second cathode 107 is electrically insulated from the housing 101 by means of an insulator 109. In the electron beam generator 100 described in Fig. 1, the second anode 108 and the first cathode have the same electrical potential, which is embodied as an electrical ground potential. Alternatively, the second anode and the first cathode can also have different electrical potentials.

[0043] By applying a high-voltage potential in the range from -100 kV to -300 kV, positively charged ions are accelerated from the plasma 106 in the evacuable space 102a through the grid-shaped second anode 108 toward the second cathode 107. There, the ions impact a surface region 110 of the second cathode 107, whose surface is perpendicular to the ring interior of the housing, oriented toward the ring axis 103. Upon impact of the ions onto the surface region 110, the ions thus pass through a potential difference that largely corresponds to the acceleration voltage of the electron gun 100. Upon impact, the kinetic energy of the ions is released in a very thin surface layer of the cathode 107 in the surface region 110, which leads to the release of secondary electrons.At the aforementioned electrical voltages at the second cathode 107, the ratio between released electrons and impinging ions is on the order of up to ten, which makes this method of generating accelerated electrons very efficient. The resulting secondary electrons are strongly accelerated by the applied electric field and fly through the grid-like anode 108, which is designed in the form of a ring cylinder, and the plasma 106 in the space 102a. After passing through the electron exit window 104, which can be designed, for example, as a thin metal foil, the electrons penetrate into the volume 114 enclosed by the annular housing 101, in which a higher pressure can prevail than in the evacuable space and through which bulk material particles to be charged with electrons can be guided through the housing ring opening.Any material known from the prior art for an electron exit window, such as titanium, can be used as the material for the electron exit window 104. Furthermore, for the purpose of greater mechanical stability and cooling of the electron exit window 104, it is advantageous to provide it with a support grid, as is also known from the prior art.

[0044] It was previously described that when the ions impact the surface region 110 of the second cathode 107, secondary electrons are released. Unfortunately, in addition, material particles from the cathode are also sputtered off, from which, in a reactive process, electrically non-conductive oxides are formed. These oxides are deposited in the edge regions of the surface region 110 on the second cathode 107 and cause undesired areas there, which in turn leads to process instabilities. The device 100 according to the invention therefore also comprises a second reservoir 122, which contains a hydrocarbon-containing compound and which, like the working gas, is admitted into the evacuable space in a gaseous or vaporous state through the at least one first inlet 120. Preferably, for example, an alcohol can be admitted into the evacuable space as a hydrocarbon-containing compound.By admitting a hydrocarbon-containing compound into the evacuable space, carbon is also incorporated into the parasitic deposits on the second cathode 107 (as a result of cracking processes caused by the plasma and the beam electrons), which increases the electrical conductivity of the deposits, prevents surface sliding discharges and thus reduces the tendency to arc.

[0045] Since the hydrocarbon-containing compound is to be introduced into the evacuated space in gaseous or vaporous form, it is advantageous to use a highly volatile hydrocarbon-containing compound. Among the alcohol group, methanol, propanol, and especially ethanol are particularly suitable as hydrocarbon-containing compounds.

[0046] To admit the hydrocarbon-containing compound into the evacuable space, the hydrocarbon-containing compound can, for example, be present in liquid form in the second reservoir, and the working gas, which is also to be admitted into the evacuable space, can be passed through the liquid hydrocarbon-containing compound in the second reservoir and then admitted into the evacuable space through the first inlet 120. With such a procedure, vaporous components of the hydrocarbon-containing compound are introduced into the evacuable space with the working gas. Alternatively, the hydrocarbon-containing compound can also be admitted into the evacuable space using a separate mass flow controller.

