Abstract:
A system for characterizing high power electron beams at power levels of 10 kW and above is described. This system is comprised of a slit disk assembly having a multitude of radial slits, a conducting disk with the same number of radial slits located below the slit disk assembly, a Faraday cup assembly located below the conducting disk, and a start-stop target located proximate the slit disk assembly. In order to keep the system from over-heating during use, a heat sink is placed in close proximity to the components discussed above, and an active cooling system, using water, for example, can be integrated into the heat sink. During use, the high power beam is initially directed onto a start-stop target and after reaching its full power is translated around the slit disk assembly, wherein the beam enters the radial slits and the conducting disk radial slits and is detected at the Faraday cup assembly. A trigger probe assembly can also be integrated into the system in order to aid in the determination of the proper orientation of the beam during reconstruction. After passing over each of the slits, the beam is then rapidly translated back to the start-stop target to minimize the amount of time that the high power beam comes in contact with the slit disk assembly. The data obtained by the system is then transferred into a computer system, where a computer tomography algorithm is used to reconstruct the power density distribution of the beam.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/583,156 filed Jun. 24, 2004 by John W. Elmer, Todd A. Palmer, and Alan T. Teruya titled “Electron Beam Diagnostic for Profiling High Power Beams.” U.S. Provisional Patent Application No. 60/583,156 filed Jun. 24, 2004 and titled “Electron Beam Diagnostic for Profiling High Power Beams” is incorporated herein by this reference. 
    
    
     The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory. 
    
    
     BACKGROUND 
     1. Field of Endeavor 
     The present invention relates to electron beams and more particularly to a system for profiling high power beams. 
     2. State of Technology 
     U.S. Pat. No. 6,300,755 for enhanced modified faraday cup for determination of power density distribution of electron beams issued to John W. Elmer and Alan T. Teruya Oct. 9, 2001 provides the following state of technology information, “Electron beams are considered to be the most precise and clean method available for welding thick sections of materials. Unfortunately, electron beams suffer one critical deficiency, namely the repeatability of focusing the beam to a known power density. Without the ability to reliably reproduce the power distribution in an electron beam, weld quality cannot be guaranteed. This problem is exacerbated by the fact that many welds are made over a period of time and with different welding operators. Further complications arise when welds are developed on one machine than transferred to a different machine for production.” 
     SUMMARY 
     Features and advantages of the present invention will become apparent from the following description. Applicants are providing this description, which includes drawings and examples of specific embodiments, to give a broad representation of the invention. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this description and by practice of the invention. The scope of the invention is not intended to be limited to the particular forms disclosed and the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
     The present invention provides a system for characterizing high power electron beams at the 10 kW level and higher. This system is based on three basic considerations, (1) larger beams are produced at higher beam powers, (2) higher heat carrying capacity is needed in the diagnostic system, and (3) the potential for damage to the tungsten slit disk assembly of the system must be minimized. 
     The system for characterization of a high power beam of the present invention comprises a slit disk assembly of an electrically conductive refractory material. The slit disk assembly has at least one radial slit extending through the slit disk assembly and a slit disk assembly central hole extending through the slit disk assembly. The radial slit and the slit disk assembly central hole are positioned to receive the high power beam and allow the high power beam to pass through the radial slit and the slit disk assembly central hole. A conducting disk is located below the slit disk assembly. The conducting disk has at least one conducting disk radial slit extending through the conducting disk and a conducting disk central hole extending through the conducting disk. The conducting disk radial slit is positioned below and aligned with the radial slit in the slit disk assembly and the conducting disk central hole positioned below and aligned with the slit disk assembly central hole. The conducting disk radial slit and the conducting disk central hole are positioned to receive the high power beam and allow the high power beam to pass through the conducting disk radial slit and the conducting disk central hole. A Faraday cup assembly is located below the conducting disk and positioned to receive the high power beam that passes through the conducting disk central hole. A start-stop target is located proximate to the slit disk assembly. 
     The system for characterization of a high power beam is operated by directing the beam onto the start-stop target; directing the beam onto the slit disk assembly; translating the beam to the radial slits wherein the beam enters the radial slits and the conducting disk radial slits where it is detected at the Faraday cup assembly; and translating the beam back onto the start-stop target. 
