Hollow cathode system for generating plasma and method of operating such a hollow cathode system

Abstract

The present invention relates to a hollow cathode system for generating plasma and a method for operating such a hollow cathode system, using an anode arrangement (13), a power supply (14) for supplying a voltage connected between the cathode capillaries (11a; 11b) and the anode arrangement (13), at least one gas reservoir (15) for supplying gas through the cathode capillaries (11a; 11b), using at least two mutually conductively connected cathode capillaries (11a; 11b), each of which is associated with a separate actuator (17a; 17b) that is used to adjust the amount of gas flowing through the cathode capillary (11a; 11b) associated with the respective actuator (17a; 17b).

Description

[Technical Field]

[0001] The present invention relates to a hollow cathode system for generating plasma for use in, for example, coating or processing a substrate surface under vacuum conditions, and to a method for operating such a hollow cathode system. [Background technology]

[0002] Hollow cathode plasma sources are used for a variety of tasks, such as plasma activation in PVD processes, excitation in PECVD processes, layer removal, cleaning, or physicochemical modification of surfaces, arc deposition, or as a heating source. The hollow cathode discharge's operating principle is particularly efficient plasma excitation between inclined cathode surfaces, with a working gas flowing through the interspace between the cathode surfaces (DE 102010011592 A1). Ions leaving the plasma region collide with the cathode's inner wall, providing electrons for the discharge via secondary electron emission (hollow cathode glow discharge) or thermionic emission (hollow cathode arc discharge), which are subject to various wear mechanisms. Ion bombardment leads to continuous sputtering of the hollow cathode in both discharge types (sputtering action). In the case of arc discharges, where hollow cathodes are typically tubular, high operating temperatures lead to increased sputtering rates, evaporation, recrystallization, and embrittlement of materials, as well as chemically assisted damage during reactive processes. At the same time, however, the ignition phase is particularly abrasive, since low-temperature arc spraying of materials often occurs here. Therefore, the lifetime of such plasma sources is only a few hours (depending on the operating characteristics and process conditions). This is far too short for the continuous industrial operation of one or even two weeks. Generally, a short cathode lifetime means a lot of lost time, since replacing worn parts requires interrupting the process and venting the process chamber (contaminating the process environment), which in turn requires subsequent readjustments. Storing multiple plasma sources and isolating them from the process chamber using vacuum technology via slide valves can be extremely time-consuming and expensive, and therefore not an economical option.

[0003] In addition to wear or lifespan problems, scaling up the plasma power is also a further problem. The discharge current in hollow cathode arc discharges is limited by the maximum achievable emission current density of the hollow cathode material before it reaches its melting temperature, as well as by the limited emission area (the discharge is concentrated in the so-called active region, i.e., in a specific axial region of the hollow cathode where the working gas pressure and the free path length of the plasma electrons are well matched to each other). Therefore, a significant increase in the discharge power cannot generally be achieved by increasing the load of the hollow cathode source, but can only be achieved by implementing multiple plasma sources operated in parallel, which is costly.

[0004] German Patent Application Publication No. 102006027853 discloses a hollow cathode system in which the cathode capillary tube is surrounded, at least at the end of the gas outlet opening, by an annular anode and an annular magnet coil. This hollow cathode system achieves higher plasma intensities than conventional hollow cathode plasma sources. International Publication No. 2013 / 091927 discloses a plasma source including two hollow cathodes, whose outlet openings face each other. A power supply that supplies an AC voltage is connected between the two hollow cathodes, so that the two hollow cathodes alternately function as cathodes and anodes in a hollow cathode arc discharge. This plasma source also generates a more intense plasma between the two hollow cathodes than a plasma source with only one hollow cathode. However, even in the two hollow cathode systems described above, the operating time is limited by the life of the cathode tubules.

[0005] A third problem with hollow cathode systems is the high material cost for wear parts: the hollow cathode, which must be replaced frequently, is always replaced in its entirety, even though wear is essentially concentrated in the active area.

