FR2515869A1 - ELECTRONIC TUBE AND CATHODE WITH HIGH EMISSION IMPREGNATION - Google Patents

Abstract

THE INVENTION CONCERNS THERMO-ELECTRONIC CATHODES. AN IMPREGNATED CATHODE ESSENTIALLY CONSISTS OF A 10, 12 METAL PARTICLE MATRIX CONSISTING OF TUNGSTENE OR MOLYBDENE, WHICH IS IMPREGNATED WITH AN ALKALINE-EARTH METAL ALUMINATE CONTAINING AT LEAST BARIUM OXIDE AND ONE METAL OXIDE CONSISTING OF IRIDIUM AND RHENIUM OXIDES, MIXTURES IN THE FORM OF POWDER AND MELT TOGETHER TO FORM AN INTER-OXIDE COMPOUND 20 EMPLOYING THE INTERSTICES OF THE MATRIX. THIS STRUCTURE PROVIDES A VERY HIGHER EMISSION CURRENT DENSITY THAN CONVENTIONAL TUNGSTEN CATHODES, WITH A LONG LIFETIME. APPLICATION TO HYPERFREQUENCY ELECTRONIC TUBES.

Description

the present invention relates to electron tubes

  thermoelectronic emission, and especially those

  They are used for microwave applications and in particular M and B type impregnation cathodes for such tubes.

  The thermoelectric emission density and the dura-

  of the heated cathodes of such tubes constituted

  general limitation factors in performance

  these and the expected lifetime It can be calculated that the

  available output of a tube proportionally increases

  to the fifth power of the cathode emission density, assuming that the emission density is the limiting factor, so that a cathode capable of operating at a high emission density would

  to design electron guns and electron optics

  with lower beam convergence ratios,

  and would lead to better performance A requirement

  additional, especially in cannons equipped with grill-

  the, consists in that the cathode must be capable of furnishing

  It is important to know that high emission densities at lower temperatures than those normally associated with conventional tungsten matrix impregnated cathodes, ie type B and M cathodes, are known. vapor phase, on the surface of type X cathodes special metal coatings such as metal coatings

  osmium or iridium Such coatings reduce the energy

  and improve the emission, but they are cost-

  both in terms of the materials themselves and the

  spray application In addition to the additional cost

  shut down the spraying operation to apply the

  clothing, the duration during which the issue is actually

  improved temperature is limited to temperatures above 107500, which in turn limits the service life of the

tube.

  It is also known to incorporate these special metals.

  ciales, especially iridium, in the matrix itself,

  for example by mixing a certain percentage of irides-

  god: in the form of particles with tungsten particles

  In particular, although this is very satisfactory, the optimum amount of iridium in the form of particles or other special metal of is added to the matrix strongly increases the co-ft of the cathode because the metals in the form of particles

are expensive.

  There is therefore a need for a cathode

  high emission type, impregnation type, and a

  Thermoelectronic emission tube which eliminates the incon-

  and the above limitations.

  The general object of the invention is to provide a

  advanced high-emission cathode of the impregnated type

  tion, and an electron tube, which have a longer

  of living than the cathodes of the prior art, without having the colt resulting from the use of a matrix comprising a

special metal improvement.

  Another object of the invention is to produce a cathode and an electron tube having the characteristics

  above, which provide the improved performance of a

  M-type impregnation thode and a corresponding tube, using iridium or other emission enhancing material, in a more economical form, and

  to use the manufacturing and conventional techniques

  for the production of conventional impregnated cathodes

  The invention also aims to provide a cathode and an electron tube having the above characteristics, in which the need for special coatings

  deleted and the need to incorporate the subject matter of

  metal particles in the matrix.

  this in significant quantities is also removed.

  The object of the invention is also to provide a cathode and an electron tube having the above characteristics which provide an increased emission density to

  temperatures lower than conventional tungsten cathodes

  stene impregnated, and which additionally provide a density of

  high voltage to design optical and electronic guns with lower beam convergence ratios. It is another object of the invention to provide a high emission impregnation cathode having a uniform emission during its useful life and the duration of which

of life be significantly increased.