     In one embodiment, a heat sink is positioned in proximity to the slit disk assembly, the conducting disk, and the Faraday cup assembly. In another embodiment, a system is provided for circulating a fluid, such as water through the heat sink. In one embodiment, the slit disk assembly includes a trigger probe. 
     The system for characterization of a high power beam has many uses. For example, the system for characterization of a high power beam has use for the welding of larger components, for melting and refining of metals and alloys, and for vaporizing metals for vapor deposition purposes. The high power applications may use 10 s of kWs of power. 
     The invention is susceptible to modifications and alternative forms. Specific embodiments are shown by way of example. It is to be understood that the invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the specific embodiments, serve to explain the principles of the invention. 
         FIG. 1  illustrates an embodiment of a system constructed in accordance with the present invention. 
         FIG. 2  shows additional details of the diagnostic system for high powered beams illustrated in  FIG. 1 . 
         FIG. 3  shows additional details of the diagnostic system for high powered beams illustrated in  FIG. 2 . 
         FIG. 4  shows details of another embodiment of the diagnostic system for high powered beams illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, to the following detailed description, and to incorporated materials, detailed information about the invention is provided including the description of specific embodiments. The detailed description serves to explain the principles of the invention. The invention is susceptible to modifications and alternative forms. The invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
     Referring now to the drawings and in particular to  FIG. 1 , an embodiment of a system constructed in accordance with the present invention is illustrated. The system is designated generally by the reference numeral  100 . The system  100  is an electron beam diagnostic system for profiling high power beams. The existing diagnostic system is designed to work in the 1 kW power range. The system for profiling high power beams  100  described herein can operate at power ranges in the 10 kW range and above. The diagnostic system  100  for high power beams involves three basic considerations, (1) larger beams are produced at higher beam powers, (2) higher heat carrying capacity is needed in the diagnostic system, and (3) the potential for damage to the tungsten slit disk assembly of the system must be minimized. 
     The system  100  has many uses, for example the system  100  can be used to provide high power electron beam welds of high value added components (aerospace, nuclear industries), electron beam melting for alloy refinement, and vapor deposition. When using the system  100 , the electron beam focus can be precisely controlled and repeated for quality control purposes, welds can be repeated on the same machine over a period of time, and electron beam parameters can be transferred between different machines. 
     The system  100  includes structural components that provide a diagnostic system for high power beams. The diagnostic system  100  involves interconnected components or systems including an electron beam gun system generally indicated by the reference numeral  101 , a modified Faraday cup (MFC) system generally indicated by the reference numeral  102 , a positioning system generally indicated by the reference numeral  103 , and a control and data acquisition system generally indicated by the reference numeral  104 . The components are contained in a vacuum chamber  112 . 
     The electron beam is indicated at  111 . The beam  111  is moved via deflection coils  110  and this movement is generally indicated at  111 A. In operation the beam  111  is swept across the slits in the modified Faraday cup system  102 . The beam  111  is swept around the modified Faraday cup system  102  in a circular pattern to enter slits in the modified Faraday cup system  102 . 
     The electron beam gun system  101  can be used for welding and processing. The electron beam gun system  101  basically comprises a filament  105 , cathode  106 , anode  107 , alignment coil  108 , a magnetic lens  109 , and deflection coils  110 . The filament  105  may be of any desired cathode configuration, such as a ribbon type. 
     The modified Faraday cup assembly  102  is mounted on the rotatable/movable MFC assembly  103 . The positioning stage  103  utilizes a rotatable/movable member or stage system to position the modified Faraday cup (MFC) system  102 . The positioning stage  103  includes X, Y and Z translation stages, providing capability of movement in the X, Y, and Z directions as indicated by the double arrows. The positioning stage  103  also includes a rotational stage to provide the capability of rotational movement of the Faraday cup (MFC) system  102 , as indicated by the arrow θ. 
     Mounting the modified Faraday cup system  102  onto the positioning stage  103  allows for controlled, repeated positioning of the modified Faraday cup (MFC) system  102 . In operation, beam waveforms are taken by sweeping the beam  111  around the modified Faraday cup assembly  102 . Additional details and structural elements of the positioning stage  103  are not shown because they are known in the art. 
     The control and data acquisition system  104  functions to control the modified Faraday cup (MFC) system  102  as well as processing and storing the acquired data. Various details and operations of the control and data acquisition system  104  will be described subsequently in connection the operation of the diagnostic system  100 . Basic details and structural elements of the control and data acquisition system  104  are not shown or discussed here because they are systems known in the art. 