[0006] The technical problem underlying the present invention is therefore to create a hollow cathode system for generating plasma and a method for operating such a hollow cathode system, which are able to overcome the drawbacks of the prior art. In particular, it is desired that the hollow cathode system according to the invention and the method according to the invention make it possible to enable a longer operating duration compared to the prior art. Furthermore, it is desired that the hollow cathode system according to the invention and the method according to the invention make it possible to vary the intensity of the plasma generated by the hollow cathode system according to the invention.

[0007] The solution to this technical problem is achieved by the subject matter with the features of claims 1 and 6. Further advantageous embodiments of the invention result from the dependent claims.

[0008] The hollow cathode system according to the present invention for generating plasma belongs to the category of devices in which a voltage is applied between the cathode capillaries and the anode device using a power supply. At the same time, when a working gas provided in a first gas reservoir flows through the cathode capillaries, an arc discharge can be formed between the cathode capillaries and the anode device in the vacuum chamber. The hollow cathode system according to the present invention is characterized in that it has at least two cathode capillaries that are electrically conductively connected to each other. Preferably, the cathode capillaries have a circular inner cross section. However, the inner cross section of the cathode capillaries in the hollow cathode system according to the present invention can alternatively have any other geometric shape. The conductive contact between the individual cathode capillaries can be formed, for example, using contact elements or, if the cathode capillaries are arranged adjacent to each other, by contacts. Therefore, all cathode capillaries in the hollow cathode system according to the present invention always have the same electrical potential. Furthermore, in the hollow cathode system according to the present invention, each cathode capillary is associated with a separate actuator, which can be used to adjust the amount and / or type of gas provided in the first gas storage unit that flows through the cathode capillary associated with the actuator.

[0009] A separate actuator for adjusting the amount of gas flowing through the cathode capillaries can be assigned to each cathode capillary, and each cathode capillary can separately ignite a hollow cathode arc discharge toward the anode device. Here, each cathode capillary of the hollow cathode system according to the present invention is assigned the same anode device for generating the hollow cathode arc discharge. It is known from the prior art that the plasma shape can be shaped by arranging multiple anode elements in a vacuum chamber. Therefore, in one embodiment, the anode device of the hollow cathode system according to the present invention can include multiple anode elements. In another embodiment, the element of the anode device is annular, surrounding all of the cathode capillaries at least on the side of the cathode capillary gas outlet opening.

[0010] The prior art generally knows the use of auxiliary devices for igniting hollow cathodes, such as heating coils wound around the hollow cathodes and connected to an associated power supply for supplying a heating voltage. Such auxiliary devices may also include magnetic field coils or permanent magnets for generating a magnetic field within or surrounding the hollow cathode, or a device for generating a high-voltage pulse between the hollow cathode and the anode device. Each cathode capillary of the hollow cathode system according to the invention may also be associated with such an auxiliary device for igniting an arc discharge. Any auxiliary devices used in the prior art for igniting hollow cathode arc discharges may be used.

[0011] As already explained, in the hollow cathode system according to the present invention, a separate arc discharge can be ignited and maintained starting from each cathode capillary, and thus a plasma can also be formed using each cathode capillary, with all plasmas formed using each individual cathode capillary passing through the same volume as far as possible. Summary of the Invention [Means for solving the problem]

[0012] Thus, in one embodiment, the tube axes of at least two cathode capillaries are oriented parallel to each other or have an angle of up to 5° with respect to each other, and gas flows from the gas reservoir through the at least two cathode capillaries in the same gas flow direction.

[0013] In order that the plasma generated with at least two cathode capillaries passes through as much as possible the same volume, it is also advantageous if adjacent cathode capillaries have a distance from each other of at most 20 mm.

[0014] A method according to the present invention for operating a hollow cathode system using an anode arrangement, a power supply connected between the cathode capillary and the anode arrangement for supplying a voltage, and at least one first gas reservoir for supplying gas to be passed through the cathode capillary is characterized in that it uses at least two cathode capillaries electrically conductively connected to each other, each cathode capillary being associated with a separate actuator, and the actuators are used to adjust the amount and / or type of gas passing through the cathode capillary associated with the respective actuator.

