Abstract:
A method for introducing a protective gas into an annular space of a receiver tube, in particular for solar collectors, is provided where the annular space is formed at least by one outer cladding tube and an inner absorber tube of the receiver tube and the outer cladding tube is connected to the absorber tube by a wall. The method includes producing an opening that penetrates the cladding tube or the wall, introducing protective gas through the opening into the annular space, and subsequently closing the opening.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/EP2015/069350 filed Aug. 24, 2015, which claims the benefit of German Application No. 10 2014 218 333.2 filed Sep. 12, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method for introducing a protective gas into an annular space of a receiver tube, wherein the annular space is formed between an outer cladding tube and an inner absorber tube of the receiver tube and the outer cladding tube is connected to the absorber tube in a gastight manner by means of a wall. The wall is generally composed of metal and contains a glass-metal transition element, an expansion compensation element, as well as additional connecting elements. Furthermore, the invention relates to a device for introducing protective gas into the annular space of the receiver tube. 
         [0004]    2. Description of Related Art 
         [0005]    Solar collectors have a collector mirror—for example, a parabolic cylindrical mirror (parabolic trough)—and a receiver tube, and are utilized in solar thermal power plants preferably for the generation of electricity. The receiver tube is arranged in the focal line of each collector mirror and is generally composed of an absorber tube, which has a radiation-absorbing layer, and a cladding tube made of glass, which surrounds the absorber tube and thermally insulates it. In the known solar thermal power plants, a thermal oil, which is utilized as a heat-transfer medium, is carried through the absorber tube and can be heated to a temperature of about 400° C. by means of the solar radiation reflected from the collector mirrors and focused on the absorber tube. This heated oil is finally introduced into a vaporization process, by means of which the thermal energy stored in the thermal oil can be converted to electrical energy. 
         [0006]    An annular space is formed in the receiver tube between the absorber tube and the cladding tube. This annular space serves to minimize heat losses at the outer surface of the absorber tube and thereby to increase the efficiency of the solar collector. For this purpose, the annular space is evacuated in order to obtain a thermal conductivity that is as low as possible. 
         [0007]    However, on account of the high thermal load, the thermal oil utilized as heat-transfer medium in the absorber tube does not exhibit long-term stability and releases hydrogen with increasing aging. The quantity released during the aging process depends, on the one hand, on the thermal oil used and the operating conditions in the solar thermal power plants and, on the other hand, on the water content, which, in particular, can form with the oil during the vaporization process. 
         [0008]    By permeation, the released hydrogen enters the evacuated annular space. In consequence, the pressure and the thermal conductivity of the annular space increase as well. This occurs until an equilibrium prevails between the partial pressures of hydrogen in the absorber tube and in the annular space. A particular drawback in this case is that hydrogen has a higher thermal conductivity than air, for example, so that, as the permeation of hydrogen progresses further, the thermal conductivity in the annular space is even better than that of the air outside of the receiver tube. In consequence, the efficiency of the receiver tube decreases and hence so does that of the complete solar collector. 
         [0009]    In order to counteract this increase in the partial pressure of hydrogen in the annular space and thereby prolong the service life of the receiver tube, various solutions are known from the prior art. 
         [0010]    For example, the hydrogen that has diffused into the annular space can be bound by means of getter materials. However, the absorption capacity of such materials is limited, so that, once the maximum absorption capacity of the getter materials has been attained, no further hydrogen can be bound and the pressure in the annular space increases once again. 
         [0011]    Receiver tubes with a getter material arranged in the annular space are known from WO 2004/063640 A1, for example. In the device described in said specification, the getter material is arranged in getter bridges between the absorber tube and the cladding tube directly in the annular space. The getter bridges produce a spacing between the absorber tube and the getter, so that the thermal load on the getter is reduced and its long-term stability is thereby improved. However, apart from the use of a getter material, no other solution for diminishing the hydrogen concentration in the annular space has been provided, so that the drawbacks of the getter described above still remain. 
         [0012]    In order to alleviate the problem of getter materials, DE 198 21 137 A1 discloses a receiver tube for solar thermal applications, in which, in addition, a noble gas with a partial pressure of up to several hundred mbar is present in the annular space. The advantage of this solution is that many noble gases have a lower thermal conductivity than hydrogen, so that the thermal conductance through the annular space and the deterioration in efficiency associated therewith can be reduced. However, the drawback of this design is that the annular space is filled with noble gas from the very start, so that, already directly after installation of the solar collector, an optimal efficiency of the receiver tube, as in the case of an evacuated annular space, is not achieved. 
         [0013]    Alternative embodiments, such as, for example, those disclosed in DE 10 2005 057 276 B3, provide for at least one gastight sealed tank, filled with at least one noble gas, in the annular space, from which the noble gas is introduced into the annular space once the getter material is exhausted. The drawback of this alternative embodiment is that the solar collector and, in particular, the receiver tube must be already fabricated with a filled tank. Retrofitting is not possible, so that the customer needs to make a decision directly during fabrication of the receiver tube about whether to bear the extra costs and the increased work effort involved. Another problem is posed by the opening of the tank, which can be carried out only with increased effort. 
         [0014]    A method for opening the tank and for filling the annular space with noble gas is known from DE 10 2011 082 772 B9, wherein the tank is opened by means of a laser drilling method. A laser beam is deflected from outside through the cladding tube onto the tank, which is irradiated until an opening forms in the tank and the protective gas is released. However, a drawback of this invention is also that retrofitting of the receiver tube with the protective gas tank is not possible and the customer needs to bear the increased costs and fabrication effort already during fabrication, even though the noble gas is only utilized a long time after startup. 
         [0015]    A method for opening of holes in work pieces of a general kind by using focused laser pulses is described in the Unexamined Patent Specification DE 27 11 889 A1, for example. 
         [0016]    Therefore, it is the object of the invention to provide a method and a device that make possible the filling of the annular space of a receiver tube with a protective gas and, in addition, the subsequent filling thereof. 
       SUMMARY 
       [0017]    The method according to the invention for introducing a protective gas into an annular space of a receiver tube, in particular for solar collectors, wherein the annular space is formed between one outer cladding tube and an inner absorber tube of the receiver tube and the outer cladding tube is connected to the absorber tube by means of a wall, is characterized in that, in a first process step, an opening that penetrates the cladding tube or the wall is produced. Subsequently, protective gas is introduced through the opening into the annular space and, in a third process step, the opening is subsequently closed again. 
         [0018]    The advantage of this method according to the invention is that the annular space of a receiver tube that has already been manufactured and even already installed in a solar collector can be filled subsequently with a protective gas and without great effort in terms of time or cost. Furthermore, the receiver tube can be supplied with an initially evacuated annular space, so that, at the very start of use, it is possible to realize a maximum efficiency. However, once the efficiency of the receiver tube reaches a critical value on account of hydrogen diffusion, the annular space can be filled with a protective gas in accordance with the method according to the invention, and thus it is possible to stop any further drop in efficiency. 
         [0019]    The cost- and fabrication-intensive installation of an additional tank filled with protective gas is dispensed with. In addition, the annular spaces of already existing equipment can also be filled with noble gas at any time by means of the method according to the invention and hence a further reduction in efficiency can be stopped. In this way, the service life of all receiver tubes is increased, which offers a substantial economic and ecological advantage. 
         [0020]    In the process, the critical value can be derived from the hydrogen concentration actually present in the annular space, which is measured by suitable sensors. A temperature measured at the glass cladding tube is also a suitable indicator, because, with increasing hydrogen concentration, the thermal conductivity of the annular space and thus also the temperature of the glass cladding tube increase during operation. Furthermore, the time or the efficiency of the solar collectors can also constitute the critical value. 
         [0021]    In an advantageous embodiment of the method according to the invention, the opening is formed by means of a laser drilling method. 
         [0022]    The laser drilling method has the advantage that, in principle, openings of any size and shape can be produced. To this end, it is merely necessary to adapt the power and/or geometry of the laser beam to the respective geometries and natures of the receiver tubes, cladding tubes, and/or walls. Furthermore, the laser drilling method equally offers the possibility of producing the opening either in the cladding tube, which is primarily composed of glass, or in the wall, which is primarily composed of metal or a metal alloy, by using the same device. In contrast to material-removing drilling processes, a laser drilling method makes it possible to produce openings without any abrasion, as a result of which contamination of the annular space is prevented. 
         [0023]    In another advantageous embodiment, the opening is closed again by means of a laser welding method. 
         [0024]    The closure by means of a laser welding method offers the advantage that the opening can be closed without additional application of a closing material. Furthermore, a laser beam can be adapted by variation of its power and/or geometry to the most diverse opening geometries and to different requirements, such as, for example, the wall thickness of the cladding tube or the wall or the material compositions thereof. 
         [0025]    Another advantageous embodiment provides that the opening is produced under a pressure gradient from outside to inside into the annular space. 
