Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J7/00—Details not provided for in the preceding groups and common to two or more basic types of discharge tubes or lamps
  • H01J7/14—Means for obtaining or maintaining the desired pressure within the vessel
  • H01J7/18—Means for absorbing or adsorbing gas, e.g. by gettering
  • H01J7/183—Composition or manufacture of getters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J7/00—Details not provided for in the preceding groups and common to two or more basic types of discharge tubes or lamps
  • H01J7/14—Means for obtaining or maintaining the desired pressure within the vessel
  • H01J7/18—Means for absorbing or adsorbing gas, e.g. by gettering
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
  • H05H7/14—Vacuum chambers

Definitions

• Non-evaporable getter pumping device and method for implementing this getter are described in detail below.
• the present invention relates to improvements made to pumping by a non-evaporable getter (NEG) to create a very high vacuum in an enclosure defined by a metal wall capable of releasing gas on its surface.
• NEG non-evaporable getter
• the metal walls of the vacuum enclosure constitute an inexhaustible source of gas.
• the hydrogen contained in the construction metal diffuses freely in the thickness of the metal and is released to the surface defining the enclosure.
• the vacuum level obtained in one enclosure is therefore defined by the dynamic balance between the degassing at the surface defining the enclosure and the pumping speed of the pumps used. Obtaining a high vacuum implies both great cleanliness of the surface of the enclosure reducing the emission of gas and a high pumping speed. For vacuum systems of particle accelerators whose chambers are generally of small section, the pumps must be brought close to each other or else a continuous pumping must be implemented, in order to overcome the limitation of conductance.
• this material is capable of producing chemically stable compounds by reaction with the gases present in a vacuum enclosure (in particular H 2 , 0 2 , CO, C0 2 , N 2 ) and this reaction gives rise to the disappearance of the molecular species concerned, which corresponds to a pumping effect.
• the surface of the getter must be clean, that is to say free from any passivation layer formed during the exposure of the getter to ambient air.
• This passivation layer can in particular be eliminated by diffusing the surface gases (mainly O 2 ) inside the getter by heating (activation process of the getter which is then called non-evaporable getter: NEG).
• the non-evaporable getters have the advantage of being able to be produced in the form of a ribbon which can then be put in place all along the vacuum enclosure so that a distributed pumping effect results therefrom.
• the level of vacuum that can be obtained in the enclosure remains defined by the dynamic balance between the pumping speed (whatever the means used) and the degassing speed of the metallic surface of the enclosure (whatever the cause)? in other words for a given pumping speed, the vacuum level remains dependent on the degassing rate in the enclosure.
• the object of the invention is therefore to propose an improved solution which makes it possible to solve this problem and which, because of the degassing rate occurring in the enclosure, significantly increases the efficiency of the pumping means used and leads to a improvement of several orders of magnitude of the vacuum level likely to be created in the enclosure.
• a getter layer according to the invention does not occupy any sensitive space, and offers the advantage of providing a pumping effect under zero bulk, which allows its implementation even in cases where the geometric constraints would prohibit the use of a getter in the form of a ribbon.
• the design of the vacuum chamber could be greatly simplified by eliminating the lateral pumping channel which has become unnecessary.
• the material used has certain characteristics isolated or combined in whole or in part.
• the material must of course have a high adsorption capacity for the chemically reactive gases present in the enclosure despite the barrier effect provided by the thin layer.
• the material must also have great power absorption and high diffusivity for hydrogen, with the capacity to form a hydride phase. It must, moreover, have a dissociation pressure of the hydride phase of less than 10 ⁇ 13 Torr at approximately 20 ° C.
• the material must also have an activation temperature as low as possible, compatible with the drying temperatures of the vacuum systems (approximately 400 ° C for stainless steel chambers, 200-250 ⁇ C for copper and aluminum alloy chambers) and compatible with the stability of the material in air, at approximately 20 ° C; in these conditions, in general the activation temperature must be at most equal to 400 ° C.
• the material must have a high solubility, greater than 2%, for oxygen in order to allow the absorption of the quantity of oxygen pumped to the surface during a large number of activation and exposure cycles. to the air.
• a high solubility greater than 2%
• oxygen concentration of 2% in the getter would be reached after approximately 10 cycles, without count the other gases pumped during the vacuum operation; thicker layers could be considered, but they would take longer to deposit and their adhesion could become less good.
• titanium and / or zirconium and / or hafnium and / or vanadium and scandium which have a solubility limit, for oxygen, at ambient temperature, greater than 2% can constitute getter suitable for constituting a thin layer coating within the scope of the invention.
• titanium, zirconium and hafnium have a solubility for oxygen close to 20%
• vanadium and scandium have a high diffusivity for gases. It is of course also possible to retain, alone or in combination with at least one of the aforementioned bodies, any alloy comprising at least one of the bodies, so as to combine the effects obtained, or even to obtain new effects not directly resulting from the accumulation of individual effects.
• titanium can be activated at 400 ° C, zirconium at 300 ° C and the alloy Ti 50% - Zr 50% at 250 ° C. Activation at these temperatures for two hours reduces the desorption rate induced by electron bombardment with an energy of 500 eV by four orders of magnitude and produces pumping speeds for CO and C0 2 of the order of 1 ls "1 per cm 2 of surface. It should be added as an additional advantage that the implementation of a getter in the form of a thin layer adhering to a metal substrate makes it play the role of thermal stabilizer capable of limiting the temperature. ⁇ ture in the thin layer.
• This arrangement is very advantageous because it makes it possible to use, as a getter, materials with high pyrophoricity without any safety problems being posed because of the stabilizing effect conferred by the substrate with a high thermal capacity compared to the heat of combustion of the thin getter layer.
• thermodynamically unstable materials which widens the field of choice of the optimum material as a getter. This possibility can be exploited in a simple manner by implementing a technique of simultaneous cathodic pulverization of several bodies, using a composite cathode which is discussed below.
• the invention provides a method for implementing a non-evaporable getter in order to create a very high vacuum in an enclosure defined by a metal wall capable of releasing gas on its surface, which method includes the following steps: a) the enclosure is cleaned; the thin layer deposition device is introduced inside the enclosure; a relative vacuum is created in the enclosure; we perform a steaming the enclosure to remove as much of the water vapor as possible; then the getter is deposited in a thin layer on at least most of the surface of the wall defining the enclosure; b) the atmospheric pressure in the enclosure is restored; and the depositing device is extracted from the enclosure; c) the enclosure coated internally with the thin getter layer is assembled within the installation which it is to equip; we create a relative vacuum; steaming the installation at the desired temperature while maintaining the enclosure at a temperature below the activation temperature of the getter; d) stopping the steaming of the installation and simultaneously raising the temperature of the enclosure to the activation temperature of the getter which is maintained for a predetermined period (
• the surface of the getter thin layer is clean and its thermal degassing or induced by bombardment of particles (ions, electrons, or synchrotron light) is greatly reduced.
• a molecular pumping phenomenon appears due to the chemical reaction, on the surface of the getter layer, of the gases present in the enclosure.
• a vacuum evaporation process To deposit the getter in a thin layer on the surface of the wall of the enclosure, it is certainly possible to use a vacuum evaporation process; However, such a process seems difficult to control effectively in order to constitute a uniform and homogeneous layer, in particular during the simultaneous deposition of several bodies, and it seems in practice more advantageous to have recourse to a sputtering process which allows much control. effective conditions for the formation of the thin layer.
• a sputtering process makes it possible to deposit several materials simultaneously to form an alloy type getter combining materials having different optimal characteristics, the accumulation of which is sought, as indicated above.
• a cathode is formed, intended to be placed centrally in the enclosure, which can be constituted by a twist of several (for example two or three) metallic wires of the respective materials of the alloy which are wish to train.
• the use of a composite cathode thus constituted allows the simultaneous deposition of several metals and therefore artificially create an alloy of thermodynamically unstable materials which it would not be possible to obtain by other traditional routes.
• the means proposed by the invention offer the unequaled possibility of producing high voids from 10 "10 to 10 ⁇ 14 Torr for laboratory applications, for thermal and / or phonic insulation and for surface analysis systems, especially when they are used for reactive materials.
• the implementation of the invention in vacuum systems often exposed to the atmosphere or operating under low vacuum levels would very quickly lead to saturation of the surface of the getter in a thin layer and that the advantages mentioned above could not be achieved.
• a particularly interesting field of application of the invention consists in obtaining and maintaining over a long period of time a high vacuum in the accelerators / accumulators of particles whose conditioning period by circula ⁇ tion of the particle beam would then be erased and in which the problems of vacuum instability would be eliminated.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Compressors, Vaccum Pumps And Other Relevant Systems (AREA)
• Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
• Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
• Fats And Perfumes (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
• Physical Vapour Deposition (AREA)
• Finger-Pressure Massage (AREA)
• Thermal Insulation (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