[0047] Based on the volume introduced into the evacuable space through the first inlet, it is advantageous if the hydrocarbon-containing compound has a proportion of approximately 0.5 to 10 volume percent. Preferably, the hydrocarbon-containing compound has a proportion of approximately 2 to 6 volume percent. For the sake of completeness, it should be mentioned at this point that the annular electron beam generator 100 also has a cooling device, as is also known from the prior art in devices for generating accelerated electrons. For example, this device for cooling the electron beam generator 100 can comprise cooling channels that extend within the insulator 109 and through which a cooling medium flows.

[0048] The second anode 108, which in an annular electron beam generator is preferably designed as a grid-shaped annular cylinder segment and which represents the spatial boundary between the evacuable spaces 102a and 102b, fulfills three essential functions. Firstly, due to its voltage difference with respect to the second cathode 107, it accelerates the ions extracted from the plasma toward the second cathode. Secondly, it also accelerates the secondary electrons generated by the ion bombardment toward the electron exit window 104. Due to the fact that the grid structure of the second anode 108 is parallel to the secondary electron-emitting surface 110 of the second cathode 107, an electric field is created such that the trajectories of the accelerated secondary electrons also run largely radially and antiparallel to the trajectories of the ions releasing them.Furthermore, the second anode 108 shields the plasma from the voltage potential of the second cathode 107; thereby preventing too many electrons from drifting away from the wire-shaped electrodes 111 and thus contributing to maintaining the plasma 106 in the evacuable space 102a.

[0049] As previously explained, the wire-shaped electrodes 105, which together constitute the first anode, are guided in an electrically insulated manner through the walls of the housing 101 and, in one embodiment, extend parallel to the ring axis 103 and completely through the evacuable space 102a. In an alternative embodiment, at least some of the wire-shaped electrodes 105 penetrate only one wall of the housing 101 and end within the evacuable space 102a without penetrating the opposite wall. Such wire-shaped electrodes 105 are also referred to below as stub anodes. The use of stub anodes can positively influence the plasma formation in the evacuable space 102a, thereby expanding the application range of the device 100.In particular, the use of stub anodes reduces the tendency of the plasma to localize, and lower discharge currents, and thus also lower beam currents, can be controlled more stably.

[0050] In a further embodiment, each wire-shaped electrode 105 is assigned a separate power supply device, which provides the anode potential to the assigned wire-shaped electrode 105. Alternatively, a plurality of wire-shaped electrodes 105 can also be assigned a power supply device, which provides the same anode potential for all assigned wire-shaped electrodes 105. The electrodes assigned to a power supply device can, for example, be adjacent wire-shaped electrodes 105. Alternatively, a power supply can also be assigned wire-shaped electrodes 105 that result from a sequence, such as every second wire-shaped electrode 105, every third wire-shaped electrode 105, or every fourth wire-shaped electrode 105, etc.

[0051] In a preferred embodiment, the device 100 comprises a power supply device with four independently controllable channels for providing the anode potential for the first anode. Each of the four channels of the power supply device is assigned to a different 90° ring sector of the annular space 102a, with all wire-shaped electrodes 105 of a 90° ring sector being electrically conductively connected to the associated channel of the power supply device, so that all wire-shaped electrodes 105 of a 90° ring sector have the same anode potential. Alternatively, the power supply device with four channels can also be replaced by four separate power supplies or by two power supplies, each with two separately controllable channels. With such a circuit configuration of the wire-shaped electrodes 105, the four 90° ring sectors can be controlled separately for the purpose of plasma formation.The respective discharge current in the individual ring sectors and, as a result, also the electron current or the treatment dose in the corresponding ones.

[0052] The peripheral areas of the cathode or the atmosphere-side treatment chamber can then be controlled in such a way that a temporally and spatially well-defined pattern is achieved across the entire circumference of the electron exit window (which can be adjusted to be homogeneous or ring angle-dependent, depending on the material being treated and technological requirements). In a power supply unit with four channels, the individual channels of the power supply unit can either be operated together but with a freely programmable current setpoint, or they can be operated sequentially, whereby the order of operation, the duration of operation, and the temporal offset of the individual channels are freely programmable.