         [0026]    This embodiment provides that, outside of the cladding tube and consequently from the side facing away from the absorber tube, a higher pressure prevails than in the annular space. This elevated pressure can occur, for example, by imposing pressure by means of protective gas. This embodiment offers the advantage that protective gas already penetrates into the annular space once an opening is present and the filling process of the annular space is thereby shortened in time. In addition, any contamination of the annular space with foreign gases is also strongly restricted. The pressure gradient further leads to the possibility that very small openings, which can also be produced by means of a laser drilling method, remain open and fused material does not run once again into the opening and, as a result, a subsequent continuous filling process is made possible in spite of very small openings. 
         [0027]    In a likewise advantageous embodiment, the opening is produced by means of a laser drilling method with a laser beam diameter d L   1  and the opening can be closed, after the process chamber has been filled, by means of a laser welding method with a laser beam diameter d L   2 , where d L   2  is greater than d L   1 . This embodiment offers the possibility of producing and again closing the opening by use of only one laser apparatus. When the opening is closed, it is merely necessary to widen the diameter of the laser beam by means of an optical system, for example. Afterwards, the opening is irradiated with a laser beam, the radius of which is greater than the opening radius. The result of this is that the material lying around the opening is heated by absorption and finally fused. These fused areas subsequently flow into the opening and close it. 
         [0028]    In an alternative and further embodiment according to the invention, the closure of the opening occurs using an additional closing material. 
         [0029]    Especially in the case of thin-walled cladding tubes or walls, it is possible that insufficient material is available for closure of the opening by fusion, so that the stability of the cladding tube or the wall is not ensured in the region of the closed opening. In such cases, in accordance with the invention, additional material is introduced onto or into the opening, as a result of which the opening is closed and also the surrounding material of the cladding tube or the wall is not impaired or is less impaired. 
         [0030]    Another embodiment according to the invention provides that, prior to creation of the opening, the additional closure material is applied to the site of the tubular jacket or the wall that is to be opened. 
         [0031]    The opening is produced all the way through the applied closure material. The closure material thereby has no significant influence on the opening step and filling process of the annular space. This embodiment also has the advantage that it is not necessary to use any direct material of the cladding tube or the wall for closure of the opening. Sufficient additional material is available, so that any impairment of the stability of the cladding tube or/and the wall is prevented. 
         [0032]    Also advantageous is an embodiment in which the closure material is applied by a soldering, welding, or adhesive method. 
         [0033]    By means of all these methods, the closure material is arranged in fixed position on the cladding tube or the wall, so that the danger of it shifting out of place during the opening step or filling process is diminished. 
         [0034]    The additional closure material is fused after the annular space has been filled and subsequently runs at least partially into the opening so as to close it. 
         [0035]    The fusion of the closure material can occur, as described above, by means of a laser beam, the diameter of which is greater than the opening diameter. In addition, it is possible to choose as a closure material a material with a melting temperature below that of the cladding tube or the wall, as a result of which, during fusion, markedly less energy is required and the local thermal load on the cladding tube or the wall is reduced further. Alternatively, the fusion can also occur by way of directly introduced thermal energy. 
         [0036]    Alternatively to the applied closure material, it is provided in another advantageous embodiment that the closure material is pushed into or onto the opening only after filling of the annular space and hence the opening is closed at least partially. 
         [0037]    Introducing the closure material only after filling of the annular space makes possible a smooth and undisturbed opening and filling process. Nonetheless, through the use of a closure material, there is sufficient additional material for the closure of the opening. The introduction of material into or onto the opening can be automated and/or it can occur under computer control, so that the opening can be closed in a specific and reliable manner. 
         [0038]    In another embodiment according to the invention, the closure material is pushed into or onto the opening after filling of the annular space and fused at least partially by means of a laser, as a result of which the opening is closed. 
         [0039]    This has the advantage that, owing to fusion of the separate closure material, the thermal load and potential damage to the cladding tube and/or wall entailed therewith can be prevented. 
         [0040]    Another advantageous embodiment of the method according to the invention is characterized in that the opening is produced with at least two different diameters d O   1  and d O   2 , where d O   2  represents the opening diameter at the side facing away from the absorber tube and d O   1  represents the opening diameter at the side of the cladding tube or wall facing the absorber tube, where the following holds: d O   2 &gt;d O   1 . 
         [0041]    Owing to the enlarged diameter at the outer side of the cladding tube, the introduction of an additional closure material into the opening is facilitated. In addition, this design of the opening in the form of a stepped drill hole makes possible a secure closure process. As a result of the fusion of a closure material in or at the opening diameter d O   2 , the closure material runs both into the opening region with smaller diameter and also into the opening region with larger diameter. This leads to a minimization of potential cavities in the closure material inside of the opening and hence also to the minimization of potential admissions of gas. 
         [0042]    In another advantageous embodiment, the opening in the wall is closed by means of resistance welding. 
         [0043]    Owing to the fact that the wall is particularly composed of metal or a metal alloy, it conducts the current. Accordingly, through application of a voltage, closure of the opening is possible by means of resistance welding. The great advantage of this welding technique consists in the possibility of concentrating a high energy in the form of electric current onto a small area of a work piece within a very short time, whereby, under supply of high pressure (pneumatic or electromechanical), an irreversible connection is produced. As a result, the opening that is produced can be closed in a fast and firm manner. 
         [0044]    This advantageous embodiment can also occur by using an additional closure material. 
         [0045]    Another embodiment is characterized in that the closure of the opening occurs by using at least one rod electrode. 
         [0046]    Through the use of at least one rod electrode, it is possible to restrict the effect of resistance welding to the opening in a highly specific and local manner. Accordingly, surrounding areas of the wall are not influenced. Furthermore, it is possible through the choice of suitable geometries of the rod electrodes to enable the resistance welding of different embodiments of the wall as well. In addition, the rod electrode enables an adequate pressure to be applied locally in the region of the opening, as a result of which closure is simplified and also promoted. 
         [0047]    Another and likewise advantageous embodiment provides that, after filling of the annular space, the closure material is pushed at least partially into or onto the opening, at least one electrode is contacted in each instance with the closure material and with the wall, the closure material is fused by means of resistance welding, and hence the opening is closed. 
         [0048]    In this embodiment, all of the aforementioned advantages of resistance welding and the use of a closure material are combined. 
         [0049]    In another embodiment, the opening is produced mechanically. Mechanical opening can occur by using a mandrel, for example. In the process the mandrel is pressed through the wall and then pulled back out, as a result of which a corresponding opening is produced through the wall. 
         [0050]    In an advantageous embodiment, however, the opening is produced through the use of a cannula, with the cannula being pressed through the wall. 
         [0051]    The use of a cannula has the advantage that a direct access to the annular space through the cavity of the cannula is formed, so that the cannula does not need to be pulled back out once again from the opening. After puncturing with the cannula has occurred, a segment of the cannula is located in the annular space, while another segment protrudes from the wall and enables intakes for the introduction of a protective gas to be easily attached. In this case, the cannula acts like a cannula of a syringe and simplifies the subsequent filling process. Furthermore, the use of a cannula also benefits the later closure of the opening. 
         [0052]    Thus, another embodiment according to the invention provides that the cannula is pressed through the wall, the annular space is filled via the cannula, and the opening is subsequently closed by closure of the cannula. 
         [0053]    The advantage of this embodiment lies in the fact that the wall is pierced only one time by means of the cannula and all further method steps occur via this cannula. When the annular space is opened and closed, the thermal load on the wall is thus reduced. Furthermore, the closure of the opening occurs indirectly by closing the cannula. In the process, the cannula is substantially more readily accessible and easier to close, so that, here, too, there is a simplification and thus entailed time savings during the closure. 
         [0054]    Advantageously, the cannula is closed by at least one of the following methods: resistance welding, friction welding, or induction soldering. 
         [0055]    This method, by means of which a closure of the cannula can occur rapidly and reliably, has been long tried and tested. In order to make possible resistance welding, the cannula is composed at least partially of metal or an alloy. 
         [0056]    Another advantageous embodiment of the method according to the invention is characterized in that, prior to the creation of the opening, an evacuated process chamber is arranged at the cladding tube and/or the wall at the place to be opened in an enclosing and gastight manner, then evacuated and filled with protective gas. 
         [0057]    Accordingly, the introduction of a protective gas into an annular space of a receiver tube takes place from this process chamber. The advantage of this process chamber consists in the fact that the method can be carried out in a manner that is protected against all environmental influences, such as, for example, pressure or humidity, but also against mechanical loads or foreign particles. Any contamination of the process chamber is thereby prevented. It is possible in the process chamber to adjust any environmental parameters, as a result of which the method can be carried out flexibly and independent of climatic influences. Furthermore, the process chamber makes it possible for all method means required for the method to be arranged already beforehand inside of the process chamber, so that the process chamber need not be opened during the method. 
