IL270807B2

IL270807B2 - Apparatus for generating accelerated electrons

Info

Publication number: IL270807B2
Application number: IL270807A
Authority: IL
Original assignee: Fraunhofer Ges Forschung
Priority date: 2017-06-23
Filing date: 2018-06-22
Publication date: 2023-09-01
Also published as: WO2018234529A1; EP3642861A1; IL270807B1; IL270807A; PL3642861T3; DE102017113979A1; EP3642861B1

Description

Apparatus for generating accelerated electrons Field of the Invention The invention relates to a device for generating accelerated electrons. A device according to the invention can advantageously be used when applying accelerated electrons to strand-shaped substrates, molded parts, and fluids.

Prior Art Electron-beam technology has been used for several decades on an industrial scale for chemical material modification and for disinfection and/or sterilization of surfaces. The treatment of products can be performed at atmospheric pressure in an economically advantageous manner, for which purpose the electrons have to be initially released in vacuum, subsequently accelerated, and finally decoupled through a beam exit window, usually a thin metal foil, into the treatment zone. To penetrate sufficiently robust electron exit windows usable on a large industrial scale, and also for securing a sufficient treatment depth in the product, acceleration voltages >100 kV are typically required.Various methods and beam sources are well-established for a boundary layer treatment of flat products, such as plates and strips, while the treatment on all sides of molded bodies, bulk goods, and fluids still causes problems. A uniform application of electrons on all sides to curved surfaces is thus geometrically problematic because of shading effects, variable absorption of electron energy on the gas route, and dose inhomogeneities because of different projection ratios.A product treatment on all sides is only possible in a cumbersome manner, by using additional units, or with a high apparatus and/or technological expenditure using the already existing source systems, for example axial radiators having a rapid deflection unit or band radiators having an elongated cathode, of which both embodiments are operated using a heated thermionic cathode. Electron beam sources based on thermionic emitters are additionally mechanically complicated, difficult to scale, and require complex high-voltage supplies and high vacuum systems. In the event of damage to the beam exit window with collapse of the vacuum resulting therefrom, irreversible damage of the cathode system occurs and thus there is a high repair expenditure.

A device is disclosed in DE 199 42 142 A1, in which bulk material is guided past an electron-beam unit multiple times in free fall and subjected to accelerated electrons. Because of the multiple passes, in conjunction with thorough mixing of the bulk material in the meantime, the probability is very high in this embodiment that the particles of the bulk material will be subjected on all sides to accelerated electrons. However, the multiple passes require a high time expenditure when carrying out the treatment process. It is additionally disadvantageous in this case that the device is unsuitable for the treatment of larger molded parts.Another solution is specified in DE 10 2006 012 666 A1, which comprises three axial radiators having associated deflection controller and three also associated electron exit windows. The three electron exit windows are arranged in such a way that they enclose the entirety of a triangular free space. If a substrate is guided through this free space, accelerated electrons can be applied thereto in the entirety of its cross section in one treatment pass. However, if the substrate does not have the same triangular cross section as the free space enclosed by the three electron exit windows, the resulting dose distribution of the application of accelerated electrons on the surface of the substrate will be inhomogeneous. The apparatus expenditure in this embodiment is additionally very high, as a result of which this solution too is very price-intensive.A device is known from WO 2007/107331 A1, in which only two flat beam generators are required, between which a molded part is moved through for the purpose of sterilizing its surface, and accelerated electrons are applied thereto during this. This device additionally comprises multiple reflectors made of gold, by means of which edge beams emitted from the flat beam generators are reflected on surface regions of the molded part which are not located in the direct area of action of the flat beam generators. Since the reflectors known from this document consist of pure gold, such devices too are very price-intensive and thus impair the cost-effectiveness thereof. Since reflected electrons have a lower energy than non-reflected electrons, only an inhomogeneous introduction of energy into a substrate is also possible using this device.A ring-shaped device for generating accelerated electrons is disclosed in DE 10 2013 111 650 B3, in which all essential components, for example cathode, anode, and electron exit window, are formed ring-shaped, so that a ring-shaped electron-beam can be formed by means of such a device, in which the accelerated electrons move toward the ring interior. By means of such a device, for example strand-shaped substrates which are moved through the ring opening of the device can have accelerated electrons applied thereto comprehensively with respect to the substrate cross section. A device known from DE 10 2013 111 650 B3 typically has a circular ring shape, but can also be formed having any arbitrary other ring shape. In many applications, it is advantageous if the same energy dose is applied as far as possible to all surface regions of a substrate. In the known devices, this can be implemented by adapting the ring cross section to the strand cross section of the strand-shaped substrate to be irradiated when producing the ring-shaped radiation source. This has the disadvantageous effect that a ring-shaped radiation source, once manufactured, is only optimally suitable for the usage of substrates having one single cross-sectional shape. Moreover, accelerated electrons can only be applied to substrates which fit completely through the ring interior of the device by means of such a device. If only the beginning and end of a substrate have a larger cross section than the ring interior of the device, such a substrate cannot be processed by means of the device.