  The invention is based on the discovery of the fact

  that it is not obligatory that the metal that provides the

  emission, such as, for example, iridium, in the abovementioned patent application, or employed in metallic form, in accordance with past practice.

  incorporate smaller amounts of this material of

  improvement of the emission in the impregnation material

  same, preferably in the form of its oxide In a

  of the invention, there is a thorough mixing of

  of the oxide of the emission-enhancing metal, in the form of a powder, with a powder of an alkaline earth metal aluminate, and the mixture is heated to form an interoxide compound. the cathode of a

  classical way, for example by bringing to its point of

  the impregnating material of the interoxide type, and permitting it to impregnate a matrix, for example made of tungsten or molybdenum. The impregnation procedure is practically the same as that which is known in the current manufacture of

  impregnation cathodes Because the improvement component

  emission is already part of the impregnating

  In this way, a homogeneous source is available for migration to the emitting surface, thus obtaining a long service life, a good stability and an increased emission. The invention will be better understood on reading the

  description that follows of an embodiment and in

  Referring to the accompanying drawings in which: Figure 1 is a schematic representation of

  components of the cathode of the invention, its mode of

brication and its assembly.

  Figure 2 is an enlarged section of an element

  emission of a finished cathode, once the impregnated

  has been completed and that this element is ready for use

  tion. Figure 3 is a section of a fully assembled button-type cathode comprising a heating element constructed in accordance with the invention. Figure 4 is a sectional view of a klystron having a thermoelectronic cathode constructed in accordance with the invention.

  Figure 5 is a comparative graph of a catheter

  classic and a cathode constructed in accordance with

  vention. We will now consider Figure 1 which is a greatly enlarged schematic representation of the elements

  components of the cathode constructed in accordance with

  The aluminate and the matrix that the aluminate impregnates into the matrix comprise particles of tungsten or molybdenum or other suitable refractory metal. If the cost is not considered, then could use metals such as iridium and analogous metals as

  that matter of the matrix It is also possible to con-

  tremble the matrix in the form of a mixture of particles,

  as a mixture of tungsten and molybdenum, indicated in 12.

  The metal particles preferably have a size of 2 to

  8 pm, and if more than one metal is used, the

  in an operation 14 to form a dispersion

  Then they are compressed and subjected to frying

  enough space to obtain agglomeration and to form

  a self-supporting matrix structure This definite structure

  a set of interstices or pores throughout the matrix.

  this metallic which are connected to each other throughout the

  body of the matrix, so that there may be migra-

  The impregnating material is applied to the electron-emitting surface, as will be described later. The particles of the matrix are typically subjected to pressures of 3500 bar while at a temperature

  sintering process suitable for producing an agglomeration in

  Once the matrix has been formed, the electron-emitting surface is fabricated by

classic, to make it flat.

  The impregnating material consists of

  known substances for impregnating cathodes, to which

  a metal selected from the group consisting of iridescence

  dium and rhenium, preferably in the form of one of

  its oxides. These materials are combined in the form of a

  dre and mixed into a uniform dispersion

  The constituents of the impregnating material are

  preferably the following: barium carbonate, aluminum oxide

  calcium carbonate, and a metal (oxide) for

  emission, chosen from among the materials listed below.

  above As will be considered, the quantities of these materials are chosen so that they correspond to quantities

  stoichiometric, so that the subsequent heating

  an inter-oxide compound which is thought to have a structural

  Uniform and Specific Chemistry The mixture is heated in operation 19 at a temperature above its point of

  such as 11000 C, for a sufficient period of time

  te to achieve a complete decarbonization of the mixture, and

  to form the interoxide compound 20 which may be

  Ba O Al 200 Ca O MO.