         [0058]    In a likewise advantageous embodiment, after creation of the opening, it is waited until the desired gas exchange has occurred between the annular space and the process chamber. 
         [0059]    On account of this limited opening diameter, it is necessary, once the protective gas has been introduced into the process chamber, to wait for a certain time until the protective gas has become distributed inside of the annular space with the intended partial pressure. This waiting time depends on the opening diameter, the protective gas, and the difference in pressure between the annular space and the protective gas reservoir. The filling process can be monitored directly by means of pressure measurements or by means of time measurements, when the pressure relations and the opening diameter are known. 
         [0060]    Subsequent to the gas exchange, the opening is closed and the process chamber is then ventilated and once again separated from the receiver tube. 
         [0061]    Accordingly, the process chamber can be attached reversibly to the receiver tube and reused several times and for various receiver tubes. 
         [0062]    Alternatively, however, the process chamber can also be connected irreversibly to the wall and/or to the cladding tube, so that, subsequent to the gas exchange, the opening is closed and, even though the process chamber is ventilated, it is not separated once again from the receiver tube. 
         [0063]    Besides relating to a method, the invention also relates to a device for introducing a protective gas into the annular space of a receiver tube, said device being referred to hereinafter as a “filling device,” in particular for solar collectors, in which the annular space is formed between an outer cladding tube and an inner absorber tube of the receiver tube and the outer cladding tube is connected to the absorber tube in a gastight manner by means of a wall and the device includes a process chamber, means for producing an opening through the cladding tube or the wall, means for introducing protective gas into the annular space, and means for closing the opening. 
         [0064]    This device offers the advantages discussed above in connection with the method according to the invention. 
         [0065]    In an advantageous embodiment, the means for producing an opening through the cladding tube or the wall are constituted by a laser system. This laser system offers the possibility of producing openings through the tubular jacket or the wall with diverse diameters and geometries rapidly and without material removal. Detailed advantages of a laser system have already been explained in connection with the description of the method according to the invention. 
         [0066]    In a likewise advantageous embodiment, the means for producing an opening through the wall are constituted by a punching system with a cannula arranged at this punching system. 
         [0067]    Furthermore, the means for introducing protective gas into the annular space are constituted advantageously by a gas supply system. This supply system makes possible a rapid and cost-effective filling process of the annular space. In this case, the gas supply system has a gas tank, which is arranged in an exchangeable manner in the gas supply system. Thus, a rapid exchange of the process gas or replacement of an empty gas tank is made possible. 
         [0068]    Another advantageous embodiment of the device is characterized in that the means for closing the opening are constituted by a laser system or a laser system with closure material or a heating system, such as, for example, an induction coil or a heating coil with closure material. 
         [0069]    Reference is made, in turn, to the descriptions of advantages in connection with the method according to the invention for the respective advantages of the individual components of the device. 
         [0070]    Likewise advantageous is an embodiment in which the process chamber has an outlet opening for evacuating the process chamber, a lead-through opening for the means for producing the opening through the cladding tube or the wall, and an inlet opening for filling the process chamber with protective gas. It is possible by way of these openings to achieve a fast and cost-effective operation of the device and an efficient implementation of the method. 
         [0071]    In another advantageous embodiment, the process chamber can be connected via the outlet opening to a vacuum system, via the inlet opening to a gas supply system, and via the lead-through opening to a laser system or a punching system. 
         [0072]    In order to ensure a rapid fastening of the process chamber at the receiver tube and, in particular, at the wall, means for reversible fastening of the process chamber at the receiver tube and, in particular, at the wall are arranged at the process chamber. 
         [0073]    In another embodiment, in addition to the process chamber, a support system, which is connected to the process chamber through a vacuum-tight corrugated hose connection, is provided. This arrangement has the advantage that all mechanically acting forces of the laser, the pump, etc., which are connected to the support system, are absorbed by the support system and hence the sealing at the wall is not subjected to a mechanical load. In addition, the corrugated hose connection can be attached for receiving the laser, so as to achieve a complete encapsulation of the laser beam path. 
         [0074]    The process chamber is equipped with a vacuum-tight window that is transparent for the laser beam. In addition, a protective glass can be attached in the process chamber, said protective glass being preferably rotatable and protecting the laser window against vapor deposition during the opening process. The support system has a further camera system with connecting ports for the pumping and gas supply system, including all required sensors as well as a mount and calibrating apparatus for the laser head. Instead of a gas line, it is also possible to use preferably a prefilled gas cartridge, which is exchanged prior to each new filling process. Preferably, there is also a connecting port at the camera system for receiving a vacuum getter, which ensures the maintenance of the gas purity during the filling process. Alternatively, the getter can also be introduced into the noble gas cartridge prior to the filling process and then activated after closure. 
         [0075]    In another preferred embodiment, it is possible to use a vaporized barium getter in a glass tube, said vaporized barium getter being used at the same time as an indicator for the quality of the filling operation. It is possible by use of a getter to dismantle the pumping system under noble gas atmosphere prior to opening of the receiver and the opening process can be carried out after flooding of the chamber with noble gas. In this way, interfering vibrations due to the pumping system can be prevented and the process safety can be improved. Moreover, it is thereby possible prior to opening to ensure that the camera system is still gastight after the flooding. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0076]    Further features, advantages, and exemplary embodiments of the method and the device for introducing a protective gas into an annular space are discussed below on the basis of the description of figures. Shown are: 
           [0077]      FIG. 1 a    a first embodiment of the filling device, 
           [0078]      FIGS. 1 b -1 c    the filling device during various process steps for filling an annular space, 
           [0079]      FIG. 2 a    a second embodiment of the filling device, 
           [0080]      FIGS. 2 b -2 d    the filling device of the second embodiment during various process steps for filling an annular space, 
           [0081]      FIG. 3 a    a third embodiment of the filling device, 
           [0082]      FIGS. 3 b -3 e    the filling device of the third embodiment during various process steps for filling of an annular space, 
           [0083]      FIG. 4 a    a fourth embodiment of the filling device, 
           [0084]      FIGS. 4 b -4 e    the filling device of the fourth embodiment during various process steps for filling of an annular space, 
           [0085]      FIG. 5 a    fifth embodiment of the filling device, 
           [0086]      FIG. 5 b    an enlarged illustration of the process chamber according to the fifth embodiment, 
           [0087]      FIG. 6 a    a sixth embodiment of the filling device, and 
           [0088]      FIG. 6 b    an enlarged illustration of the process chamber according to the sixth embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0089]    A first embodiment of the filling device  100  according to the invention is illustrated in  FIG. 1   a.  This device  100  has a process chamber  101 , which can be fixed in place at a receiver tube  4  by way of a fastening system  20 , which is composed of a clamp  21  and a fastener  22 . The receiver tube  4  is characterized by an absorber tube  1  and a cladding tube  2 , with an annular space  3  being formed between the absorber tube  1  and the cladding tube  2 . The filling device  100  is fastened at the cladding tube  2  or preferably at the wall  5  by means of the clamp  21 . The wall  5  contains an expansion compensation piece, which is not illustrated in  FIG. 1  and was already discussed in the introductory section. Further elaborating details in regard to the wall  5  are discussed in connection with  FIG. 5   b.  Alternatively, the filling device  100  can also be placed directly on the glass of the cladding tube  2 . Preferably, the fastening system  20  is arranged partially at a side wall  106  of the process chamber  101 , thereby producing a homogeneous compressive pressure on the wall  5  or on the cladding tube  2 . 
         [0090]    In order to be able to attach the process chamber  101  rapidly and reversibly to various receiver tubes  4  with different diameters of the cladding tube  2  or the wall  5 , the circumferential size of the clamp  21  can be adjusted variably by means of the fastener  22 . By way of example, commercially available worm clamps are suitable as a fastening system  20 . Alternatively to a clamp  21 , however, it is also possible to use a rubber band or strap for fixing in place the process chamber  101  on the receiver tube  4 . 
         [0091]    In order to seal off the interior of the process chamber  101  from external environmental influences, seals  102  are attached at contact sites between the process chamber  101  and the receiver tube  4 . These seals  102  can be designed, for example, as a sealing ring  102 . It is possible by means of the fastening system  20  and the seal  102  to fasten the interior of the process chamber  101  on the receiver tube  4  in a reversible manner. 
         [0092]    In order to be able to evacuate the process chamber  101 , said process chamber has an outlet opening  103  and is connected to a vacuum system  30  by means of a flange connection  33 . This vacuum system  30  includes a vacuum pump  31  and vacuum hoses  32 , with at least one vacuum hose  32  connecting the vacuum pump  31  to the process chamber  101  via the flange connection  33 . Accordingly, the process chamber  101  can be evacuated via the outlet opening  23   a  and pressures of several mbar can be obtained within the process chamber  101 . 