Summary of the Invention The invention is therefore based on the technical problem of providing a device for generating accelerated electrons, by means of which the disadvantages of the prior art can be overcome. In particular, using the device, the most uniform possible electron density is to be able to be applied to substrates having a non-rotationally symmetrical substrate cross section with respect to the substrate surface.The solution to the technical problem results by way of subject matter having the features of claim 1. Further advantageous designs of the invention result from the dependent claims.One feature of a device according to the invention is that it is formed ring-shaped, wherein the ring is not completely closed, however, and the electrons can be accelerated in the direction of the ring interior. A device according to the invention thus has the form of a ring segment, wherein the ring segment is formed having a ring angle of at least 45° and less than 360°. In principle, it is also possible to form the housing of a device according to the invention having a ring angle less than 45°. However, such embodiments hardly have any perceptible advantages over known surface radiators or line radiators. It is to be expressly noted at this point that the term "ring-shaped" in the meaning of the invention is not only limited to a ring in circular form in all ring-shaped devices and components described hereafter. The cross section of the free space enclosed by the ring is formed circular in one preferred embodiment of the invention, but can also have any other geometrical form in the broadest meaning of the invention.

Brief Description of the Drawings The invention is explained in greater detail hereafter on the basis of an exemplary embodiment. In the figures:Figure 1 shows a schematic and perspective cross-sectional illustration of a device according to the invention;Figure 2 shows a schematic illustration of a top view of the device from Figure 1;Figure 3 shows a schematic illustration of a top view of two alternative devicesaccording to the invention.

Claims

CLAIMS:

1. A device for generating accelerated electrons, comprising a housing, which delimits an evacuable space and comprises an electron exit window; an inlet for the supply of a working gas into the evacuable space; 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 applicable electrical voltage, wherein ions from the glow discharge plasma can be accelerated toward the surface of a second cathode and electrons which can be emitted by the second cathode can be accelerated in the direction of the electron exit window by means of a second electrical voltage applicable between the second cathode and a second anode, characterizedin that the housing, the second cathode, and the electron exit window are formed as a non-closed ring having a ring angle of at least 45°, wherein the surface perpendicular lines of the electron exit window and of the surface region of the second cathode, from which electrons can be emitted, are oriented toward the interior of the ring, wherein the first anode comprises a number of wire-shaped electrodes, which extend through the space, wherein the space is divided by means of walls into partial segments, wherein each partial segment comprises at least one wire-shaped electrode, which extends through the partial segment, and a separate power supply unit is associated with each partial segment, by means of which the strength of the electric current which flows through the at least one electrode of a respective partial segment is settable.

2. The device as claimed in claim 1 , characterizedin that the walls consist of an electrically conductive material.

3. The device as claimed in claim 2 , characterizedin that the walls have the same electric potential as the housing.

4. The device as claimed in claim 3 , characterizedin that the walls have electric ground potential.

5. The device as claimed in claim 1 , characterizedin that the housing and the first cathode have the same electric potential.

6. The device as claimed in claim 1 , characterizedin that the housing and the second anode have the same electric voltage potential.

7. The device as claimed in claim 1 , characterizedin that the second anode is formed as grid-shaped ring cylinder segment.

8. The device as claimed in any one of claims 1 to 7, characterized in that thehousing is formed having a ring angle of 180°. 5 9.The device as claimed in any one of claims 1 to 7 , characterized in that thehousing is formed having a ring angle of 270°. For the Applicants, WOLFF, BREGMAN AND GOLLER