[0015] The hollow cathode system according to the present invention can operate in essentially two modes. In the first operating mode, an arc discharge is ignited using at least one first cathode capillary and maintained, for example, until the end of the life of the at least one first cathode capillary. To this end, at least the first cathode capillary uses a first actuator to adjust the amount of first gas flowing through the first cathode capillary, the amount of first gas being suitable for igniting and maintaining an arc discharge between the first cathode capillary and the anode device. When at least one first cathode capillary is worn or has reached the end of its life, the arc discharge from the first cathode capillary is extinguished, and subsequently, an arc discharge is ignited starting from at least one second cathode capillary. In this way, the operating duration of the hollow cathode system according to the present invention can be extended compared to the prior art, in which the vacuum chamber must be opened and the hollow cathode replaced after it wears out. In the previously described approach, an arc discharge is ignited in the cathode tube once and maintained for the duration of the cathode tube's operating time. Alternatively, it is also possible to activate the participating cathode tubes alternately and sequentially in partial cycles over their lifespan, so that all participating cathode tubes always have approximately the same state of wear, which is advantageous for maintaining uniform process conditions.

[0016] In the second operating mode of the hollow cathode system according to the present invention, the main focus is not on extending its operating duration, but on changing the intensity of the plasma generated by the hollow cathode system. As already explained, the plasma of each cathode tube of the hollow cathode system according to the present invention passes through substantially the same volume in the vacuum chamber. By additionally activating a second cathode tube when at least one arc discharge is already burning through a first cathode tube, or by deactivating a second cathode tube when an arc discharge is already burning through at least one first and one second cathode tube, the intensity of the plasma in the volume through which the plasma passes can be changed. Thus, in the second operating mode, arc discharges toward the anode device are maintained simultaneously through at least two cathode tubes, at least temporarily, which allows for the formation of a more intense plasma than would be possible if an arc discharge were burning through only one cathode tube.

[0017] The present invention will be explained in more detail below based on examples. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of a hollow cathode system according to the present invention. [Figure 2a] FIG. 1 is a schematic cross-sectional view of a first alternative cathode capillary configuration. [Figure 2b] FIG. 10 is another schematic cross-sectional view of a first alternative cathode capillary configuration. [Figure 3] FIG. 10 is a schematic cross-sectional view of a second alternative cathode capillary configuration. [Figure 4] FIG. 10 is a schematic cross-sectional view of a third alternative cathode capillary configuration. [Figure 5] FIG. 10 is a schematic cross-sectional view of a fourth alternative cathode capillary configuration. DETAILED DESCRIPTION OF THE INVENTION

[0019] FIG. 1 shows a schematic representation of a hollow cathode system 10 according to the present invention. The hollow cathode system 10 includes a first cathode capillary tube 11a and a second cathode capillary tube 11b, which are spaced apart by a maximum of 20 mm. The tube axes 12a and 12b of the two cathode capillaries 11a and 11b, respectively, are oriented parallel to one another. The hollow cathode system 10 also includes an anode device 13 and a power supply 14, which applies a voltage between the first cathode capillary tube 11a and / or the second cathode capillary tube 11b and the anode device 13 to generate an arc discharge. The two cathode capillaries 11a and 11b and the anode device 13 are located in a vacuum chamber, which is not shown in FIG. 1 for clarity.

[0020] During operation of the hollow cathode system 10, working gas flows in the same direction through the first cathode capillary 11a and / or the second cathode capillary. The working gas is provided in a first gas reservoir 15 and is conducted from the reservoir to the cathode capillaries 11a and 11b by a gas line 16. A first actuator 17a is associated with the first cathode capillary 11a, and a second actuator 17b is associated with the second cathode capillary 11b. The actuators 17a and 17b can be used to separately adjust the amount of gas flowing through the cathode capillary associated with each actuator. The two cathode capillaries 11a and 11b are electrically conductively connected to each other using a contact element 18 and therefore always have the same potential. The contact element 18 can be formed, for example, as a socket element made of an electrically conductive material into which the cathode capillaries 11a and 11b are screwed. If the two cathode capillaries 11 a and 11 b are arranged closely next to each other so that at least one continuous electrical contact is formed between them, the contact element 18 can be omitted. Therefore, by using the two actuators 17 a and 17 b, the hollow cathode system 10 can generate arc discharges starting from each of the two cathode capillaries 11 a and 11 b and directed separately toward the anode device 13.