         [0093]    Furthermore, the process chamber  101  disposes over a lead-through opening  104 . In a first embodiment of the filling device  100 , this opening  104  connects the process chamber  101  to the laser system  40 . In this case, the laser system  40  has a laser source  41  in the form of a laser diode or a solid-state laser, for example. This laser source  41  is connected to a laser head  43  via at least one light guide  42 , with the laser head  43 , together with a flange connection  46 , constituting the connecting site between the laser system  40  and the process chamber  101 . In order to be able to adapt the laser beam emitted from the laser source  41  to the respective characteristics of the cladding tube  2  or the wall  5 , such as, for example, the material composition or wall thickness thereof, the laser head  43  has an optical system  44  for adjusting the beam width of the laser beam and a focusing unit  45  for controlling the focal point of the laser beam in the radial direction of the receiver tube  4 . Via the laser head  43 , the laser beam enters the interior of the process chamber  101  through the lead-through opening  104  and, with its focal point, finally reaches the surface of the cladding tube  2  or the wall  5  of the receiver tube  4 . 
         [0094]    In order to be able to fill the process chamber  101  with a gas and, in particular, with an inert process gas—for example, a noble gas—said process chamber is connected via an inlet opening  105  to a gas supply system  50 . The gas supply system  50  has a gas tank  51 , which is filled with the process gas and is connected to the process chamber  101  by means of a flange connection  52 . In order to be able to control the proportion of process gas inside of the process chamber  101 , a valve, for example, which is not illustrated in  FIG. 1   a,  is arranged between the flange connection  52  and the gas tank  51 . Alternatively, the flow rate of the process gas into the process chamber  101  can be analyzed and controlled by means of a gas flow meter, which is also arranged between the flange connection  52  and the gas tank  51  and is not illustrated in  FIG. 1   a.    
         [0095]    The inlet opening  105 , the lead-through opening  104 , and the outlet opening  103  are each arranged on the side of the process chamber  101 , namely, the cover wall  107 , that faces away from the receiver tube  4 . 
         [0096]    The various process steps for filling the annular space  3  of the receiver tube  4  will be discussed on the basis of  FIGS. 1 a  to 1 c    by means of a first embodiment of the filling device  100 . 
         [0097]    As can be seen in  FIG. 1   a,  in a first step, the filling device  100 , composed of the process chamber  101 , the vacuum system  30 , the laser system  40 , and the gas supply system  50 , is arranged at a receiver tube  4  and, in particular, at the wall  5  or cladding tube  2  thereof by means of a fastening system  20 . In the process, the seal  102  forms preferably the sole contact between the process chamber  101  and the wall  5  or the cladding tube  2 . Subsequently, the fastening system  20  is tightened, so that the process chamber  101  is pressed against the glass-metal transition element  5 . If the fastening system  20  is formed by a clamp  21 , for example, the tightening occurs by adjustment of the fastener  22 . 
         [0098]    Once the process chamber  101  has been placed on the cladding tube  2  or the wall  5  in a gastight manner, the interior thereof is evacuated via the outlet opening  103  by means of the vacuum pump  31  of the vacuum system  30 . This occurs until pressures of approximately 10 −3  to 10 −2  mbar prevail in the process chamber. As a result of this evacuation, the interior of the process chamber  101  is freed of foreign material, which could otherwise lead to a contamination of the annular space  3  when the cladding tube  2  or the wall  5  is later opened. 
         [0099]    Optionally, after evacuation of the process chamber  101  and prior to opening of the cladding tube  2  or the wall  5 , the interior of the process chamber  101  can be filled already with a process gas from the gas tank  51  of the gas supply system  50  via the inlet opening  105 . Such an application of pressure acts advantageously on the subsequent opening of the wall  5  or the cladding tube  2  in that the pressure prevents material from running into the holes. In addition, a prior filling of the process chamber  101  reduces the subsequent filling time of the annular space  3 . 
         [0100]    Once the process chamber  101  has been evacuated and optionally already filled with a process gas, an opening O 1  is produced through the wall  5  or directly through the cladding tube  2  by means of the laser system  40 , this being illustrated in  FIG. 1   b.    
         [0101]    In the laser source  41 , a laser beam is produced by laser diodes, for example, and directed via the light guide  42  into the laser head  43 . In this laser head  43 , the beam width of the laser beam is adjusted by means of the optical system  44 . It is also possible via the focusing unit  45  to adjust and alter the focal point of the laser beam along the axis L 1 . 
         [0102]    Accordingly, the laser beam produced in the laser source  41  is directed via the laser head and the lead-through opening  104  along the axis L 1  into the process chamber  101  and onto the surface of the cladding tube  2  or the wall  5 . Owing to the high energy of the laser beam, vaporization processes occur at the contact point of the laser beam and the cladding tube  2  or the wall  5 , so that material is removed. This occurs until a complete opening O 1  has been produced through the cladding tube  2  or the wall  5 . As a result, the interior of the process chamber  101  and the interior of the annular space  3  are connected spatially to each other and the process gas can flow out of the gas tank  51  of the gas supply system  50  via the inlet opening  105  into the interior of the process chamber  101  and via the opening O 1  into the annular space  3 . 
         [0103]    This occurs until the desired quantity of process gas has flowed into the annular space  3 . As characteristic parameters, it is possible in this case to measure, for example, the pressure inside of the process chamber  101 , the quantity of process gas flowing through the inlet opening  105 , or else the process time. 
         [0104]    Subsequent to this filling process, the opening O 1  is again closed, which is depicted in  FIG. 1   c.  For this purpose, the laser beam is widened in the focus thereof by the optical system  44 . Thus, the laser beam in the focal point has a larger diameter than the opening O 1  and no longer has the energy density of the material of the cladding tube  2  or the wall  5  required for vaporization, but rather only fuses this material. For closure of the opening O 1 , the widened laser beam is radiated along the axis L 1  onto the opening O 1 . As a result of this, the edges of the opening O 1  soften and finally fuse. The fused material then flows into the opening O 1  and closes it and, consequently, the annular space  3  and the process chamber  101  are once again separated spatially from each other. Accordingly, no additional closure material for the closure of the opening O 1  is necessary. 
         [0105]    In a last step, the fastening system  20  is released, as a result of which the filling device  100  can be removed completely from the receiver tube  4 . 
         [0106]    Illustrated in  FIG. 2 a    is a second embodiment of the filling device  200 , wherein, in analogy to the device  100  from  FIG. 1   a,  the process chamber  201  is fastened reversibly to the receiver tube  4  by means of a fastening system  20 . In this embodiment, too, the clamping force of the fastening system  20  and, in particular, the clamp  21  can be regulated by means of the fastener  22 , so that the compressive force of the process chamber  201  can be adjusted variably. 
         [0107]    In order to be able to seal off the interior of the process chamber  201  against external environmental influences, at least one seal  202  in the form of a sealing ring, for example, is also attached at the contact regions between the process chamber  201  and the receiver tube  4 , with the seal  202  in this embodiment as well preferably representing the sole contact between the process chamber  201  and the receiver tube  4 . By means of the fastening system  20  and the seal  21 , the interior of the process chamber  201  is fastened reversibly on the receiver tube  4 . 
         [0108]    As in the case of the first embodiment, the process chamber  201  also has an outlet opening  203 , a lead-through opening  204 , and an inlet opening  205 . In this case, the outlet opening  203  connects the interior of the process chamber  201  via the flange connection  33  to the vacuum system, which is not illustrated in  FIG. 2   a,  so that the process chamber  201  can be evacuated through the outlet opening  203 . The inlet opening  205 , in turn, connects the interior of the process chamber  201  to the gas supply system  50  by means of the flange connection  52 . In this case, the gas supply system  50  also has a gas tank  51 , which is filled with a process gas. Furthermore, the lead-through opening  204  connects the process chamber  201  via the flange connection  46  to the laser head  43  of the laser system, which is not shown in full in  FIG. 2   a.    
         [0109]    Further properties and features of the vacuum system, the laser system, and the gas supply system  50  are analogous to the filling device  100  illustrated in  FIG. 1   a,  with the exception of the positioning of the outlet opening  203 , of the lead-through opening  204 , and of the inlet opening  205 . In contrast to the filling device  100  illustrated in  FIG. 1   a,  the openings  203 ,  204 ,  205  in the second embodiment  200  are not integrated in the cover wall  207 , but rather in the side wall  206  of the process chamber  201 . In this case, the outlet opening  203  and the inlet opening  205  are arranged opposite-lying to the lead-through opening  204 . However, the lead-through opening  204  does not extend perpendicularly through the side wall  206 , but rather it is arranged at an angle in such a way that the laser beam passing through the opening  204  impinges inside of the process chamber  201  on the surface of the cladding tube  2  or the wall  5  of the receiver tube  4 . As a result of this arrangement of the lead-through opening  204  and the laser system connected to the lead-through opening  204 , an opening O 2  can be produced through the cladding tube  2  or the wall  5  by means of the laser beam, this opening O 2  being illustrated in  FIG. 2   b.    
         [0110]    In order to be able to close again the opening O 2  after gas exchange, a closure material  209  in the form of a welding wire is additionally arranged inside of the process chamber  201 . This welding wire  209  extends through the gastight lead-through opening  208  through the cover wall  207  along an axis D into the process chamber  201 . If the process chamber  201  is arranged on the receiver tube  4 , then the closure material  209  extends inside of the process chamber  201  preferably radially with respect to the receiver tube  4  from the cover wall  207  in the direction of the cladding tube  2  or the wall  5 . In this case, the closure material  209  is arranged along the axis D, which is preferably directed perpendicularly through the cover wall  207 , so as to be able to move in the direction of the axis D. Furthermore, the closure material  209 , the lead-through opening  204 , and the laser head  43  are arranged in such a way that the beam axis L 2  of the laser beam and the axis D of the closure material  209  meet at a point of intersection S on the surface of the cladding tube  2  or the wall  5  for the process chamber  201  mounted on the receiver  4 . This point of intersection S is located inside of the process chamber  201 . 
         [0111]    In order to be able to seal the process chamber  201  reliably against external environmental influences, the lead-through opening  208  is preferably designed as a vacuum lead-through opening. 
         [0112]    Alternatively to the fastening of the embodiments of the filling device  100 ,  200 , discussed in  FIGS. 1 a    and  2   a,  by means of the clamp  21 , the process chambers  101 ,  201  can also be directly connected reversibly to the receiver tube  4  and this will be discussed in detail in connection with  FIGS. 3 a    and  3   b.    