[0053] The four 90° ring sectors can, for example, all be controlled simultaneously. The local discharge current strength in the individual sectors can be selected to be the same or different, as required. However, it has proven problematic to supply all four 90° ring sectors simultaneously with the energy required to form a stable plasma. Therefore, the power supply device with the four channels is preferably set up in such a way that only one channel or a group of two or three channels is active at a time and provides the anode voltage for the wire-shaped electrodes 105 of the associated 90° ring sectors, and that the 90° ring sectors or groups are controlled one after the other. Neighboring 90° ring sectors do not necessarily have to be controlled directly one after the other. It can also be expedient to control opposite 90° ring sectors one after the other. This can then again be achieved with optional (ortechnology-compliant) with identical or different discharge currents.

[0054] In an advantageous embodiment, the discharge current intensity can be set equally in each 90° ring sector or group, which minimizes the fluctuation in the current demand from the associated high-voltage device. The regulation of an electron current density and treatment dose that is homogeneous in the time average over the circumference or that can vary depending on the angle can be achieved by means of an individual duty cycle for the 90° ring sectors or groups. For efficient plasma ignition and the most uniform current demand possible from the high-voltage device, it is also advantageous to provide a freely programmable time offset between the shutdown of the previous 90° ring sector(s) and the startup of the next 90° ring sector(s) (or group).

[0055] Fig. 3 shows a schematic sectional view of a first alternative device 300 according to the invention. The basis of the device 300 is an annular device, as described for Figs. 1 and 2. Therefore, the device 300 also comprises an annular housing 101, in which the ring axis 103 is oriented vertically or at an angle of up to 10° deviating from the vertical, so that, for example, bulk material to be treated with accelerated electrons can fall from top to bottom through the annular opening of the annular housing 101. A cylindrical protective grid 330 is arranged within the annular opening in front of the electron exit window 104, which protective grid mechanically protects the electron exit window from falling bulk material particles. The protective grid 330 can be made of a heat-resistant gauze material, for example.

[0056] By means of a first device 331, a flow 332 of a gaseous medium is formed, which is directed from bottom to top between the electron exit window 104 and the protective grid 330. On the one hand, this flow 332 cools the electron exit window 104, and on the other hand, the gaseous medium, which simultaneously also penetrates through the protective grid 330, slows the fall of the bulk material particles, which increases the average residence time of the bulk material particles in front of the electron exit window 104.

[0057] In addition, by additionally introducing the gaseous medium in the area between the electron exit window 104 and the protective grid 330, dirt particles which fall downwards with the bulk material particles and which are smaller than the openings of the protective grid 330 are kept away from the electron window 314, thereby reducing its contamination and thus increasing its service life.

[0058] In a further embodiment of the invention, the device 300 has at least one sensor, by means of which first actual values, which represent the falling velocity of the bulk material particles in front of the electron exit window 104, are recorded. Within a first evaluation device, these actual values ​​are compared with a first target value for the falling velocity of the bulk material particles, and a first comparison value is generated. The intensity of the flow 332 of the gaseous medium is regulated as a function of the first comparison value. The intensity of the flow 332 of the gaseous medium can be changed, for example, by changing the power of the first device 331 by means of an adjusting device. In this way, it can be ensured that the bulk material particles are exposed to a homogeneous and / or predetermined dose of accelerated electrons.It has already been described above that the protective grid in front of the electron exit window of a device according to the invention can consist, for example, of a heat-resistant gauze material. Such a gauze material typically comprises horizontally and vertically running metal threads or metal wires. Fig. 4 schematically shows an alternative protective grid 404 which, at least in the vertical region of the electron exit window 104, comprises only vertically running, metal first wires 430 that are stretched between an upper connecting ring 431 and a lower connecting ring 432, and wherein adjacent first wires 430 are spaced from one another by a distance that is smaller than the diameter of the bulk material particles. The second wires 430 thus also run parallel to the ring axis 103 of the ring-shaped electron beam generator.Horizontally extending wires of a protective grid in front of an electron exit window have the disadvantage that bulk material particles sliding past the protective grid from top to bottom introduce impact energy into the horizontally extending wires, which can lead to deformation or damage to the protective grid. A protective grid 404 according to Fig. 4, which has only vertically extending first wires 430, eliminates such a source of error. Such a protective grid 404 can be used in all embodiments of devices according to the invention described above and below.