     Certain of the elements of the diagnostic system  100  and the procedures for operating the diagnostic system  100  are the same as or similar to the systems shown and described in U.S. Pat. No. 5,382,895, U.S. Pat. No. 5,468,966, U.S. Pat. No. 5,554,926, U.S. Pat. No. 5,583,427, and U.S. Pat. No. 6,300,755. The disclosures of U.S. Pat. No. 5,382,895, U.S. Pat. No. 5,468,966, U.S. Pat. No. 5,554,926 U.S. Pat. No. 5,583,427, and U.S. Pat. No. 6,300,755 are incorporated herein by this reference. 
     Referring now to  FIG. 2 , an illustration shows additional details of the diagnostic system for high powered beams  100  that was previously described and illustrated in  FIG. 1 . As illustrated in  FIG. 2 , the system  100  includes the interconnected components or systems that were described in connection with  FIG. 1  including the modified Faraday cup (MFC) system  102  and the high power beam  111 . The MFC system  102  includes the basic components of: a slit disk assembly  201 , a conducting disk  203  located below the slit disk assembly  201 , a Faraday cup assembly  206  located below the conducting disk  203 , and a start-stop target  214  located proximate the slit disk assembly  201 . A multiplicity of circumferential radial slits  216  and a trigger probe  217  are located in the slit disk assembly  201 . A corresponding multiplicity of circumferential radial slits  212  are located in the conducting disk  203 . In order to keep the system  102  from over-heating during use, a heat sink is placed in close proximity to the components. An active cooling system, using water or other cooling fluid, is integrated into the heat sink as subsequently illustrated. 
     The system  100  provides diagnostics for measuring the power density distribution of the high power and high intensity beam  111 . During operation, the beam  111  is rotated about the central point of the slit disk assembly  201  over the aligned radial slits  216  and  212 . Electrons or ions pass through the aligned radial slits  216  and  212  and are intercepted by the Faraday cup assembly  206  where they are detected and a signal is sent to the measuring and data acquisition system  104  to measure the profile of the beam. Computed tomography can then be used to reconstruct the power density distribution of the beam  111 . 
     In order to prevent damage to the tungsten slit disk assembly  201 , the time over which the beam  111  comes in contact with the tungsten slit disk assembly  201  is reduced. In order to do this, the target block  214  is located to the side of the tungsten slit disk assembly  201 . The target block  214  is made of a refractory metal. The beam  111  is first directed onto the target block  214  as illustrated in  FIG. 2 , and then the beam is translated to the radial slits  216 , where it is translated in a circle indicated at  111 A for a minimum number of rotations and then translated back onto the target block  214 . The trigger probe  217  initiates the system  100 . This is accomplished by trigger probe  217  sensing scattered electrons produced as the beam  111  passes through a region between slits  216  and directly in front of trigger probe  217 . Details of the trigger probe  217  and its operation are described in co-pending U.S. application Ser. No. 60/582,574 filed Jun. 24, 2005 by John W. Elmer, Todd A. Palmer, and Alan T. Teruya titled, “A Trigger Probe for Determining the Orientation or the Power Distribution of an Electron Beam.” U.S. application Ser. No. 60/582,754 filed Jun. 24, 2004 by John W. Elmer, Todd A. Palmer, and Alan T. Teruya titled, “A Trigger Probe for Determining the Orientation or the Power Distribution of an Electron Beam” is incorporated herein by this reference. 
     The diagnostic system  100  provides a system for rapidly measuring the power density distribution of an electron or an ion beam. The system captures beam profiles in a fraction of a second as the beam is moved in a circular pattern over the MFC system  102 . The individual beam profiles are then reconstructed using a computed tomographic method to render an image of the beam shape, size, and power density distribution. The data is gathered and displayed within seconds, enabling near real time adjustments to be made to correct beam problems, such as focusing irregularities, beam astigmatism, and other effects leading to non-symmetric or non-optimum beams. In addition to correcting beam problems, the diagnostic device provides a permanent record of the beam for quality control purposes, a device to repeat the same beam quality on the same machine over a period of time, and a device to transfer beam quality characteristics to multiple machines. 