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• 1996
  • 1996-06-19 FR FR9607625A patent/FR2750248B1/fr not_active Expired - Lifetime
• 1997
  • 1997-06-18 AT AT97929213T patent/ATE233946T1/de active
  • 1997-06-18 PT PT97929213T patent/PT906635E/pt unknown
  • 1997-06-18 CA CA2258118A patent/CA2258118C/fr not_active Expired - Lifetime
  • 1997-06-18 AU AU33404/97A patent/AU3340497A/en not_active Abandoned
  • 1997-06-18 ES ES97929213T patent/ES2193382T3/es not_active Expired - Lifetime
  • 1997-06-18 DK DK97929213T patent/DK0906635T3/da active
  • 1997-06-18 US US09/202,668 patent/US6468043B1/en not_active Expired - Lifetime
  • 1997-06-18 EP EP97929213A patent/EP0906635B1/de not_active Expired - Lifetime
  • 1997-06-18 JP JP50227698A patent/JP4620187B2/ja not_active Expired - Lifetime
  • 1997-06-18 WO PCT/EP1997/003180 patent/WO1997049109A1/fr not_active Ceased
  • 1997-06-18 RU RU99100321/09A patent/RU2193254C2/ru active
  • 1997-06-18 DE DE69719507T patent/DE69719507T2/de not_active Expired - Lifetime
• 1998
  • 1998-12-17 NO NO19985927A patent/NO317454B1/no not_active IP Right Cessation

Non-Patent Citations (1)

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