         [0113]    In  FIGS. 2 a    to  2   d,  the various process steps for filling the annular space  3  of the receiver tube  4  by means of the second embodiment of the filling device  200  are discussed. 
         [0114]    First of all, the process chamber  201  is arranged at the receiver tube  4  and, in particular, at the cladding tube  2  thereof or the wall  5  thereof by means of the fastening system  20 , with the seals  202  preferably forming the sole contact between the process chamber  201  and the cladding tube  2  or the wall  5 . 
         [0115]    Once the process chamber  201  has been placed on the cladding tube  2  or the wall  5  in a gastight manner, the interior thereof is evacuated via the outlet opening  203  by means of the vacuum system. Optionally, after evacuation of the process chamber  201  and prior to opening of the cladding tube  2  or the wall  5 , the interior of the process chamber  201  can be filled with a process gas via the inlet opening  205 . 
         [0116]    For detailed information on these process steps, reference is made at this point to the description of  FIG. 1   b,  because these steps are identical in the first and second embodiment of the filling device  100 ,  200 . 
         [0117]    Once the process chamber  201  has been evacuated and optionally filled with a process gas, an opening O 2  is produced through the cladding tube  2  or the wall  5  by means of the laser system, this being illustrated in  FIG. 2   b.  The creation of the opening O 2  occurs in analogy to that of the opening O 1  of the first embodiment form  100 . However, the opening O 2  does not extend radially through the cladding tube  2  or the wall  5 , but rather at an angle, with the central axis of the opening O 2  and the axis D intersecting in the interior of the process chamber  201  at the point S. Once the opening O 2  has been produced, the annular space  3  is once again spatially connected to the process chamber  201 , so that a filling of the annular space  3  with process gas can occur. This filling also occurs identically to the filling of the annular space  3  by use of the first embodiment of the filling device  100 . 
         [0118]    In order to be able to close again the opening O 2 , the closure material  209  is caused to travel along the axis D in the direction of the receiver tube  4  by using a stroke apparatus that is not illustrated in  FIG. 2   c.  This occurs until the closure material  209  at least contacts the axis L 2  of the laser beam. Preferably, however, the closure material extends to the cladding tube  2  or the wall  5 . Once the closure material  209  has reached this position, the laser beam melts the material  209  at the intersection point S. Subsequently, the melted closure material  209  flows at least partially into the opening O 2 , in which it subsequently resolidifies. As a result of this, the opening O 2  is closed and the annular space  3  is separated spatially from the process chamber  201 . For fusing of the material  209 , the laser beam preferably has a smaller energy density in comparison to the creation of the opening O 2 . This is achieved, for example, by an enlargement of the focal diameter or by beam energy reduction. 
         [0119]    Subsequently, as illustrated in  FIG. 2   d,  the closure material  209  is once again moved in its initial position away from the receiver tube  4  along the axis D and the filling device  200  can be lifted from the receiver tube  4  by releasing the fastening device  20 . 
         [0120]    In order to protect the fragile cladding tube  2  and the wall  5  from loads that are too strong owing to a fastening system  20  and thereby to protect them from potentially occurring damage, a third embodiment of the filling device  300 , illustrated in  FIG. 3   a,  can be attached to the receiver tube  4  and, in particular, to the wall  5  without additional fastening devices. For this purpose, the process chamber  301  is connected directly to the cladding tube  2  and, in particular, to the wall  5  at the contact sites between the side wall  306  and the cladding tube  2  or the wall  5 . As a result of this connection, the interior of the process chamber  301  is closed off in a gastight manner against external environmental influences. If the wall  5  and the process chamber  301  are each composed of electrically conductive material, then the connection can occur, for example, by means of the resistance welding. Alternatively, the connection can also be produced by means of a soldering method or adhesive attachment. 
         [0121]    Detailed information on the attachment of the process chamber  301  and the filling operation of the annular space  3  are discussed in connection with  FIGS. 3 b   - 3   e.    
         [0122]    The process chamber  301  in accordance with  FIG. 3 a    has, as in the case of the first two embodiments, an outlet opening  303  and an inlet opening  305 , which are each arranged at the side wall  306  of the process chamber  301 . The process chamber  301 , in turn, is connected via the outlet opening  303  to a vacuum system, which is not illustrated, with the coupling in this embodiment also occurring by means of a flange connection  33 . The interior of the process chamber  301  can be evacuated by means of the outlet opening  303 . The process chamber  301  is connected to the gas supply system  50  via the inlet opening  305 , so that the process chamber  301  can be filled with an appropriate process gas from a gas tank  51 . Further features and properties of the gas supply system  50 , the vacuum system, and the connection thereof to the process chamber  301  may be taken from the discussions in connection with the first and second embodiment. 
         [0123]    Furthermore, the process chamber  301  has a lead-through opening  304 , which is arranged at the cover wall  307  of the process chamber  301 . In order to connect the interior of the process chamber  301  to the annular space  3  of the receiver tube  4 , the filling device  300  includes a punching system  70 , by means of which a cannula  309 , which is open at both ends, can be pressed through the wall  5 . The punching system  70  has a punching rod  72 , which extends perpendicularly through the lead-through opening  304  at least partially into the interior of the process chamber  301  and is arranged movably on an axis T. In order to be able to move the punching rod  72 , it is connected to a stroke apparatus outside of the process chamber  301 , which is not illustrated in  FIG. 3   a.  When a force is imposed on the punching rod  72  along the axis T by the stroke apparatus, said punching rod can be pushed into the interior of the process chamber  301  and then retracted to its initial position. 
         [0124]    In the interior of the process chamber  301 , the punching rod  72  is completely surrounded by a seal  74  in the form of a bellows. This seal  74  seals the interior of the process chamber  301  against the lead-through opening  304  and extends from the cover wall  307  to the punching head  73 . In this case, the punching head  73  forms the end of the punching rod  72  facing away from the cover wall  307  and arranged inside of the process chamber  301 . 
         [0125]    The cannula  309  is reversibly fastened at this punching head  73 . The cannula  309  has two ends  310  and  311 . The end  310  forms the connecting end  310  between the cannula  309  and the punching head  73  and the end  311  forms the puncturing end  311 , with which the cannula  309  is forced through the wall  5 . The connecting end  310  is flattened for a loss-free transmission of force between the cannula  309  and the punching head  73 , whereas the puncturing end  311  has a point for facilitated penetration of the wall  5 . 
         [0126]    A spiral spring can be arranged within the seal  74  and, when the punching rod  72  moves, produces a restoring force that acts to bring the punching system  70  back into its initial position. 
         [0127]    In the third embodiment of the filling device  300 , in addition, two lead-through openings  313 , each of them for an electrode  312 , are arranged through the side wall  306 . These electrodes  312  can move on an axis E that is perpendicular to the side wall  306 . Furthermore, the electrodes  312  are connected to a voltage source, which is not illustrated in  FIG. 3   a.  Further information on the electrodes  312  is discussed in connection with  FIG. 3   e.    
         [0128]    In  FIGS. 3 b    to  3   e,  individual steps of the filling operation of the annular space  3  of a receiver tube  4  are illustrated schematically by means of the third embodiment of the filling device  300 . 
         [0129]    Depicted in  FIG. 3 b    is the first process step of the filling operation of the annular space  3 , in which the process chamber  301  is placed onto the cladding tube  2  and, in particular, onto the wall  5 , so that the side wall  306  is in direct contact with the wall  5 . Both the process chamber  301  and the wall  5  are composed of an electrically conductive material. Subsequently, the process chamber  301  and the wall  5  are connected to the voltage source  82   a  by means of electrical wires  81   a.  The electrical wires  81   a  and the voltage source  82   a  together constitute the electrical system  80   a.  An electrical voltage generated between the side wall  306  and the wall  5  results in an electric current flowing through the connecting sites and leading, on account of Joule current heating, to welding of the process chamber  301  with the wall  5  at the connecting sites thereof. The connection thereby produced, Va, seals the interior of the process chamber  301  toward the outside in a gastight manner. Alternatively, the connection Va can be produced in a material-bonded manner by soldering or adhesive bonding. 
         [0130]    Once the connection Va has been produced, the process chamber  301  is evacuated via the outlet opening  303  by use of the vacuum pump  31  of the vacuum system  30  illustrated in  FIG. 3   c.  Once the interior of the process chamber  301  drops below a maximum pressure, the process chamber  301  can be filled optionally with a process gas from the gas tank  51  of the gas supply system  50 . Subsequently, the cannula  309  is pressed through the wall  5  by means of the punching system  70 . For this purpose, the cannula  309  is arranged with its connecting end  310  at the punching head  73 . By means of an external stroke apparatus, the punching rod  72 , together with the cannula  309 , is caused to travel on the axis T from the initial position in the direction of the receiver tube  4 . This movement occurs preferably until the puncturing end  311  has penetrated completely into the annular space  3 . In this case, the vacuum or the process gas inside of the process chamber  301  prevents contamination of the annular space  3  when the cannula  309  punctures the wall  5 . 
         [0131]    Because the seal  74  is connected to both the cover wall  307  and the punching head  73 , it expands during movement in the axial direction. In the process, the inner space of the process chamber  301  remains sealed from the lead-through opening  304  during the complete movement of the punching system  70 . 
         [0132]    In order to ensure a secure sliding of the cannula  309  through the wall  5 , both the cannula  309  and the wall  5  are preferably composed of metal. Metal also has the advantage of being electrically conductive and weldable, which is required for the connecting process between the cannula  309  and the wall  5  described below. The punching rod  72 , too, is composed of an electrically conductive material, with the punching rod  72  and the cannula  309  being electrically connected to each other. 