     Referring again to  FIG. 2 , the diagnostic system for high powered beams  100  will be described in greater detail. The modified Faraday cup (MFC) system  102  includes the following structural components: slit disk assembly  201 , space  202  between the slit disk assembly and conducting disk, conducting disk  203 , space  204  between the conducting disk and the Faraday cup assembly, spacer ring  205 , Faraday cup assembly  206 , space  207  between the Faraday cup assembly and the bottom plate, spacer ring  207 , bottom plate  209 , heat sink  210 , hole  211  in the conducting disk, circumferential radial slits  212  in the conducting disk, hole  213  in the slit disk assembly, start-stop target  214 , mounting ring  215 , circumferential radial slits  216  in the slit disk assembly, and trigger probe  217 . 
     The slit disk assembly  201  of the MFC system  102  is made of an electrically conductive refractory material. Refractory materials are required to minimize damage to the slit disk assembly  201  by the high power beam  111 . This material should also have a high average atomic number to intercept the beam  111 , and be sufficiently thick to prevent the beam  111  from penetrating through to the underlying layers. In the embodiment shown in  FIG. 2 , the slit disk assembly  201  is made of tungsten. 
     The system  100  provides diagnostics for measuring the power density distribution of the high power and high intensity beam  111 . During operation, the beam  111  is rotated about the central point of the slit disk assembly  201  over the aligned radial slits  216  and  212 . Electrons or ions pass through the aligned radial slits  216  and  212  and are intercepted by the Faraday cup assembly  206  where they are detected and a signal is sent to the measuring and data acquisition system  104  to measure the profile of the beam. Computed tomography can then be used to reconstruct the power density distribution of the beam  111 . 
     The diagnostic system  100  provides a system for rapidly measuring the power density distribution of an electron or an ion beam. The system captures beam profiles in a fraction of a second as the beam is moved in a circular pattern over the MFC system  102 . The individual beam profiles are then reconstructed using a computed tomographic method to render an image of the beam shape, size, and power density distribution. The data is gathered and displayed within seconds, enabling near real time adjustments to be made to correct beam problems, such as focusing irregularities, beam astigmatism, and other effects leading to non-symmetric or non-optimum beams. In addition to correcting beam problems, the diagnostic device provides a permanent record of the beam for quality control purposes, a device to repeat the same beam quality on the same machine over a period of time, and a device to transfer beam quality characteristics to multiple machines. 
     In order to prevent damage to the tungsten slit disk assembly  201 , the time over which the beam  111  comes in contact with the tungsten slit disk assembly  201  is reduced. In order to do this, the target block  214  is located to the side of the tungsten slit disk assembly  201 . The target block  214  is made of a refractory metal. The beam  111  is first directed onto the target block  214  and then translated to the radial slits  216 , where it is translated in a circle for a minimum number of rotations and then translated back onto the target block  214 . The trigger probe  217  acts as a trigger to initiate the control and data acquisition system  104  and control the number of rotations of the beam  111  and the translation of the beam  111  back onto the target block  214 . 
     The slit disk assembly  201  is a seventeen (17) slit tungsten disk. The beam  111  is rotated over this disk  201  in a circle. It is important that the beam does not go through two slits at the same time, so the largest diameter beam that is measured corresponds to the spacing between the slits  216 . Keeping the same radial pattern with 17 slits, the size of the beam  111  that can be measured scales directly with the beam rotation diameter. Therefore, for the tungsten disk  201  to be large enough to accommodate a 2 inch diameter beam path, it would allow beams with twice the diameter of the existing design to be inspected, i.e., 0.36 inch diameter beams, etc. The large diameter tungsten disk  201  is capable of measuring beams up to 0.75 inch in diameter. Note that most electron beams, even high power beams, are less than 1 mm in diameter when they are sharply focused. However, defocused beams are often used, particularly for melting and vapor deposition applications, where the beam diameters may be much larger. 
     Referring now to  FIG. 3 , the modified Faraday cup (MFC) system  102  will be described in greater detail. The MFC system  102  includes the slit disk assembly  201  with circumferential radial slits  216  and trigger probe  217 . In order to prevent damage to the tungsten slit disk assembly  201 , the time over which the beam  111  comes in contact with the tungsten slit disk assembly  201  is reduced. The beam  111  is first directed onto the target block  214 . Next the beam  111  is translated to the slit disk assembly  201 . In order to prevent damage to the slit disk assembly  201 , the beam  111  needs to be rotated in a circle over the slit disk assembly  102  for a minimum number of rotations. The beam enters the trigger probe  217  which initiates the control and data acquisition system  104  and controls the number of rotations of the beam  111  over the slit disk assembly  102 . After predetermined number of rotations, the beam  111  is translated back onto the target block  214 . This is accomplished by trigger probe  217  sensing scattered electrons produced as the beam  111  passes through a region between slits  216  and directly in front of trigger probe  217 . 
