Abstract:
An in-situ plasma cleaning device (PCD) performs an atomic surface cleaning process to remove contaminants and/or to modify the cylindrical surfaces of both the target and substrate. The atomic cleaning process utilizes a plasma generated locally within the in-situ plasma cleaning device with suitable properties to clean both the target and substrate cylindrical surfaces either concurrently or separately. Moreover, the in-situ plasma cleaning device is designed to traverse the length of the target and the substrate cylindrical surfaces during the cleaning process.

Description:
FEDERAL RESEARCH STATEMENT 
   The inventions described herein may be manufactured, used, and licensed by, or for the U.S. Government for U.S. Government purposes. 
   BACKGROUND OF INVENTION 
   Field of the Invention 
   The present invention relates in general to the field of atomically cleaned surface preparation prior to surface coating, and particularly relates to a new method of removal and/or modification of the contaminant and/or substrate material for preparing long cylindrical surfaces prior to surface coating by cylindrical magnetron sputtering (CMS). More specifically, the invention features an in-situ plasma cleaning device (PCD) that enables the removal and collection of material from either or both target and substrate cylindrical surfaces. Additionally, the ability for the in-situ PCD to be stowed inside the cleaning cylindrical chamber for the application of the CMS coating eliminates the need for exposing the system to ambient atmospheric environment which would introduce contamination that would result in a less than desirable deposited coating. 
   BACKGROUND OF THE INVENTION 
   Cylindrical surfaces frequently undergo various types of coating to achieve certain functional or design purposes. For example, a cylindrical surface may receive a coating treatment to enhance its wear protection or to restore its dimension to the original specification. Depending on the degree of the fineness of the coating as required in a certain application, the cylindrical surface in general must undergo a surface preparation process of varying degree of complexity prior to receiving the coating. In addition to the fineness of the coating, the size of the cylindrical surface also dictates the method of surface preparation. For example, in some specialized cases involving long cylindrical surfaces, the method of surface preparation becomes highly specialized for this particular type of system. 
   In general, the surface preparation involves the removal of contaminants from the cylindrical surfaces for disposal. Upon the removal of the contaminants, a coating process is then applied onto the cleaned surfaces for depositing the coating material to a prescribed fineness and dimension. Currently, there exist many different coating processes designed for various different applications. One such coating process commonly used for cylindrical surfaces utilizes a method of cylindrical magnetron sputtering (CMS) for depositing the coating material. 
   In general, the cylindrical magnetron sputtering is an electrical vacuum based vapor deposition process that is used to sputter, or deposit, the coating material from a cylindrical source, known as a target, onto another cylindrical surface, called a substrate. Generally, the target and the substrate are concentric cylinders. One arrangement would be such that the target is an inner solid cylinder or cylindrical tube and the substrate is an outer cylindrical tube or barrel. The converse arrangement also applies. 
   In certain applications involving long cylindrical surfaces such as gun or cannon barrels, the former arrangement is much more prevalent than the latter. That is, the target cylinder, typically in these applications, is positioned inside and concentric to the substrate cylindrical barrel. 
   The state of the art in the cylindrical magnetron sputtering systems for preparing long cylindrical surfaces prior to coating is to clean both the target and substrate surfaces onto a collector shield, or a plurality of collector shields. Thereupon, the collector shields are transferred to another location for further processing. 
   In general, the collector shields are formed of cylindrical surfaces that fit inside the inner wall of the substrate cylindrical tube with high degree of precision. The collector shields typically span a substantial length of the substrate cylindrical barrel. In long cylindrical systems, these collector shields would need a large amount of physical space for storage. Alternatively, they would need to be removed from the system for relocation, thus necessitating an opening of the substrate cylindrical barrel, which is normally sealed during the surface preparation. As a result of exposure to ambient atmospheric environment, contaminants would be reintroduced back into the cylindrical systems, thereby compromising the cleaning process. 
   In a conventional process, in order to attempt to reduce new contamination from the atmosphere, a clean gas is usually flushed through the substrate cylindrical barrel upon opening. In spite of gas flushing, contamination of cylindrical surfaces still occurs, thus leading to a compromise in the performance of the vacuum system of the ensuing cylindrical magnetron sputtering process. As a result, coating quality and adhesion of the target material onto the substrate cylindrical surface may be significantly degraded. 
