Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
  • H01J41/12—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B17/00—Insulators or insulating bodies characterised by their form
  • H01B17/26—Lead-in insulators; Lead-through insulators

Definitions

• This invention is directed to a high voltage feedthrough particularly useful for ion pumps.
• the ion pump is basically a low pressure cold cathode Penning discharge.
• the electric fields trap electrons in a potential well between two cathodes, and the axial magnetic field forces the electrons into circular orbits to prevent their reaching the anode. This combination of electric and magnetic fields causes the electrons to travel long distances in oscillating spiral paths before colliding with the anode.
• the sputtered material having a neutral charge, travels in a straight line from the point of sputtering.
• the high voltage feedthrough feeding the anode includes a ceramic insulator which is exposed to the interior of the pump.- In the conventional pump, sputtered material deposits on the ceramic insulator. After a sufficient time has elapsed, a conducting laver of cathode metal builds up. This layer short-circuits the anode to the main body of the pump which is at cathode potential. Because sputtering is directly proportional to the anode current, the life of the pump is directly proportional to the total charge which has flowed through the anode circuit.
• An ion pump according to the invention includes a pump vacuum body having a pumping chamber containing an anode and a cathode.
• a feedthrough arrangement including a tubular insulator extends into an opening in the vacuum body to afford electrical connection to the
• the feedthrough insulator is configured to be out of the line-of-sight of ion pump sputtering so that it avoids sputter-generated deposition.
• FIG. 1 is a side-elevational view of an ion 20 pump which contains a first preferred embodiment of the high voltage feedthrough in accordance with this invention.
• FIG. 2 is an enlarged sectional view, taken generally along the line 2-2 of FIG. 1; and 25 FIG. 3 is a further enlarged view, similar to
• FIGURE 2 showing a second preferred embodiment of the high voltage feedthrough in accordance with this inven ⁇ tion.
• Ion pump 10 may be a 0.2 liter per second ion pump, which is a convenient and common size. When a higher pumping rate is desired, it is usual t ⁇ connect a plurality of such ion pumps in parallel.
• Ion pump 10 has a cylindrical tubular vacuum body 12 which is at cathode potential.
• the body 12 has connected thereto a suction tube 14 which is connected to the vacuum space from which ion pump 10 is to pump gases.
• the cylin ⁇ drical tubular nature of body 12 is seen in FIG. 2, where the ends of the body are closed by caps 16 and 18. Interiorly of and held by the caps 16 and 18 against shoulders in the body 12 are cathode discs 20 an 22. These discs are commonly of titanium.
• U-shaped permanent magnet 24 has its pole faces 26 and 28 positioned outside of the caps 16 and 18 in order to provide a magnetic field in the left and right direction in FIG. 2 and normal to the sheet in FIG. 1.
• one or more individual.magnets provided with suitable pole pieces could be used.
• Anode 30 is a metallic right circular cylindrical tube of thin wall construction. It is mounted centrally of body 12 and equally spaced from cathode discs 20 and 22. It is held in this position by means of post 32 which is secured to anode 30 and extends radially outwardly therefrom into a feedthrough 33. Post 32 defines a feedthrough axis which is normal to the axis of the anode 30 and the pump vacuum body 12. Recess 34 is formed in a portion of the outer surface of the pump body 12. Within recess 34 is opening 36 by which the recess 34 opens into the interior of the pump body 12. Cup 38 is mounted within recess 34.
• Cup 38 is basically a reducer, having a larger diameter portion within the recess 34 and a smaller diameter portion retaining an upper boss 40 of ceramic insulator 42.
• the insulator 42 has a cylindrical hole therethrough, and within the lower end of the hole there is mounted a cup 44.
• the cup 44 has a hole therein, and the post 32 extends through the hole in the cup 44.
• a shoulder on the post 32 positions the post 32 with respect to the cup 44.
• Cups 38 and 44 are metallic, as is post 32.
• the cups 38 and 42 are brazed to the ceramic insulator 44, and the outer cup 38 is braced to body 12.