[0021] In a first variant of the method, the first actuator 17a is used to adjust the amount of gas flowing through the first cathode capillary 11a, which is suitable for forming an arc discharge between the first cathode capillary 11a and the anode device 13. This ignites and maintains an arc discharge between the first cathode capillary 11a and the anode device 13. The cathode capillary involved in forming the arc discharge is hereinafter also referred to as the active cathode capillary. Therefore, as described above, when an arc discharge is formed from the first cathode capillary 11a to the anode device 13, initially only the cathode capillary 11a is the active cathode capillary, while the cathode capillary 11b is inactive. This allows one or more substrates placed in the vacuum chamber to be processed in conjunction with the plasma generated by the first cathode capillary 11a. When the life or operating time of the first cathode capillary 11a has expired, the arc discharge between the first cathode capillary 11a and the anode device 13 is first extinguished. Subsequently, the second actuator 17b is used to adjust the amount of gas flowing through the second cathode capillary 11b, which is suitable for forming an arc discharge between the second cathode capillary 11b and the anode device 13, to ignite and maintain the corresponding arc discharge. Thus, the processing of one or more substrates in the vacuum chamber can continue in conjunction with the plasma generated using the second cathode capillary 11b. In this way, the operating time of the hollow cathode system can be extended compared to the prior art without the need to open the vacuum chamber. Alternatively, the cathode capillaries 11a and 11b can be activated alternately and sequentially in partial cycles so that the cathode capillaries 11a and 11b always have approximately the same wear state. Preferably, the second cathode capillary is activated only after the first cathode capillary is deactivated, but alternatively, the second cathode capillary may be activated before or together with the deactivation of the first cathode capillary.

[0022] In the second variant of the method, as already described above in the first variant, the first actuator 17a is used to first adjust the amount of gas flowing through the first cathode capillary 11a, which is suitable for forming an arc discharge between the first cathode capillary 11a and the anode device 13. Thus, initially, only the first cathode capillary 11a is activated, thereby generating a plasma, which can be used to process one or more substrates in the vacuum chamber. If, at a later time, a stronger plasma is required to process substrates in the vacuum chamber, the second actuator 17b is used to adjust the amount of gas flowing through the second cathode capillary 11b, which is suitable for forming an arc discharge between the second cathode capillary 11b and the anode device 13, thereby generating an additional plasma cloud. In this case, the current intensity for maintaining each arc discharge can be adjusted separately for each cathode capillary. Due to the proximity of the two cathode capillaries 11 a and 11 b to each other, their plasma clouds at least partially pass through each other, allowing for the generation of a higher power overall plasma. If a lower power plasma is required at a later time, the arc discharge of one of the two cathode capillaries 11 a and 11 b activated at this time can be extinguished.

[0023] In the embodiment of the hollow cathode system according to the invention shown in FIG. 1, the cathode capillary arrangement includes a total of two cathode capillaries. However, hollow cathode systems according to the invention can also use cathode capillary arrangements that include more than two cathode capillaries. The invention does not impose an upper limit on the number of cathode capillaries. What is important for the invention is only that the cathode capillaries are electrically conductively connected to one another and that directly adjacent cathode capillaries are spaced apart by a maximum of 20 mm.

[0024] FIG. 2a shows a schematic cross-sectional view of an exemplary cathode capillary arrangement 20 according to the present invention, which comprises three cathode capillaries 21a-21c. The cathode capillaries 21a-21c are electrically conductively connected to one another using contact elements 28a-28c. As already described for the device 10 of FIG. 1, according to the present invention, each of the cathode capillaries 21a-21c is associated with a separate actuator, which can be used to separately control the gas flow through the associated cathode capillary. Thus, arc discharges can be generated separately from each of the cathode capillaries 21a-21c toward the anode device, thereby enabling the hollow cathode system according to the present invention to be operated by the cathode capillary arrangement 20 in the two method variants previously described for the embodiment according to FIG. 1. The same applies to the hollow cathode system according to the present invention with all of the cathode capillary arrangements described below. 2b, the cathode capillary arrangement 20 known from FIG. 2a is again shown in a schematic cross-sectional view. In the embodiment according to FIG. 2b, the cathode capillary arrangement 20 is surrounded by an annular element 23 of the anode device associated with the cathode capillary at least at the end of the cathode capillary where the outlet opening of the cathode capillary is located. With an annular anode arranged in this way, the cathode capillaries of the hollow cathode system according to the invention can also be operated using a method as described, for example, in DE 10 2006 027 853 A1. The annular element 23 of the anode device can also be used in all cathode capillary arrangements described above and below, where the annular element surrounds all cathode capillaries of the cathode capillary arrangement at least at the end of the cathode capillary where the gas outlet opening of the cathode capillary is located.