   Thus, there is currently an unfulfilled need for an improved method of cylindrical surface preparation that will perform the process of cleaning long cylindrical surfaces satisfactorily. Recognizing that the source of recontamination is caused by the opening of the cylindrical system in between processes to remove and reposition the collector shields, the improved method preferably would not rely on the process of removal and relocation of the collector shields from the substrate cylindrical barrel in between processes, thereby eliminating the source of recontamination. 
   SUMMARY OF INVENTION 
   It is a feature of the present invention to provide an in-situ plasma cleaning device (PCD) for performing an atomic surface cleaning process to remove contaminants and/or modify the cylindrical surfaces of both the target and substrate. According to the present invention, the atomic cleaning process utilizes a plasma generated locally within the in-situ plasma cleaning device with suitable properties to clean both the target and substrate cylindrical surfaces at the same time or separately. Moreover, the in-situ plasma cleaning device is designed to traverse the length of the target and the substrate cylindrical surfaces during the cleaning process. Further novelties of the present invention are enumerated as follows: 
   1. The in-situ plasma cleaning device is a self-contained unit that is designed to perform cleaning and be stowed in-situ, when not needed, within the long cylindrical system without requiring the system to be open to the ambient atmospheric environment during the cleaning process to remove the collector shields, as in the case with the conventional process. 
   2. The in-situ plasma cleaning device is comprised of a plurality of target and substrate cleaning assemblies wherein a generally axially directed magnetic field is individually provided for the local generation of the plasma for cleaning the cylindrical surface within each cleaning assembly. Each cleaning assembly incorporates a collector shield opposing to the cylindrical surface to be cleaned for collecting contaminants and by-product material during the cleaning operation. 
   3. The in-situ plasma cleaning device is of a modular design allowing the use of a combination of one or more target and substrate cleaning assemblies in any order. The target and substrate cleaning assemblies are designed to properly interface for a modular interconnection. Thus, there are several variations of the in-situ plasma cleaning device, depending on the cylindrical magnetron sputter cleaning or surface modification process involved. Notwithstanding, the basic function of the in-situ plasma cleaning device remains the same. 
   The in-situ plasma cleaning device of the present invention affords a number of advantages over the conventional processes. One such clear advantage is the ability for the in-situ plasma cleaning device to perform cleaning of cylindrical surfaces in a closed volume process that effectively eliminates the source of recontamination as is in the conventional process. 
   A further advantage is the ability to tune the locally generated plasma to attain suitable properties for different target and substrate materials. As a result, the adhesion and coating quality is substantially improved over that of a conventional process. 
   The modular design of the in-situ plasma cleaning device provides yet another advantage in that the in-situ plasma cleaning device can be adapted to any particular application involving long cylindrical surfaces by simply building the device from a suitable number of target and substrate cleaning assemblies. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein: 
       FIG. 1  illustrates a long cylindrical system comprising of a target cylindrical tube and a substrate cylindrical barrel, and an in-situ plasma cleaning device made according to a preferred embodiment of the present invention; 
       FIGS. 2A-2C  are views of the in-situ plasma cleaning device of  FIG. 1  comprising of a target cleaning assembly and substrate cleaning assembly; 
       FIGS. 3A-3B  are views of a target collector shield of the target cleaning assembly of  FIG. 2 ; 
       FIGS. 4A-4B  are views of a target inner end plate of the target cleaning assembly of  FIG. 2 ; 
       FIGS. 5A-5C  are views of a target cleaning end cap assembly of the target cleaning assembly of  FIG. 2 ; 
       FIGS. 6A-6B  are views of a target cleaning end cap of the target cleaning end cap assembly of  FIG. 5 ; 
       FIGS. 7A-7C  are views of a strip support of the target cleaning end cap assembly of  FIG. 5 ; 
       FIGS. 8A-8C  are views of a plunger strip support of the target cleaning end cap assembly of  FIG. 5 ; 
       FIGS. 9A-9C  are views of a spring roller support of the target cleaning end cap assembly of  FIG. 5 ; 
       FIGS. 10A-10B  are views of a roller block of the target cleaning end cap assembly of  FIG. 5 ; 
       FIGS. 11A-11B  are views of a roller element of the roller block of  FIG. 10 ; 
       FIGS. 12A-12B  are views of a target interface plate of the target cleaning assembly of  FIG. 2 ; 
       FIGS. 13A-13B  are views of a substrate collector shield of the substrate cleaning assembly of  FIG. 2 ; 
       FIG. 14  is a cutaway view of one of the two magnet assemblies of the substrate cleaning assembly of  FIG. 2 , shown attached to the target interface plate of  FIG. 12 ; 
       FIGS. 15A-15B  are views of a Barrel Cleaner End, as labeled in  FIG. 14 , of the magnet assembly; 
       FIGS. 16A-16B  are views of a magnet unit of the magnet assembly of  FIG. 14 ; 
       FIGS. 17A-17C  are views of a narrow keeper ring of the magnet unit of  FIG. 16 ; 
       FIGS. 18A-18B  are views of a cleaner ring of the magnet unit of  FIG. 16 ; 
       FIG. 19  is a top view of a wide keeper ring of the magnet unit of  FIG. 16 ; 
       FIGS. 20A-20B  are views of a magnet keeper cap of the magnet unit of  FIG. 16 ; 
       FIGS. 21A-21B  are views of a substrate cleaning end cap of the substrate cleaning assembly of  FIG. 2 , also shown attached to the other magnet assembly of  FIG. 14 ; 
       FIGS. 22A-22B  are views of a substrate cleaning end cap of the substrate cleaning end cap assembly of  FIG. 21 ; and 
       FIG. 23  is a cross-sectional view of the in-situ plasma cleaning device, made according to an alternative embodiment of the present invention. 