[0059] In one embodiment, the metal first wires 430 are designed to be electrically insulated from one another, individually or in groups. By means of at least one measuring device, the electrical current flowing through a respective first wire 430 or a first group of first wires (430), or a second actual value representing this electrical current, can be detected and forwarded to a second evaluation device. This second actual value is compared within the second evaluation device with a second target value for the electrical current, resulting in a second comparison value. Depending on the second comparison value, the cathode current of the annular electron beam generator in the associated 90° ring segment can then be controlled by means of the discharge current intensity and / or the discharge duration.In this way, quality control can be carried out to determine whether the application of accelerated electrons to all ring segments is homogeneous, or according to a predetermined angular distribution over the circumference and with the required irradiation intensity. Depending on the second comparison value, the cathode current of the ring-shaped electron beam generator can be controlled by means of the discharge current intensity and / or the discharge duration in the individual 90° ring segments or groups. Through the direct and temporally and spatially resolved measurement of the electron current density in the treatment chamber, the uncertainty described above (due to an unknown or locally or temporally changing Townsend's secondary electron coefficient y) can be eliminated, and a technology-compliant treatment dose can be ensured.

[0060] In Fig. 5, a second alternative device 500 according to the invention is shown schematically in section, which initially has all the elements and features of the device 300 from Fig. 3. In addition, the device 500 comprises a rotationally symmetrical element 516, whose axis of rotation is identical to the ring axis 103 of the annular device 100 and the annular device 300. The rotationally symmetrical element 516 is shown schematically in Fig. 6 in somewhat more detail in an exploded view.

[0061] The rotationally symmetrical element 516 initially has a base body 620 in the form of a hollow cylinder, wherein the outer surface of the hollow cylinder consists of metal second wires 621, which are stretched between an upper connection element 622 and a lower connection element 623 and which run parallel to the ring axis 103 of the ring-shaped electron beam generator. Adjacent second wires 621 are each spaced apart by a distance that is smaller than the diameter of the bulk material particles that fall through the ring opening, so that no bulk material particles can enter the interior of the base body 620. The upper connection element 622 and the lower connection element 623 can, for example, be disk-shaped or ring-shaped.The rotationally symmetrical element 516 further comprises an upper closure element 624 and a lower closure element 625, which can both be conical, for example, and in which the conical outer surface is preferably completely closed. Alternatively, the two closure elements 624, 625 can also have a different shape that promotes the flow of the gaseous medium. In one embodiment, the rotationally symmetrical element 516 is arranged within the annular electron beam generator and dimensioned such that the metallic second wires 621 extend at least over the edges of the electron exit window 104.

[0062] Such a rotationally symmetric element 516 essentially achieves two positive effects. Firstly, the bulk material particles are guided into an annular gap between the protective grid 104 and the base body 620 of the rotationally symmetric element 516, forming a thin annular curtain of bulk material particles and guiding them past the electron exit window 104, resulting in a favorable result in terms of exposing the bulk material particles to accelerated electrons. Secondly, the bulk material particles can also be exposed to the rear side of the primary electrons, which, from the opposite side of the electron exit window, succeed in penetrating the curtain of bulk material particles and the not completely closed base body 620 of the rotationally symmetric element 516, further improving the result of exposing the bulk material particles to accelerated electrons.Such a rotationally symmetrical element 516, as described here only as an example for device 500, can alternatively also be used in all other embodiments of devices according to the invention.