• the inner cup 44 is brazed to the post 32. In that way, a vacuum seal with electrical insulation is provided.
• a fitting 46 is provided with an interior opening and external threads.
• the fitting 46 is brazed onto outer cup 38. With the opening in the fitting 46, the pin 32 is accessible.
• a conductor (not shown) may be secured onto the threads of the fitting 46 and has a socket adapted to receive post 32.
• the fitting 46 and the body 12 are at cathode potential, while the socket is at anode potential to provide the requisite voltage between the anode 30 and the cathode discs 20 and 22. Suitable dimensions are disclosed in the Wolfgang Knauer article, cited above, the entire disclosure of which is incor ⁇ porated herein by this reference.
• the magnetic field is usually above 1200 Gauss, while the applied voltage may be about 3.5 kilovolts.
• the exterior of the insulator 42 is provided with a radially outwardly projecting annular flange, or shoulder, 48 above the opening 36 in the body 12.
• the continuous upper surface 49 of the flange 48 extends all around the insulator 42 and is not visible through opening 36, and in addition, the flange 48 has a greater outer diameter than the opening 36 and, thus, the outer cylindrical surface of flange 48 is not visible through openinq 36.
• FIG. 3 shows in section, with parts broken away, a second preferred embodiment of the feedthrough of this invention, this time shown on ion pump 52.
• Ion pump 52 has the same body 54, caps 56 and 58, cathode discs 60 and 62, and pole pieces 64 and 66 of a permanent magnet, corresponding to the similar parts shown in FIGS.
• anode 68 is coaxial with the body 54 and has a radially extending post 70.
• Post 70 has a shoulder 72 thereon, similarly to post 32.
• Post 70 is used to hold the anode 68 in position and to supply anode potential to it.
• Feedthrough 74 is of more simple construction and has fewer parts than the feedthrough 33 of FIG. 2 by employment of a ceramic insulator as the threaded end of the connection fitting.
• Tubular ceramic insulator 76 is carried on hollow reducing bushing, or cup, 78 which is secured within recess 80 which is radially positioned in the wall of body 54. Opening 82 extends between recess 80 and the interior of the body 54.
• Ceramic insulator 76 has a cylindrical interior wall 84 of the same diameter throughout its entire length and a coaxial cylindrical exterior wall 86 which is interrupted by threads 88 and radially outwardly projecting annular flange 90.
• Flange 90 is of equal or preferably larger diameter than opening 82.
• Cup 78 engages upon the exterior wall 86 above flange 90 to secure the insulator 76 in place, with its axis coextensive with the axis of radial post 70.
• Cup 92 is secured against shoulder 72 and is secured against the interior wall 84 at its lower end, as shown in FIG. 3. All joints are brazed so that the exterior of the insulator 76 is sealed to the body 54 and the interior of the insulator 76 is sealed to the post 70.
• connection to the anode 68 can be made by placing a socket over the post 70.
• the socket can be held in place by means of engagement on the threads 88.
• a separate cathode connection must be made.
• the cathode potential is usually the potential of the equipment to which the ion pump is attached and, therefore, the cathode connection is easily made.
• annular flange 90 Since the diameter of annular flange 90 is greater than the opening 82, neither the outer surface 94 or the top surface 96 of the annular flange 90 can be seen 1 throuqh the opening 82. Neither can the portion 98 of the insulator 76 above flange 90 and below cup 78 be seen through opening 82. Each of these surfaces extends completely around the insulator 76. Therefore, when 5 sputtering occurs on the titanium cathode surfaces and neutral metal particles are sputtered away, the particles cannot reach the outer surface 94 of annular flange 90 and the insulator surfaces 96 and 98 above it. There ⁇ fore, the insulator cannot be shortcircuited by the

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• 1985
  • 1985-12-19 US US06/810,486 patent/US4687417A/en not_active Expired - Lifetime
• 1986
  • 1986-10-01 EP EP87900355A patent/EP0252113B1/en not_active Expired
  • 1986-10-01 JP JP62500598A patent/JPS63502386A/ja active Granted
  • 1986-10-01 WO PCT/US1986/001856 patent/WO1987004005A1/en active IP Right Grant
  • 1986-10-01 DE DE8787900355T patent/DE3670400D1/de not_active Expired - Fee Related

Patent Citations (2)

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