     As the beam  111  rotates it enters the circumferential radial slits  216  and the diagnostic system produces individual beam profiles using a computed tomographic method to render an image of the beam shape, size, and power density distribution. The data is gathered and displayed within seconds, enabling near real time adjustments to be made to correct beam problems, such as focusing irregularities, beam astigmatism, and other effects leading to non-symmetric or non-optimum beams. In addition to correcting beam problems, the diagnostic device provides a permanent record of the beam for quality control purposes, a device to repeat the same beam quality on the same machine over a period of time, and a device to transfer beam quality characteristics to multiple machines. 
     Referring now to  FIG. 4 , another embodiment of a diagnostic system for high powered beams is illustrated. The diagnostic system for high powered beams includes the interconnected components or systems that were described in connection with  FIG. 1 , including the modified Faraday cup (MFC) system  102  and the high power beam  111 . The modified Faraday cup (MFC) system  102  includes the following structural components: slit disk assembly  401 , space  402  between the slit disk assembly and conducting disk, conducting disk  403 , space  404  between the conducting disk and the Faraday cup assembly, spacer ring  405 , Faraday cup assembly  406 , space  407  between the Faraday cup assembly and the bottom plate, spacer ring  407 , bottom plate  409 , heat sink  410 , hole  411  in the conducting disk, circumferential radial slits  412  in the conducting disk, hole  413  in the slit disk assembly, start-stop target  414 , mounting ring  415 , circumferential radial slits  416  in the slit disk assembly, holes in the heat sink  410 , fluid in  418 , and fluid out  419 . 
     The diagnostic system for high powered beams provides diagnostics for measuring the power density distribution of the high power and high intensity beam  111 . During operation, the beam  111  is rotated about the central point of the slit disk assembly  401  over the aligned radial slits  416  and  412 . One of the slits  416  acts to initiate the system  100 . Electrons or ions pass through the aligned radial slits  416  and  412  and are intercepted by the Faraday cup assembly  406  where they are detected and a signal is sent to the measuring and data acquisition system  104  to measure the profile of the beam. Computed tomography can then be used to reconstruct the power density distribution of the beam  111 . 
     The diagnostic system  100  provides a system for rapidly measuring the power density distribution of an electron or an ion beam. The system captures beam profiles in a fraction of a second as the beam is moved in a circular pattern over the MFC system  102 . The individual beam profiles are then reconstructed using a computed tomographic method to render an image of the beam shape, size, and power density distribution. The data is gathered and displayed within seconds, enabling near real time adjustments to be made to correct beam problems, such as focusing irregularities, beam astigmatism, and other effects leading to non-symmetric or non-optimum beams. In addition to correcting beam problems, the diagnostic device provides a permanent record of the beam for quality control purposes, a device to repeat the same beam quality on the same machine over a period of time, and a device to transfer beam quality characteristics to multiple machines. 
     In order to prevent damage to the tungsten slit disk assembly  401 , the time over which the beam  111  comes in contact with the tungsten slit disk assembly  401  is reduced. In order to do this, the target block  414  is located to the side of the tungsten slit disk assembly  401 . The target block  414  is made of a refractory metal. The beam  111  is first directed onto the target block  414  and then translated to the radial slits  416 , where it is translated in a circle for a minimum number of rotations and then translated back onto the target block  414 . The copper heat sink  410  is located adjacent the slit disk assembly  401 , the conducting disk  403  located below the slit disk assembly  401 , the Faraday cup assembly  406  located below the conducting disk  403 , and the start-stop target  414 . The copper heat sink  410  includes cooling tubes  417  that allow fluid to be circulated in a spiral pattern around system for cooling. The fluid is introduced to the cooling tubes  417  as illustrated by the arrow  418  and the fluid exits as illustrated by the arrow  419 . In the embodiment shown in  FIG. 4  the fluid is water. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.