         [0133]    Once the puncturing end  311  of the cannula  309  has been pressed completely through the wall  5 , an electrical voltage is also induced between the punching system  70  and the wall  5  by means of the voltage source  82   b  and the electrical wires  81   b.  On account of the electrical contact between the punching rod  72  and the cannula  309 , this voltage leads to a flow of electrical current through the connecting site of the cannula  309  and the wall  5 , which, in turn, on account of the Joule current heating, leads to a material-bonded welded connection Vb between the cannula  309  and the wall  5  at this connecting site. Accordingly, the cannula  309  is connected to the wall  5  in a firm and fluidtight manner. 
         [0134]    The electrical system  80   b,  composed of the electrical wires  81   b  and the voltage source  82   b,  can be identical to the electrical system  80   a.  The process steps subsequent to the connection Vb produced between the cannula  309  and the wall  5  are illustrated in  FIG. 3   d.    
         [0135]    In order to produce a spatial connection between the interior of the process chamber  301  and the annular space  3 , the punching rod  72 , together with the punching head  73 , is moved away from the receiver tube  4  along the axis T, so that the initial position of the punching system  70  is reassumed. However, the cannula  309  remains connected to the wall  5 . As a result, the connecting end  310  of the cannula lies freely in the interior of the process chamber  301  and the puncturing end  311  lies freely in the annular space  3  of the receiver tube  4  and, in consequence thereof, the cannula  309  forms a spatial passage between the process chamber  301  and the annular space  3 . Once the process gas is introduced from the gas tank  51  into the process chamber  301 , the process gas flows from the process chamber  301  through the cannula  309  into the annular space  3  of the receiver tube  4  on account of the now prevailing pressure gradient from the process chamber  301  into the annular space  3 . This gas flow G occurs until the intended pressure prevails in the annular space  3 , an intended gas quantity flows into the annular space  3 , or an intended flow time has expired. 
         [0136]    After the annular space  3  has been filled with the process gas, the cannula  309  is closed again, this being illustrated in  FIG. 3   e.    
         [0137]    In order to make possible this closing, the two opposite-lying electrodes  312  in the side wall  306  of the process chamber  301  come into use. They are mounted on an axis E so that they can shift in place and extend through the lead-through openings  313  from outside into the interior of the process chamber  301 . In this case, the lead-through openings  313  are preferably vacuum lead-throughs. 
         [0138]    The electrodes  312  are connected via electrical wires  81   c  to an electrical voltage source  82   c,  by means of which an electrical voltage can be generated between the two electrodes  312 . The electrical wires  81   c,  together with the voltage source  82   c,  constitute the electrical system  80   c.  This system  80   c  can be identical to the electrical systems  80   b  and/or  80   a.    
         [0139]    In order to close the cannula  309 , the electrodes  312  are moved toward the cannula  309  on the axis E until they contact each other. The contact sites are located in this case preferably near to the connecting ends  310  of the cannula  309 . Subsequently, an electrical voltage is applied at the electrodes  312 . On account of the Joule current heating, this voltage leads to an increase in temperature and ultimately to a softening of the cannula  309  at the contact sites between the cannula  309  and the electrodes  312 . The end  310  of the cannula  309  can thus be deformed by an imposed force. Once the cannula  309  has attained a viscosity at the contact sites to the electrodes  312  that is suitably high for deformation, the electrodes  312  are moved further toward each other on the axis E. This occurs until the opposite-lying walls of the cannula  309  touch each other. When an appropriately high pressure of the electrodes  312  on the wall of the cannula  309  exists, a material-bonded welded connection Vc is finally formed and separates the annular space  3  once again from the interior of the process chamber  301  in an airtight manner. 
         [0140]    Accordingly, the annular space  3  of the receiver tube  4  is filled with process gas and once again closed off against external influences in an airtight manner. 
         [0141]    A fourth embodiment of the filling device  400  is illustrated in  FIG. 4   a.  This device  400  also has a process chamber  401 , which is arranged directly at the receiver tube  4  in an airtight manner. The arrangement in this case can occur by means of a fastening system  20 , for example, as is illustrated in  FIG. 1   a,  or by means of an irreversible connection, as is illustrated in  FIG. 3 a    or  4   a.    
         [0142]    The process chamber  400  has, as in the case of the two embodiments  200  and  300 , an outlet opening  403  and an inlet opening  405 , each of which is arranged at the side wall  406  of the process chamber  401 , with the openings  403  and  405  lying opposite to each other. The process chamber  401 , in turn, is connected to a vacuum system  30  via the outlet opening  403 , with the coupling occurring in this embodiment as well by means of a flange connection  33 . The process chamber  401  is connected to the gas supply system  50  via the inlet opening  405 . Accordingly, the process chamber  401  can be evacuated and filled with a process gas. 
         [0143]    Further features and properties of the gas supply system  50 , the vacuum system  30 , and the connection thereof to the process chamber  401  may be taken from the discussions in connection with the second and third embodiment. 
         [0144]      FIG. 4 b    depicts a cutout illustration of  FIG. 4   a.  As can be seen from this figure, the process chamber  401  has a lead-through opening  404 , which is arranged at the cover wall  407 . In order to connect the interior of the process chamber  401  to the annular space  3  of the receiver tube  4 , the filling device  400  contains a punching system  70 , by means of which a cannula  409  that is open at both ends can be pressed through the wall  5 . 
         [0145]    The punching system  70  has the same properties and features as already discussed in connection with  FIG. 3   a.    
         [0146]    However, the cannula  409  differs from the cannula  309  of the third embodiment of the filling device  300 . The cannula  409  has two different portions  414  and  415 . The portion  414  represents the closure portion  414  and the portion  415  represents the puncturing portion  415 , with the diameter of the closure portion  414  being greater than the diameter of the puncturing portion  415 . Furthermore, the closure portion  414  comprises the connecting end  410 , by way of which the cannula  409  is connected to the punching head  73  of the punching system  70 . Located at the bottom end of the puncturing portion  415  is the puncturing end  411  of the cannula  409 , with which the wall  5  is penetrated, for example. A closure material  417  is arranged, in addition, in the cannula  409  and, in particular, in the closure portion  414 . This closure material  417  is arranged in such a way that, initially, a spatial passage exists between the two ends  410  and  411  and the function of the cannula is ensured. 
         [0147]    Furthermore, the closure material  418  is arranged outside of the cannula  409  in the connecting region between the closure portion  414  and the puncturing portion  415 . The closure materials  417  and  418  can be identical or different. If both the closure material  417  and the closure material  418  are each composed of a solder, then the closure material  417  preferably has a higher melting temperature than the material  418 . 
         [0148]    In order to heat and melt the closure materials  417  and  418 , the process chamber  401  has a heating apparatus  416  in the form of a spiral heating element or an induction coil, which is located in the interior of the process chamber  401 . The heating apparatus  416  is arranged in such a way that the cannula  409  extends at least partially through it. 
         [0149]    The filling process of the annular space  3  of a receiver tube  4  will be discussed in connection with  FIGS. 4 c    to  4   e.    
         [0150]    The first process steps of putting in place the process chamber  401 , connecting the process chamber  401  to the wall  5 , and subsequently evacuating the process chamber  401  and filling it with a process gas correspond to the process steps that were discussed in connection with  FIG. 3   b.    
         [0151]    After the process chamber  401  is placed on the wall  5  of the receiver tube  4  in a gastight manner, evacuated, and optionally already filled with the process gas, the cannula  409  is pressed through the wall  5  by means of the punching system  70 . This step is illustrated in  FIG. 4   c.  For this purpose, the cannula  409  is arranged with its connecting end  410  at the punching head  73 . By means of an external stroke apparatus, which is not illustrated in  FIG. 4   c,  the punching rod  72 , together with the cannula  409 , is caused to travel on the axis T from the initial position in the direction of the receiver tube  4 . This movement occurs until the puncturing end  411  has penetrated preferably completely into the annular space  3  and the closure material  418  is in direct connection between the closure portion  414  of the cannula  409  and the wall  5 . In the process, the cannula  409  punctures the wall  5  only with its puncturing portion  415 . The closure portion  414  remains completely inside of the process chamber  401 . 
         [0152]    Preferably, the closure material  418  is formed by a thermally resistant adhesive. The closure material  418  can alternatively be formed from a solder, which, after the cannula  409  has punctured the wall  5  is fused by means of the heating apparatus  416 . After subsequent solidification, it fixes the cannula  409  in place at the wall  5  and seals off the connecting site. 
         [0153]    The vacuum or process gas inside of the process chamber  401  prevents contamination of the annular space  3  when the cannula  409  punctures the wall  5 . 
         [0154]    Because the seal  74  is connected to both the cover wall  407  and the punching head  73 , it expands during the movement. The inner space of the process chamber  401  is therefore sealed off from the lead-through opening  404  during the complete movement of the punching system  70 . 
         [0155]    The process steps that occur subsequent to puncture of the wall  5  by means of the cannula  409  are illustrated in  FIG. 4   d.    
         [0156]    In order to produce a spatial connection between the interior of the process chamber  401  and the annular space  3 , the punching rod  72 , together with the punching head  73 , is moved away from the receiver tube  4  along the axis T, so that the initial position of the punching system  70  is assumed once again. However, the cannula  409  continues to be connected to the wall  5  in a material-bonded manner. As a result, the connecting end  410  of the cannula  409  lies freely in the interior of the process chamber  401  and the puncturing end  411  lies freely in the annular space  3  of the receiver tube  4 . The cannula  409  forms a spatial passage between the process chamber  401  and the annular space  3 . The process gas flows from the gas tank  51  into the process chamber  401  on account of the prevailing pressure gradient in this direction. This gas flow G occurs until the intended pressure prevails in the annular space  3 , an intended gas quantity flows into the annular space  3 , or an intended flow time has expired. 