   

   Similar numerals in the drawings refer to similar elements. It should be understood that the sizes of the different components in the figures might not be in exact proportion, and are shown for visual clarity and for the purpose of explanation. 
   DETAILED DESCRIPTION 
     FIG. 1  illustrates a long cylindrical system  10  comprising of an inner target cylindrical tube  12  and an outer substrate cylindrical barrel  14 . The inner target cylindrical tube  12  and the substrate cylindrical barrel  14  are generally concentric and co-located, with the inner target cylindrical tube  12  positioned inside the substrate cylindrical barrel  14 . 
   Located within the annular space  16  between the inner target cylindrical tube  12  and the substrate cylindrical barrel  14  is an in-situ plasma cleaning device  100  made according to the present invention.  FIG. 1  illustrates a preferred embodiment of the in-situ plasma cleaning device  100  of the present invention. In particular, the in-situ plasma cleaning device  100  is comprised of a plurality of target cleaning assemblies  200  and a plurality of substrate cleaning assemblies  300 , only one of each is shown in  FIG. 1 . 
   With reference to  FIG. 2 , the preferred embodiment of the in-situ plasma cleaning device  100  is shown to comprise of a target cleaning assembly  200  connected to a substrate cleaning assembly  300 . The target cleaning assembly  200  is generally comprised of a target collector shield  202 , a target cleaning end cap assembly  204 , and a target interface plate  206 , as referenced in  FIGS. 3 to 12  (which may also be referred to as a top cap). The substrate cleaning assembly  300  is connected to the target cleaning assembly  200  via the target interface plate  206 . The substrate cleaning assembly  300  is generally comprised of a substrate collector shield  302 , two magnet assemblies  304 , and a substrate cleaning end cap assembly  306 , as referenced in  FIGS. 13 to 22  (which may also be referred to as a bottom cap in the disclosure). 
   With reference to  FIG. 3 , the target collector shield  202  is generally formed of a cylindrical tube that fits closely inside the substrate cylindrical barrel  14  with a high degree of precision. The outside diameter of the target collector shield  202  is substantially equal to the inside diameter of the substrate barrel  14  minus a very small dimensional tolerance to allow the target cleaning assembly  200  to freely move inside the substrate cylindrical barrel  14 . Be for example only, the outside diameter of the target collector shield  202  may be of a dimension of 4.6 inches. At the two distal ends of the target collector shield  202  are formed two small internal threaded areas whereon a target inner end plate  208  and the target interface plate  206  are threaded into the target collector shield  204 . 
   With reference to  FIG. 4 , the target inner end plate  208  is made of a thin circular plate having a central hole  210 . The diameter of the central hole  210  is substantially equal to the outside diameter of the target cylindrical tube  12  plus a very small tolerance to allow the target cleaning assembly  200  to freely move along the target cylindrical tube  12  without interference. Be for example only, the diameter of the central hole  210  may be of a dimension of 2.475 inches. A plurality of fastener holes  212  are formed in the target inner end plate  208 .  FIG. 4  illustrates four such fastener holes  212 . 