[0025] In all of the previously described embodiments, the cathode capillaries of the hollow cathode system according to the invention are formed as separate capillaries that are electrically conductively connected to one another by means of contact elements. A schematic cross-sectional view of a cathode capillary arrangement 30 is shown in FIG. 3 , in which a block 38 made of electrically conductive material has four cylindrical cutouts 31 a-31 d extending through the entire length of the block 38. The four cutouts 31 a-31 d with cylindrical peripheral surfaces in the block 38 function as cathode capillaries through which the working gas flows to form the arc discharge. Each cutout 31 a-31 d is associated with a separate actuator, which allows separate control of the gas flow through the associated cutout.

[0026] As already mentioned above, hollow cathode systems typically include auxiliary devices, such as heating coils with associated current supplies, by means of which arc discharges can be ignited in the cathode capillaries. In all previously described embodiments of the present invention, such auxiliary devices for igniting arc discharges can also be associated with the cathode capillaries. Thus, for example, in embodiments in which the cathode capillaries are formed as separate capillaries, such as in the embodiment according to FIGS. 1 to 2b, a separate heating coil can be wound around each cathode capillary or a separate heating element can be associated with each cathode capillary. In the embodiment according to FIG. 3, for example, a heating coil can be wound around block 38.

[0027] FIG. 4 shows a schematic cross-sectional view of a cathode capillary arrangement 40, including four cathode capillaries 41a-41d, electrically connected to one another using contact elements 48a-48d. Using the cathode capillaries 41a-41d, plasma can be generated in a vacuum chamber, corresponding to the approach described above, and this plasma can be used to process at least one substrate in the vacuum chamber. A separate cathode capillary 49 is positioned in the center of the four cathode capillaries 41a-41d. This cathode capillary 49 is electrically isolated from the four cathode capillaries 41a-41d and is associated with a separate power supply for generating an arc discharge. During operation of the hollow cathode system according to the present invention, including the cathode capillary arrangement 40, an arc discharge is first ignited by the cathode capillary 49, thereby generating plasma. However, the plasma generated using the cathode capillaries 49 is formed at a lower intensity than the plasma that can be formed using the cathode capillaries 41 a-41 d. The plasma generated using the cathode capillaries 49 is not ostensibly involved in processing the substrate, but is primarily used to supply charge carriers in the space between the cathode capillaries and the anode device that facilitates ignition of at least one of the cathode capillaries 41 a-41 d.

[0028] The plasma generated using the cathode capillary tube 49 has a lower intensity and therefore experiences less wear than the cathode capillaries 41a-41d. Therefore, by using the cathode capillary tube 49, an arc discharge can be maintained while the cathode capillaries 41a-41d are activated sequentially or alternately throughout the entire operating time of the hollow cathode system according to the present invention having the cathode capillary tube arrangement 40.

[0029] As already mentioned, the hollow cathode system according to the present invention involves at least two cathode capillaries, where, for example, at least one first cathode capillary may be activated while at least one second cathode capillary is inactive during operation of the hollow cathode system. During the period when the second cathode capillary is inactive, either no gas can flow through the second cathode capillary, or only a small amount of gas that is not suitable for forming an arc discharge between the second cathode capillary and the associated anode device can flow through the second cathode capillary. In this case, the flow of gas through the second cathode capillary with an amount of gas less than that required for forming an arc discharge is used to purge the second cathode capillary, thereby preventing the second cathode capillary from being clogged with particles, for example, particles that may be displaced by the activated first cathode capillary or particles that may originate from the coating material used to coat a substrate in a vacuum chamber. The purge gas for the inactive cathode capillaries can be, for example, a working gas provided in a first gas reservoir, which also flows through the cathode capillaries to form an arc discharge. Alternatively, a different gas, preferably an inert gas, provided in a second gas reservoir can be used to purge the cathode capillaries.