         [0157]    After the annular space  3  has been filled with process gas, the cannula  409  is closed again, this being illustrated in  FIG. 4   e.    
         [0158]    For this purpose, the closure material  417  arranged inside of the closure portion  414  is also composed preferably of a solder, which is fused by means of the heating apparatus  416 . Once the closure material  417  has been fused by the heating apparatus  416 , it flows at least partially into the puncturing portion  415  and closes the cannula  409 . 
         [0159]    If both the closure material  417  and the closure material  418  are each composed of a solder, then either it needs to be ensured that the closure material  417  does not run into the closure portion  414  already during fusion for the purpose of fixing the cannula in place at the wall  5 . For this reason, it preferably has a higher melting temperature than the closure material  418 . Otherwise, when the two closure materials are identical, both materials are fused one time only after filling, as a result of which both the connecting site between the cannula and the wall and the lead-through opening in the cannula are sealed in one process step. 
         [0160]    After subsequent solidification of the closure materials, the annular space  3  and the process chamber  409  exist again spatially separated from each other and the filling process of the annular space  3  with a process gas is terminated. 
         [0161]    A fifth embodiment of the filling device  500  is illustrated in lengthwise section through the receiver tube in  FIG. 5   a.    FIG. 5 b    shows an enlarged cutout. The wall  5  has a glass-metal transition element  6  known from prior art, an expansion compensation device  7 , and further connecting elements  8 . 
         [0162]    The filling apparatus  500  has a process chamber  501 , which is arranged directly on the wall  5  in a gastight manner. Furthermore, the filling device  500  has a support system  520 , which is arranged at the cladding tube  2  in a manner that, for example, is vibration dampened. This support system  520  is connected to the process chamber  501  by means of two corrugated hoses  526  and  527  and serves for decoupling any mechanical load due, for example, to a vacuum system  30  or a laser system  40  from the process chamber  501 . 
         [0163]    The support system  520  has two valves  525  and  529 . It is possible by means of these valves  525  and  529  to connect the support system  520 , on the one hand, to a vacuum system  30  for evacuating the support system  520  and the process chamber  501  and, on the other hand, to a gas supply system  550  for filling the support system  520  and the process chamber  501  with a process gas and to disconnect them at will. 
         [0164]    A getter  551  is placed in the gas supply system  550 . Zirconium-based getters  551  absorb air or hydrogen, but not the process gas xenon that is preferably used. Accordingly, the getter  551  serves to keep the support system  520  and the process chamber  501  free of air from the surrounding or hydrogen from the annular space  3  of the receiver tube  4  when the vacuum system  30  has been separated by closing of the valve  529 . 
         [0165]    Furthermore, the support system  520  has a sensor  521 , by means of which state data of the support system  520  and thus of the process chamber  501  can be determined. Thus, for example, the existing pressure, the gas composition, the temperature, and other characteristic parameters of the support system  520  can be determined. 
         [0166]    The support system  520  further has a support arm  522 , at which the laser system  40  and, in particular, the laser head  43  are arranged. By means of the corrugated hose  526 , the process chamber  501  is connected to the support arm  522  and thus also to the laser head  43 . In this case, the support arm  522  and the laser head  43  are arranged in such a way that the laser beam emerging from the laser head  43  passes along the central axis in the lengthwise direction through the process chamber  501  and impinges perpendicularly on the wall  5 . 
         [0167]    It can further be seen in  FIG. 5 b    that, in the process chamber  501  at the side that faces the wall  5 , a protective glass  530  and, at the side that faces the laser head  43 , a window  531  are arranged. Both the window  531  and the protective glass  530  are optically transparent to the laser beam. In addition, the window  531  is installed in a gastight manner in the process chamber  501 , so that only the laser beam and no other foreign matter, such as, for example, dust or gases, can enter the process chamber  501 . 
         [0168]    By contrast, the protective glass  530  is arranged in the process chamber  501  in such a way that, during laser beam drilling, metal that has vaporized out of the drilled hole, can be trapped, but a subsequent evacuation of the annular space  3  continues to be possible. Consequently, the protective glass  530  is arranged reversibly in the process chamber  501  and/or is designed to be permeable to gas. 
         [0169]    Illustrated in  FIG. 6 a    is a sixth embodiment of the filling device  600 . This filling device  600  is identical to the filling device  500  apart from two differences. As first difference, the getter  641  is arranged in a sight glass  640 . This sight glass  640  is connected to the support system  620  and makes possible a gas exchange between the sight glass  641  and the support system  620 . For example, the getter  641  is formed by a vaporization getter. Such a vaporization getter is formed by a precipitate of barium on the inner side of the sight glass  640 . The barium precipitate serves, on the one hand, to absorb undesired gases and, on the other hand, however, it also alters its metallic luster appearance when it has absorbed a greater quantity of gases. It is thus possible with the vaporization getter  641  in the sight glass  640  to determine whether, during the filling operation, unallowable high quantities of air or other reactive gases have penetrated into the process chamber  601  or the support system  620 . 
         [0170]    As second difference to the filling device  500 , the protective glass  630  can rotate and is arranged inside of the process chamber  601 . This is discussed in greater detail below on the basis of the enlarged cutout in  FIG. 6   b.    
         [0171]    The process chamber  601 , in analogy to the process chamber  501 , is connected to the support system  620  by means of two corrugated hoses  626  and  627 . The process chamber  601 , in analogy to the process chamber  501  also has a window  631  with the same properties as the window  531 . The difference with respect to the process chamber  501  consists, however, as already mentioned, in its ability to rotate and in the arrangement of the protective glass  630  inside of the process chamber  601 . The protective glass  630  is connected via a rotary shaft  633  to a motor  634 , which can rotate the protective glass  630  around the lengthwise axis of the rotary shaft  633 . In this case, the motor  634  is preferably arranged on the support arm  622 . Alternatively, instead of the motor  634 , it is also possible to provide a handle so that the protective glass  630  can be rotated manually around the lengthwise axis of the rotary shaft  633 . 
         [0172]    The rotatable protective glass  630  is also optically transparent to the laser beam and serves to trap metal that has vaporized from the drilled hole during laser drilling and to keep it away from the window  631 . After the drilled hole has been produced, the protective glass  630  can be rotated further, so that the laser beam again can pass through a glass area that has not been subjected to vapor deposition. Alternatively, the protective glass  630  can also be segmented or perforated, so that, after it has rotated, the laser beam impinges on a free zone, that is, no longer passes through the material of the protective glass. 
         [0173]    Alternatively to a rotational movement, a sliding movement can also occur in order to bring a window portion that has not been subjected to vapor deposition or is free into the path of the laser beam. In addition, the protective glass  630  can alternatively be pivoted (swung out) around from the beam path around an axis that is directed perpendicular to the plane of the drawing. 
         [0174]    In order to evacuate the annular space  3  in the fifth and sixth embodiment and to fill it with a process gas, the following method steps are carried out. The description of the method refers, by way of example, to the sixth embodiment. 
         [0175]    First of all, the process chamber  601  is connected to the support system  620  by means of the corrugated hoses  626  and  627 . Subsequently, the gas supply system  650  and the sensor  621  are also connected to the support system  620 . After this, the process chamber  601  is fastened at the wall  5  and the support system  620  is fastened at the cladding tube  2  of the receiver tube  4 . After the vacuum system  30  as well has been attached to the support system  620 , both the support system  620  and the process chamber  601  are evacuated. This occurs until a pressure of less than 10 −3  mbar is registered by the sensor  621 . 
         [0176]    Subsequently, the getter  640  is connected to the inner space of the support system  620 , by opening a valve  642  between the sight glass  641  and the support system  620 . After this, the valve  629  is shut, as a result of which the vacuum system  30  exists separated from the support system  620 . In order to produce the opening through the wall  5 , the laser head  43  is fastened to the support arm  622 . At the start of the laser drilling through the wall  5 , the getter  640  must have a metallic luster, which reveals that no contamination of the process chamber  601  or of the support system  620  has occurred during the preceding process steps. Subsequently, the actual drilling of the hole  01  through the wall  5  occurs by means of the laser beam. 
         [0177]    For filling of the annular space  3  with the process gas, the values  624  and  625  are opened, so that the process gas, such as, for example, xenon, flows from the gas supply system  650  into the annular space  3  until pressure compensation is reached at approximately 10 mbar. The pressure is measured, for example, by means of the sensor  621 . For further monitoring that, during the filling operation, no entry of air into the support system  620  or the process chamber  601  has taken place, the getter  640  can continue to be inspected for visible changes. For subsequent closing of the opening in the wall  5 , the focal point diameter of the laser beam is widened by means of the optical system  44  and the opening in the wall  5  is again irradiated. For monitoring whether the opening has also been successfully closed, visual inspection occurs on the one hand and a lowering of the hydrogen partial pressure can be registered by means of the sensor  621  on the other hand. For a third monitoring possibility, the valve  629  can be opened once again, as a result of which, on account of the vacuum system  30 , a rapid drop in pressure occurs and a final pressure of approximately 10 −3  mbar ought to be achieved. If this final pressure is not achieved or is achieved only very slowly, possibly gas could flow back from the annular space  3  into the process chamber  601 , which would point to a leaking closure of the opening. If the annular space  3  has been filled with the process gas successfully, then the process chamber  601  and the support system  620  are ventilated and all components of the filling device  600  are dismantled form the receiver tube  4 . 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE SIGNS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 absorber tube 
               