Claims

Patent claims 1. Annular device for generating accelerated electrons, comprising an annular housing (101) which defines an annular evacuable space (102a; 102b) and has an annular electron exit window (104); at least one first reservoir (121) which contains a working gas; at least one first inlet (120) for supplying the working gas from the first reservoir (121) into the annular evacuable space (102a; 102b);at least one first cathode and at least one first anode, between which a glow discharge plasma (106) can be generated in the annular evacuable space (102a) by means of a first applied electrical voltage, wherein ions from the glow discharge plasma (106) can be accelerated onto the surface (1 10) of an annular second cathode (107) and electrons emitted from the annular second cathode (107) can be accelerated in the direction of an annular electron exit window (104) by means of a second electrical voltage applied between the annular second cathode (107) and an annular second anode (108), characterized in that the housing (101 ) is designed as the first cathode;that the first anode comprises a number of wire-shaped electrodes (105) which extend completely or partially through the annular evacuable space (102a), wherein a hydrocarbon-containing compound is contained in a second reservoir (122) which can be admitted into the evacuable space (102a; 102b) through the at least one first inlet (120).

2. Device according to claim 1, characterized in that the wire-shaped electrodes (105) are arranged in a ring around the ring axis (103) of the ring-shaped housing (101) within the annular evacuatable space (102a) and run parallel to the ring axis (103).

3. Device according to claim 1 or 2, characterized in that the ring axis (103) of the annular housing (101) is aligned vertically or at an angle of up to 10° from the vertical.

4. Device according to one of the preceding claims, characterized in that a cylindrical protective grid (330; 404) is provided in front of the electron exit window. (104) is ordered. Device according to claim 4, characterized by a protective grid (404) which, at least in the area in front of the electron exit window (104), comprises only vertically extending first wires (430). Device according to claim 5, characterized in that the vertically extending first wires (430) are individually or in groups electrically insulated from one another; a second actual value for the electric current flowing through one of the vertically extending first wires (430) or a group of first wires (430) of the protective grid (404) can be detected by means of at least one measuring device; the second actual value can be compared with a second setpoint value for the electric current by means of a second evaluation device, and a second comparison value can be generated; the cathode current of the ring-shaped electron beam generator in the associated 90° ring segment can be controlled depending on the second comparison value.A device according to any one of claims 3 to 6, characterized by a first device (331) by means of which an upward flow (332) of a gaseous medium can be generated within the annular opening of the annular housing (101). A device according to claim 7, characterized by at least one sensor by means of which a first actual value, representing the falling velocity of bulk material particles to be treated with accelerated electrons in front of the electron exit window (104), can be detected; a first evaluation device by means of which the first actual value can be compared with a first target value for the falling velocity of the bulk material particles and a first comparison value can be generated; and an adjustment device by means of which the power of the first device (331) can be controlled as a function of the first comparison value.Device according to one of claims 3 to 8, characterized by a rotationally symmetric device (516) whose axis of rotation is identical to the ring axis (103), comprising a base body (620) in the form of a hollow cylinder, wherein the outer surface of the hollow cylinder consists of metallic second wires (621) running parallel to the ring axis (103).

0. Device according to one of the preceding claims, characterized by a power supply unit with four independently controllable channels for providing the anode potential for the first anode, wherein each of the four channels of the power supply unit is assigned to a different 90° ring sector of the annular space 102a and wherein all wire-shaped electrodes (105) of a 90° ring sector are electrically conductively connected to the associated channel of the power supply unit, such that all wire-shaped electrodes (105) of a 90° ring sector have one and the same anode potential.

1. Device according to claim 10, characterized in that the channels of the power supply unit can be operated together but with a freely programmable current setpoint. 2.Device according to claim 10, characterized in that the channels of the power supply device can be operated successively but with freely programmable sequence, duration and programmable time offset.

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