   With reference to  FIGS. 2 and 5 , the target cleaning end cap assembly  204  is secured to the target inner end plate  208  by a plurality of fasteners  214  through the fastener holes  212 . The fasteners  214  possess certain electrical insulating properties to isolate the target cleaning end cap assembly  204  electrically from the target inner end plate  208 . The target cleaning end cap assembly  204  is generally comprised of a target cleaning end cap  216  which is fastened to the target inner end plate  208 , a strip support  218 , a plunger strip support  220 , two spring roller supports  222 , and three roller blocks  224 . The three roller blocks  224  are attached to the plunger strip support  220  and the two spring roller supports  222  such that they are equally spaced angularly around the mid-section of the target cleaning end cap  216 . 
   With reference to  FIGS. 2 ,  5 , and  6 , the target cleaning end cap  216  is formed of a thin circular plate having a central hole  226 . The diameter of the target cleaning end cap  216  is substantially equal to the inside diameter of the substrate cylindrical barrel  14  minus a very small dimensional tolerance to allow the target cleaning assembly  200  to freely move inside the substrate cylindrical barrel  14 . The diameter of the central hole  226  is substantially equal to the outside diameter of the target cylindrical tube  12  to permit the target cleaning assembly  200  to freely translate along the target cylindrical tube  12 . A plurality of fastener holes  228  are formed in the target cleaning end cap  216 , such that their dimensions and locations match those of the fastener holes  212  of the target inner end plate  208 . 
     FIG. 6  illustrates two such fastener holes  228 . Four sets of smaller fastener holes  230 ,  232 ,  234 , and  236  are also formed in the target cleaning end cap  216  to provide means of connection of the strip support  218 , the plunger strip support  220 , and the two spring roller supports  222 , respectively, to the target cleaning end cap  216 . 
   With specific reference to  FIG. 7 , the strip support  218  is generally comprised of a strip support base  238  and two strip support devises  240 . The strip support base  238  is generally of a rectangular shape with a plurality of fastener holes  242  formed in the strip support base  238  at the two distal ends. The fastener holes  242  are generally of the same dimensions and locations as those of the fastener holes  230  of the target cleaning end cap  216 . A rectangular profile recess  244  is formed on the bottom of the strip support base  238 . The two strip support devises  240  are generally constructed of thin rectangular tabs that are secured to or integrally formed on and perpendicularly to the top of the strip support base  238 . A circular hole  246  is formed on each of the strip support devises  240 . 
   With further reference to  FIG. 5 , the strip support  218  is secured to the target cleaning end cap  216  via fasteners  248  through the fastener holes  230  and  242 . 
   With specific reference to  FIG. 8 , the plunger strip support  220  is generally comprised of a plunger strip support base  250  and two plunger strip support devises  252 . The plunger strip support base  250  is generally formed of a rectangular shape. Extending from either side of the plunger strip support base  250  are two small rectangular tabs  256  wherein two fastener holes  258  are formed. The two fastener holes  258  are generally of the same dimensions and locations as those of the fastener holes  232  of the target cleaning end cap  216 . A rectangular profile recess  260  is formed on the bottom of the plunger strip support base  250 . Two circular holes  262  are formed in the plunger strip support base  250  immediately above the rectangular recess  260 . The two plunger strip support devises  252  are generally constructed of thin rectangular tabs that are integrally formed on and perpendicularly to the top of the plunger strip support base  250 . A circular hole  264  is formed in each of the plunger strip support devises  252 . 
   With further reference to  FIG. 5 , the plunger strip support  220  is secured to the target cleaning end cap  216  via fasteners  266  through the fastener holes  232  and  258 , and is generally disposed diametrically opposite to the strip support  218 . One of the roller blocks  224  is fitted inside the rectangular profile recess  260  between the plunger strip support  220  and the target cleaning end cap  216 . 
   With specific reference to  FIG. 9 , the spring roller supports  222  are formed of a rectangular block  268 . Extending from either side of the rectangular block  268  are two small rectangular tabs  270  wherein two fastener holes  272  are formed. The fastener holes  272  are generally of the same dimensions as those of, and furthermore are aligned with either the fastener holes  234  and  236  of the target cleaning end cap  216 . A rectangular profile recess  274  is formed on the bottom of the rectangular block  268 . Two circular holes  276  are formed in the rectangular block  268  and are disposed immediately above the rectangular recess  274 . 