[0030] If a different gas is used to purge the cathode capillaries than the gas used to ignite and maintain the arc, the type of gas flowing through each cathode capillary can be adjusted using, for example, an actuator that also adjusts the gas flow rate through each cathode capillary. Alternatively, the type of gas flowing through each cathode capillary can be adjusted using a separate actuator.

[0031] While the cathode capillaries are formed as separate capillaries in the embodiment according to Figures 1, 2a, 2b, and 4, and as cylindrical cutouts in the embodiment according to Figure 3, in Figure 5, cathode capillary arrangement 50 is shown in a schematic longitudinal cross section, forming a hybrid configuration consisting of separate cathode capillaries and cutouts in the material block. Cathode capillary arrangement 50 includes a base element 58 made of a conductive material, in which two cylindrical cutouts 59a and 59b are formed, extending through the entire length of base element 58. However, cutouts 59a and 59b do not extend over the entire length required for the cathode capillaries. Furthermore, the cathode capillary subelements 51a and 51b are also attached to the base element 58, preferably by means of a detachable connection, so that the tube axis 52a of the cathode capillary subelement 51a is the same as the cylindrical axis of the cylindrical cutout 59a, and the tube axis 52b of the cathode capillary subelement 51b is the same as the cylindrical axis of the cylindrical cutout 59b. Alternatively, the cylindrical axes of the cutouts and the tube axes of the associated cathode capillary subelements may be offset, for example, in order to deflect any type of radiation from the inside of the vacuum chamber. As a detachable connection, the cathode capillary subelements 51a and 51b may have an external thread that is screwed into the base element 58, for example. Thus, cutout 59a and associated cathode capillary sub-element 51a form a first cathode capillary in the combination, and cutout 59b and associated cathode capillary sub-element 51b form a second cathode capillary. Although cathode capillary arrangement 50 illustratively includes only two cathode capillaries, alternative embodiments may include more than just two cathode capillaries.

[0032] As already explained above, wear occurs primarily in a locally limited active area in hollow cathodes, which in the hollow cathode system having cathode capillary configuration 50 is limited to cathode capillary sub-elements 51a and 51b. Therefore, in cathode capillary configuration 50, only worn cathode capillary sub-elements need to be replaced, rather than the entire cathode capillary, thereby saving material. Significant material savings are achieved here if the lengths of cutouts 59a and 59b are each at least 30% of the dimension resulting from the sum of the lengths of the cutouts and the associated cathode capillary sub-elements.

Claims

1. A hollow cathode system for generating plasma, comprising at least one cathode capillary (11a; 11b), an anode device (13), a power supply (14) connected between the cathode capillary (11a; 11b) and the anode device (13) for supplying a voltage, and at least one gas reservoir (15) for supplying a gas to flow through the cathode capillary (11a; 11b), the hollow cathode system has at least two cathode capillaries (11a; 11b) electrically conductively connected to each other, each cathode capillary (11a; 11b) being associated with a separate actuator (17a; 17b), and the actuator (17a; 17b) can be used to adjust the amount of gas flowing through the cathode capillary (11a; 11b) associated with the actuator (17a; 17b); At least in the first cathode capillary (11a), a first actuator (17a) is used to adjust a first gas amount flowing through the first cathode capillary (11a), the first gas amount being suitable for igniting an arc discharge between the first cathode capillary (11a) and the anode device (13); at least in the second cathode capillary (11b), a second actuator (17b) is used to adjust the amount of second gas flowing through the second cathode capillary (11b), the amount of second gas being unsuitable for igniting an arc discharge between the second cathode capillary (11b) and the anode device (13). Hollow cathode system.