               
                   
                  2 
                 cladding tube 
               
               
                   
                  3 
                 annular space 
               
               
                   
                  4 
                 receiver tube 
               
               
                   
                  5 
                 wall 
               
               
                   
                  6 
                 glass-metal transition element 
               
               
                   
                  7 
                 expansion compensation device 
               
               
                   
                  8 
                 connecting element 
               
               
                   
                  20 
                 fastening system 
               
               
                   
                  21 
                 clamp 
               
               
                   
                  22 
                 fastener 
               
               
                   
                  30 
                 vacuum system 
               
               
                   
                  31 
                 vacuum pump 
               
               
                   
                  32 
                 vacuum hoses 
               
               
                   
                  33 
                 flange connection 
               
               
                   
                  40 
                 laser system 
               
               
                   
                  41 
                 laser source 
               
               
                   
                  42 
                 light guide 
               
               
                   
                  43 
                 laser head 
               
               
                   
                  44 
                 optical system 
               
               
                   
                  45 
                 focusing unit 
               
               
                   
                  46 
                 flange connection 
               
               
                   
                  50 
                 gas supply system 
               
               
                   
                  51 
                 gas tank 
               
               
                   
                  52 
                 flange connection 
               
               
                   
                  70 
                 punching system 
               
               
                   
                  72 
                 punching rod 
               
               
                   
                  73 
                 punching head 
               
               
                   
                  74 
                 seal 
               
               
                   
                  80a, b, c 
                 electrical system 
               
               
                   
                  81a, b, c 
                 electrical wires 
               
               
                   
                  82a, b, c 
                 voltage source 
               
               
                   
                 100 
                 first embodiment of the filling device 
               
               
                   
                 101 
                 process chamber 
               
               
                   
                 102 
                 seal 
               
               
                   
                 103 
                 outlet opening 
               
               
                   
                 104 
                 lead-through opening 
               
               
                   
                 105 
                 inlet opening 
               
               
                   
                 106 
                 side wall 
               
               
                   
                 107 
                 cover wall 
               
               
                   
                 200 
                 second embodiment of the filling 
               
               
                   
                   
                 device 
               
               
                   
                 201 
                 process chamber 
               
               
                   
                 202 
                 seal 
               
               
                   
                 203 
                 outlet opening 
               
               
                   
                 204 
                 lead-through opening 
               
               
                   
                 205 
                 inlet opening 
               
               
                   
                 206 
                 side wall 
               
               
                   
                 207 
                 cover wall 
               
               
                   
                 208 
                 lead-through opening 
               
               
                   
                 209 
                 closure material 
               
               
                   
                 300 
                 third embodiment of the filling device 
               
               
                   
                 301 
                 process chamber 
               
               
                   
                 303 
                 outlet opening 
               
               
                   
                 304 
                 lead-through opening 
               
               
                   
                 305 
                 inlet opening 
               
               
                   
                 306 
                 side wall 
               
               
                   
                 307 
                 cover wall 
               
               
                   
                 309 
                 cannula 
               
               
                   
                 310 
                 connecting end of the cannula 
               
               
                   
                 311 
                 puncturing end of the cannula 
               
               
                   
                 312 
                 electrode 
               
               
                   
                 313 
                 lead-through opening 
               
               
                   
                 400 
                 fourth embodiment of the filling device 
               
               
                   
                 401 
                 process chamber 
               
               
                   
                 403 
                 outlet opening 
               
               
                   
                 404 
                 lead-through opening 
               
               
                   
                 405 
                 inlet opening 
               
               
                   
                 406 
                 side wall 
               
               
                   
                 407 
                 cover wall 
               
               
                   
                 409 
                 cannula 
               
               
                   
                 410 
                 connecting end of the cannula 
               
               
                   
                 411 
                 puncturing end of the cannula 
               
               
                   
                 414 
                 closure portion 
               
               
                   
                 415 
                 puncturing portion 
               
               
                   
                 416 
                 heating apparatus 
               
               
                   
                 417 
                 closure material 
               
               
                   
                 418 
                 closure material 
               
               
                   
                 500 
                 fifth embodiment of the filling device 
               
               
                   
                 501 
                 process chamber 
               
               
                   
                 502 
                 seal 
               
               
                   
                 503 
                 inlet/outlet opening 
               
               
                   
                 504 
                 lead-through opening 
               
               
                   
                 520 
                 support system 
               
               
                   
                 521 
                 sensor 
               
               
                   
                 522 
                 support arm 
               
               
                   
                 524 
                 valve 
               
               
                   
                 525 
                 valve 
               
               
                   
                 526 
                 corrugated hose 
               
               
                   
                 527 
                 corrugated hose 
               
               
                   
                 528 
                 corrugated hose 
               
               
                   
                 529 
                 valve 
               
               
                   
                 530 
                 protective gas 
               
               
                   
                 531 
                 window 
               
               
                   
                 550 
                 gas supply system 
               
               
                   
                 551 
                 getter 
               
               
                   
                 600 
                 sixth embodiment of the filling device 
               
               
                   
                 601 
                 process chamber 
               
               
                   
                 602 
                 seal 
               
               
                   
                 603 
                 inlet/outlet opening 
               
               
                   
                 604 
                 lead-through opening 
               
               
                   
                 620 
                 support system 
               
               
                   
                 621 
                 sensor 
               
               
                   
                 622 
                 support arm 
               
               
                   
                 624 
                 valve 
               
               
                   
                 625 
                 valve 
               
               
                   
                 626 
                 corrugated hose 
               
               
                   
                 627 
                 corrugated hose 
               
               
                   
                 628 
                 corrugated hose 
               
               
                   
                 629 
                 valve 
               
               
                   
                 630 
                 protective gas 
               
               
                   
                 631 
                 window 
               
               
                   
                 633 
                 rotary shaft 
               
               
                   
                 634 
                 motor 
               
               
                   
                 640 
                 sight glass 
               
               
                   
                 641 
                 getter 
               
               
                   
                 642 
                 valve 
               
               
                   
                 650 
                 gas supply system 
               
               
                   
                 O1 
                 opening of the first embodiment 
               
               
                   
                 O2 
                 opening of the second embodiment 
               
               
                   
                 D 
                 axis of the closure material 
               
               
                   
                 E 
                 axis of the electrode 
               
               
                   
                 G 
                 gas flow 
               
               
                   
                 L1 
                 axis of the laser beam of the first 
               
               
                   
                   
                 embodiment 
               
               
                   
                 L2 
                 axis of the laser beam of the second 
               
               
                   
                   
                 embodiment 
               
               
                   
                 S 
                 intersection point of the axes D and L2 
               
               
                   
                 T 
                 axis of the punching rod 
               
               
                   
                 Va 
                 material-bonded connection 
               
               
                   
                 Vb 
                 material-bonded connection 
               
               
                   
                 Vc 
                 material-bonded connection