   With further reference to  FIG. 5 , the spring roller supports  222  are secured to the target cleaning end cap  216  at two locations via fasteners  278  through the fastener holes  234  and  272 , and fasteners  280  through the fastener holes  236  and  272 . Each of the roller blocks  224  is press fitted inside the rectangular profile recess  274  between the each of the spring roller support  222  and the target cleaning end cap  216 . 
   With reference to  FIG. 10 , the roller block  224  is generally comprised of a roller block base  282  and two roller block clevises  284 . The roller block base  282  are generally constructed of a rectangular shape with two oval fastener holes  286  formed therein. The fastener holes  286  are generally aligned with the locations of the fastener holes  236  of the target cleaning end cap  216 . A rectangular profile notch  288  is formed on one of the short sides of the roller block base  282 , whereupon the two roller block devises  284  are extended integrally from and perpendicularly to the roller block base  282 . A circular hole  290  is formed in each of the roller block devises  284 . 
   With reference to  FIG. 11 , a roller element  292  is formed of a solid cylinder having a small central hole  294 . Be for example only, the diameter of the roller element  292  is of a dimension of 0.375 inches. The diameter of the small central hole  294  is generally the same as the diameter of the circular holes  290  of the roller block devises  284 , and, be for example only, may be of a dimension of 0.13 inches. The width of the roller element  292  is slightly less than the spacing between the two roller block devises  284  and, be for example only, may be of a dimension of 0.156 inches. The roller element  292  is attached to the roller block  224  by a small pin inserted through the central holes  294  and the circular holes  290  of the roller block  224 , so that a small amount of clearance exists between the two roller block devises  284  and the roller element  292  so as to enable it to freely rotate. 
   With further reference to  FIG. 5 , when assembled together with the roller blocks  224  into the target cleaning end cap assembly  204 , the roller elements  292  partially extend slightly radially inward into the central hole  226  of the target cleaning end cap  216 , so that they make contact with the target cylindrical tube  12  to allow the target cleaning assembly  200  to roll along the target cylindrical tube  12 . 
   With specific reference to  FIG. 12 , the target interface plate  206  is made of a thin circular plate having a central hole  296 . The diameter of the central hole  296  is substantially equal to the outside diameter of the target cylindrical tube  12  plus a very small tolerance to allow the target cleaning assembly  200  to freely move along the target cylindrical tube  12  without interference. A plurality of fastener holes  298  are formed in the target interface plate  206 .  FIG. 12  illustrates three such fastener holes  298  equally spaced circumferentially. 
   With reference to  FIG. 13 , the substrate collector shield  302  is generally formed of a metal electrical conducting cylindrical tube that fits closely outside the target cylindrical tube  12  with a high degree of precision. The inside diameter of the substrate collector shield  302  is substantially equal to the outside diameter of the target cylindrical tube  12  plus a very small dimensional tolerance to allow the substrate cleaning assembly  300  to freely move along the target cylindrical tube  12 . Be for example only, the inside diameter of the substrate collector shield  302  may be of a dimension of 2.52 inches. At the two distal ends of the substrate collector shield  302  are formed two small external threaded areas whereon the magnet assemblies  304  are threaded into the substrate collector shield  302 . 
   With reference to  FIG. 14 , one of the magnet assemblies  304  is secured to the target interface plate  206  on the distal end of the substrate cleaning assembly  300  adjacent to the target cleaning assembly  200 , thus providing a physical connection of the target cleaning assembly  200  to the substrate cleaning assembly  300 . 
   With reference to  FIG. 21 , the substrate cleaning end cap assembly  306  is secured to the other magnet assembly  304  on the other distal end of the substrate cleaning assembly  300 . With further reference to  FIGS. 14 and 21 , the magnet assemblies  304  are generally comprised of a substrate outer end plate  308  and a magnet unit  310 . 
   With specific reference to  FIG. 15 , each of the substrate outer end plates  308  is made of a thin circular plate having a threaded central hole  312  to enable it to be threaded into the substrate collector shield  302  at one of the distal ends. The diameter of the substrate outer end plates  308  is substantially equal to the inside diameter of the substrate cylindrical barrel  14  minus a very small dimensional tolerance to allow the substrate cleaning assembly  300  to freely move inside the substrate cylindrical barrel  14 . A plurality of fastener holes  314  are formed in the substrate outer end plates  308  and generally are of the same dimensions and locations as those of the fastener holes  298  of the target interface plate  206 .  FIG. 15  illustrates three such fastener holes  314  equally spaced circumferentially. With further reference to  FIG. 14 , one of the substrate outer end plates  308  is secured to the target interface plate  206  via fasteners  356  through the fastener holes  298  and  314 . The fasteners  356  also possess a certain electrical insulating property to provide an electrical isolation of the substrate cleaning assembly  300  from the target cleaning assembly  200 . 