2. A hollow cathode system for generating plasma, comprising at least one cathode capillary (11a; 11b), an anode device (13), a power supply (14) for supplying a voltage connected between the cathode capillary (11a; 11b) and the anode device (13), and at least one gas reservoir (15) for supplying a gas to flow through the cathode capillary (11a; 11b), the hollow cathode system has at least two cathode capillaries (11a; 11b) electrically conductively connected to each other, each cathode capillary (11a; 11b) being associated with a separate actuator (17a; 17b), and the actuator (17a; 17b) can be used to adjust the amount of gas flowing through the cathode capillary (11a; 11b) associated with the actuator (17a; 17b); At least in the first cathode capillary tube (11a) where an arc discharge is formed between the first cathode capillary tube (11a) and the anode device (13), the arc discharge is terminated; At least in the second cathode capillary tube (11b) where no arc discharge is formed between the second cathode capillary tube (11b) and the anode device (13), the arc discharge is ignited. Hollow cathode system.

3. the tube axes (12a; 12b) of at least two of the cathode capillaries (11a; 11b) are oriented parallel to one another or have an angle of at most 5° with respect to one another, 3. The hollow cathode system according to claim 1 or 2.

4. the gas flow direction through at least two of the cathode capillaries (11a; 11b) is the same, 4. A hollow cathode system according to any one of claims 1 to 3.

5. adjacent cathode capillaries (11a; 11b) have a maximum spacing of 20 mm from each other, 5. A hollow cathode system according to any one of claims 1 to 4.

6. at least one element (23) of the anode device is annularly formed and surrounds at least two of the cathode capillaries (21a; 21b; 21c), 6. A hollow cathode system according to any one of claims 1 to 5.

7. A method for operating a hollow cathode system using an anode device (13), a power supply (14) connected between the cathode capillaries (11a; 11b) and the anode device (13) for supplying a voltage, and at least one gas reservoir (15) for supplying gas to flow through the cathode capillaries (11a; 11b), comprising: using at least two cathode capillaries (11a; 11b) electrically conductively connected to each other, each cathode capillary (11a; 11b) being associated with a separate actuator (17a; 17b), and using the actuator (17a; 17b) to adjust the amount and / or type of gas flowing through the cathode capillary (11a; 11b) associated with the respective actuator (17a; 17b); At least in the first cathode capillary (11a), a first actuator (17a) is used to adjust a first gas amount flowing through the first cathode capillary (11a), the first gas amount being suitable for igniting an arc discharge between the first cathode capillary (11a) and the anode device (13); at least in the second cathode capillary (11b), a second actuator (17b) is used to adjust the amount of second gas flowing through the second cathode capillary (11b), the amount of second gas being unsuitable for igniting an arc discharge between the second cathode capillary (11b) and the anode device (13). method.

8. A method for operating a hollow cathode system using an anode device (13), a power supply (14) for supplying a voltage connected between a cathode capillary (11a; 11b) and the anode device (13), and at least one gas reservoir (15) for supplying gas flowing through the cathode capillary (11a; 11b), comprising: using at least two cathode capillaries (11a; 11b) electrically conductively connected to each other, each cathode capillary (11a; 11b) being associated with a separate actuator (17a; 17b), and using the actuator (17a; 17b) to adjust the amount and / or type of gas flowing through the cathode capillary (11a; 11b) associated with the respective actuator (17a; 17b); At least in the first cathode capillary tube (11a) where an arc discharge is formed between the first cathode capillary tube (11a) and the anode device (13), the arc discharge is terminated; At least in the second cathode capillary tube (11b) where no arc discharge is formed between the second cathode capillary tube (11b) and the anode device (13), the arc discharge is ignited. method.

9. 1. The method of claim 1, wherein at least two cathode capillaries (11a; 11b) simultaneously maintain an arc discharge towards the anode device (13) with a current intensity that can be adjusted separately for each cathode capillary.

9. The method according to claim 7 or 8.

10. The type of gas flowing through the cathode capillary tube (11a; 11b) associated with each of the actuators (17a; 17b) is also adjusted using the separate actuators (17a; 17b).

10. The method according to any one of claims 7 to 9.

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