   With reference to  FIG. 16 , each of the magnet units  310  is further comprised of a narrow keeper ring  316 , a cleaner ring  318 , a wide keeper ring  320 , a plurality of magnets  322 , and a magnet keeper cap  324 . 
   With specific reference to  FIG. 17 , each of the narrow keeper rings  316  is formed of a thin circular ring having a rectangular cross section. A plurality of circular indentations  328  are formed on top of each of the narrow keeper rings  316 . Be for example only, 24 such circular indentations  328  may be used for each of the narrow keeper rings  316 . A plurality of fastener holes  330  are formed in each of the narrow keeper rings  316 . Be for example only,  FIG. 17  illustrates three such fastener holes  330 . 
   With reference to  FIG. 18 , each of the cleaner rings  318  is formed of a circular ring having a rectangular cross section wherein two diametral fastener holes  334  are formed. The thickness of the cleaner rings  318  is substantially greater than its radial thickness. The inside diameter of the cleaner rings  318  is substantially equal to the outside diameter of the narrow keeper rings  316  plus a very small dimensional tolerance. Similarly, the outside diameter of the cleaner rings  318  is substantially equal to the inside diameter of the substrate cylindrical barrel  14  minus a small dimensional clearance to permit the substrate cleaning assembly  300  to translate freely inside the substrate cylindrical barrel  14 . With further reference to  FIG. 16 , when assembled into the magnet units  310 , the narrow keeper rings  316  fits tightly inside and flush with the cleaner rings  318 . 
   With reference to  FIG. 19 , each of the wide keeper rings  320  is formed of a wide circular ring having a rectangular cross section. The inside diameter of the wide keeper rings  320  is substantially larger than the outside diameter of the substrate collector shield  302 . A plurality of circular indentations  338  are formed on top of each of the wide keeper rings  320  and offset towards the inside diameter of the wide keeper rings  320 . Be for example only, 24 such circular indentations  338  may be used for each of the wide keeper rings  320 . 
   The circular indentations  338  are of the same dimensions and locations as those of the circular indentations  328  of the narrow keeper rings  316 . Three sets of fastener holes  340 ,  342 , and  344  are formed in each of the wide keeper rings  320 . The fastener holes  340  are generally larger with same locations as the fastener holes  330  of the narrow keeper rings  316 , thus allowing the wide keeper rings  320  to secure to the narrow keeper rings  316  via fasteners  346  as illustrated in  FIG. 16 . The fastener holes  342  are generally of the same dimensions and locations as those of the fastener holes  334  of the cleaner rings  318 , thus allowing the wide keeper rings  320  to secure to the cleaner rings  318  via fasteners  348  as illustrated in  FIG. 16 . The fastener holes  344  are formed into the side of each of the wide keeper rings  320 . With further reference to  FIG. 16 , when assembled into the magnet units  310 , the wide keeper rings  320  are disposed oppositely to the narrow keeper rings  316  and are separated by the cleaner rings  318 . 
   With specific reference to  FIG. 16 , the magnets  322  are made of a permanent ferromagnetic material such as Alnico 8 (i.e., a material made of aluminum, nickel, and cobalt), and are generally of a cylindrical shape. The diameter of the magnets  322  is generally the same as the diameters of the circular indentations  328  and  338 . The length of the magnets  322  is defined by the separation distance between the circular indentations  328  and the circular indentations  338  when the narrow keeper rings  316 , the cleaner rings  318 , and the wide keeper rings  320  are assembled together. Be for example only, 24 such magnets  322  may be used for each of the magnet units  310 . When assembled into the magnet units  310 , the distal ends of the magnets  322  are fitted tightly inside the circular indentations  328  and  338  with the side of the magnets  322  in contact with the inside diameter of the cleaner rings  318 . 
   With reference to  FIG. 20 , each of the magnet keeper caps  324  is formed of a thin circular plate having a central hole  350 . The diameter of the magnet keeper caps  322  is substantially equal to the inside diameter of the substrate cleaning assembly  300  minus a very small dimensional tolerance to enable the substrate cleaning assembly to freely move inside the substrate cylindrical barrel  14 . Similarly, the diameter of the central hole  350  is substantially the same as the outside diameter of the substrate collector shield  302 . Two sets of fasteners  352  and  354  are formed in each of the magnet keeper caps  322 . The fastener holes  352  are of the same dimensions and locations as those of the fasteners  330  of the narrow keeper rings  316  and  340  of the wide keeper rings  320 , through which the magnet keeper caps  322  are secured to the wide keeper rings  320  via the fasteners  346 , as shown in  FIG. 16 . The fastener holes  354  are of the same dimensions and locations as those of the fasteners holes  314  of the substrate outer end plates  308 , through which the magnet keeper caps  322  are secured to the substrate outer end plates  308  via the fasteners  356  to form the magnet assemblies  304 , as illustrated in  FIG. 16 . 
   With reference to  FIG. 21 , the substrate cleaning end cap assembly  306  is secured to one of the substrate outer end plates  308  of the one of the magnet assembly  304  via a plurality of fasteners  358  through the fastener holes  314  of the substrate outer end plate  308 . The substrate cleaning end cap assembly  306  is generally comprised of a substrate cleaning end cap  360 , three spring roller supports  362 , and three roller blocks  364 . 
   With specific reference to  FIG. 22 , the substrate cleaning end cap  360  is formed of a thin circular plate having a central hole  366 . The diameter of the substrate cleaning end cap  360  is generally the same as the inside diameter of the substrate cylindrical barrel  14  minus a very small dimensional tolerance to allow the substrate cleaning assembly  200  to freely move inside the substrate cylindrical barrel  14 . Similarly, the diameter of the central hole  366  is generally the same as the outside diameter of the target cylindrical tube  12  plus a very small dimensional tolerance to permit the substrate cleaning assembly  200  to slide freely along the target cylindrical tube  14 . A plurality of fastener holes  368  are formed in the substrate cleaning end cap  216 , such that their dimensions and locations match those of the fastener holes  314  of the substrate outer end plate  308 .  FIG. 22  illustrates three such fastener holes  368 . Three sets of smaller fastener holes  370  are also formed in the substrate cleaning end cap  360  to provide a means of securing the three spring roller supports  362  to the substrate cleaning end cap  360 . 
   With further reference to  FIG. 9 , the spring roller supports  362  of the substrate cleaning end cap assembly  306  are identical in design to the spring roller supports  222  of the target cleaning end cap assembly  204 . 
   With further reference to  FIG. 10 , the roller blocks  364  of the substrate cleaning end cap assembly  306  are identical in design to the roller blocks  224  of the target cleaning end cap assembly  204 . 
   The functionality of the preferred embodiment will now be described in details in connection with  FIG. 1  in order to provide a clearer appreciation of the advantages afforded by the in-situ plasma cleaning device  100  of the present invention. 
   The target cylindrical tube  12  generally provides a source material for the cylindrical magnetron sputtering process. This source material is to be deposited onto the substrate cylindrical barrel  14  during the cylindrical magnetron sputtering process. Prior to this process, the target cylindrical tube  12  and the substrate cylindrical barrel  12  are required to undergo an atomic surface cleaning process. The atomic cleaning process is designed to remove contaminants at the atomic level from the surfaces of the target cylindrical tube  12  and the substrate cylindrical barrel  12 , thus leaving these surfaces virtually at their highest purity state for the subsequent cylindrical magnetron sputtering. 
   Referring now to  FIG. 1 , a target cleaning magnetic field  400  is generated by field producing means within the target cleaning annular space  402  between the target cylindrical tube  12  and the target collector shield  202 . The target cleaning magnetic field  400  is generally directed axially in the direction of the cylindrical centerline  600 . To enable the atomic cleaning process of the target cylindrical tube  12 , a voltage is applied across the target collector shield  202  and the target cylindrical tube  12  with the positive potential applied to the target collector shield  202  and the negative potential applied to the target cylindrical tube  12 . The presence of the target cleaning magnetic field  400  in the axial direction together with said applied voltage thus creates a plasma. The plasma generally is composed of positively charged ions and negatively charged electrons. The plasma can further be locally tuned within the target cleaning annular space  402  by adjusting the strength of the target cleaning magnetic field  400  accordingly. 
   As a result, the negative potential of the target cylindrical tube  12  generally attracts the positively charged ions in the plasma. These positively charged ions accelerate towards the target cylindrical tube  12  at a high speed and impact with the material of the target cylindrical tube  12  at an atomic level. The resulting ion bombardment thus causes particles of contaminants and, to a lesser extent, the source material of the target cylindrical tube  12  at the atomic level to separate from the surface of the target cylindrical tube  12 . With sufficient kinetic energy developed from the ion bombardment, these ejected particles of the contaminants and the source material separated from the target cylindrical tube  12  generally travel towards and therefore are deposited onto the target collector shield  202 . 
   Similarly, with reference to  FIG. 1 , the magnet assemblies  304  are configured to generate a substrate cleaning magnetic field  500  in the axial direction within the substrate cleaning annular space  502  between the substrate cylindrical barrel  14  and the substrate collector shield  302 . A voltage is applied across the substrate cylindrical barrel  14  and the substrate collector shield  302 , with the substrate cylindrical barrel  14  at a negative potential and the substrate collector shield  302  at a positive potential. The substrate cleaning magnetic field  500  together with said applied voltage then generates a plasma composed of positively and negatively charged ionized particles within the substrate cleaning annular space  502 . The plasma can further be locally tuned within the substrate cleaning annular space  502  by adjusting the strength of the substrate magnetic field  500  accordingly. 
   An electrostatic attraction force is thus created between the negatively charged substrate cylindrical barrel  14  and the positively charged ions in the plasma. Consequently, the positively charged ions generally accelerate towards the negatively charged substrate cylindrical barrel  14  at high speed and impact with the material of the substrate cylindrical barrel  14  at an atomic level. The resulting ion bombardment thus causes the particles of contaminants at the atomic level to separate from the surface of the substrate cylindrical barrel. With sufficient kinetic energy resulting from the ion bombardment, these particles of the contaminants generally travel towards and are subsequently deposited onto the positively charged substrate collector  302 . 
   A significant feature of the in-situ plasma cleaning device  100  is that the atomic surface cleaning can be performed selectively on either the substrate cylindrical barrel  14  or the target cylindrical tube  12  or both simultaneously by running each cleaner at different voltages from different power supplies, or alternatively to adjust the magnetic field&#39;s strengths so that each cleaner runs well at the same voltage thus allowing common connection of their anodes, together or to the same power supply. This feature is a significant time saving aspect of the present invention in contrast with the serial cleaning method of the conventional method involving removing and inserting different types of collector shield into the long cylindrical system  10 . 
   Moreover, a further significant feature of the present invention is the ability of the in-situ plasma cleaning device  100  to perform the atomic surface cleaning of the long cylindrical system  10  in a closed volume process. Because the target collector shield  202  and the substrate collector shield  302  are integral to the in-situ plasma cleaning device  100 , the atomic surface cleaning is generally performed with the target cylindrical tube  12  and the substrate cylindrical barrel  14  closed to the ambient atmospheric environment. As a result, the possibility of recontamination is eliminated. The resulting atomic cleaning by the in-situ plasma cleaning device  100  thus creates a very high purity state on the surfaces of the target cylindrical tube  12  and the substrate cylindrical barrel  14  to prepare them for the subsequent cylindrical magnetron sputtering. Consequently, upon the deposition of the source material from the target cylindrical tube  12  onto the substrate cylindrical barrel  14  in the area already atomically cleaned by the in-situ plasma cleaning device  100 , the quality of coating and the surface adhesion will be substantially improved over that of the conventional method. 
   Yet, another advantage of the present invention lies in the modular design of the in-situ plasma cleaning device  100 . Referring now to  FIG. 23 , an alternative embodiment of the present invention is shown. The in-situ plasma cleaning device  100 , according to the alternative embodiment, is comprised of two target cleaning assemblies alternating between a substrate cleaning assembly. Two target cleaning end caps  204  are positioned at two distal ends of the in-situ plasma cleaning device  100  to enable it to traverse along the long cylindrical system  10 . Thus, in this fashion, the in-situ plasma cleaning device may be constructed from an alternate arrangement of the target cleaning assemblies  200  and the substrate cleaning assemblies  300 . This modular design of the in-situ plasma cleaning device  100  enables it to adapt virtually to any long cylindrical system  10  having a variable length, while maintaining its ability to perform the atomic surface cleaning in a closed volume process. 
   It should be understood that the geometry, compositions, and dimensions of the elements described herein can be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications can be made when implementing the invention for a particular environment.