  The exact chemical formula resulting from the heating of this mixture to form an inter-oxide compound is not known. However, it is considered that physical indices suggest that it is a eutectic and that a formula of the type general given above characterizes a representative form of the resulting material It is not clear the physical and chemical properties of this material, especially when incorporated in the matrix However, it is found that the resulting cathode provides a greatly improved emission , while requiring a small amount of metal enhancement component In addition, this improvement is achieved by chemical incorporation

  and physics of the metal of improvement, in a form of

  oxide, in the impregnating material, being placed in the interstices of the cathode itself instead of being in metallic form, either as a surface coating its Lt as

  than the metallic constituent of the matrix, in the form of

  As it is known in the prior art As a result of this, the cathode of the invention functions without showing any loss of its essential improvement metal by spraying from a surface coating placed on the emitting surface. , for example under the effect of a bombardment by positive ions It is also not necessary

  to use the emission enhancement metal in the

  trice itself, which imposes the use of diffusion processes in the impregnation material, as well as a more

  large amount of the emission enhancement material.

  Once the impregnating material has been formed,

  the alkaline earth metal aluminate compound is melted

  The reaction is carried out by the reaction of the metal and the interoxide, and is poured to fill the pores of the matrix. After cooling, the excess aluminate is mechanically removed from the emitting surface to leave a cathode of the same type.

  finished button having a structure which is practically

  2 in which the emitting surfaces are designated 22a. The cathode button element is now ready for mounting in a

  electronic tube device such as a klystron.

  We will now consider more particularly

  FIG. 3, which shows a section of the cathode

  completed tone, which is suitable for the above purpose The metal matrix 22 is contained in a cylindrical housing 24 in

  tungsten or molybdenum containing a transverse plate

  the 26 acting as a floor to support the cathode.

  The latter is heated indirectly by an element

  two-wire heater 28, such as a tungsten wire, which heats

  The heating element 28 may be self-supporting and mounted on branches 29, as shown, or it may be provided with an alumina insulation (not shown) and may be Inside the housing 24 The plate 26 protects the heating element 28 against the active material The matrix 22 can be introduced directly to the press inside the housing 24, or it

  can be manufactured as before, by carrying out the operation

  impregnation ration after mounting the matrix in the

  Before giving specific examples of manufacturers

  cation of the cathode, will be described hereinafter the use of this cathode in an internal structure of an amplifier

to klystron.

  We will therefore consider the figure

  4 which shows schematically the klys- amplifier

  tron constructed in accordance with the invention and employing the cathode described herein A thermoelectronic cathode transmitter

  22, constructed in accordance with FIGS. 1 to 3, is thus sup-

  carried by a base 24 mounted in an insulating sleeve 30.

  The cathode 22 is heated by radiation from the

  Heating element 28 supported on legs 29, from the lower part 32 of the insulating hermetic envelope 30 An electron beam 34 is extracted from the front surface 22a of the cathode emitter 22 by a voltage, positive by relative to the emitter 22, which is applied to the anode 38 The electron beam 34 converges to a diameter

  b under the effect of the electric field of convergence and it

  pours an opening 40 in the anode 38, from which

  it passes through an interaction tunnel 42 having a diameter a.

  A solenoid magnet 44 establishes an axial magnetic field

  between iron pieces 46, to maintain the

  34 electron beam focused with a cylindrical contour.

  After leaving the magnetic field, the beam 34 becomes

  late under the effect of its own space charge forces

  repellent, and is intercepted by a metal collector

that 48.

  Interaction spaces 50, 51, 52 are distributed at intervals along the slide tube 42 and are formed

  between re-entrant projections 54, 55, 56 of metal cavities

  58, 59, 60, which resonate at frequencies

  The first cavity 58 is energized via a coupled transmission line 62 from a signal source.

  external (not shown) The resonant electric field

  sulting in space 50 produces a speed modulation

  beam 34 When the beam passes through the slide tube

  52, speed modulation produces

  electrons, that is to say a modulation of the current.

  intermediate "floating" 59 is excited by the modula-

  current and in turn produces a modulation of

  the amplified alternating component of the induced current of the wall currents in the output cavity 60, from which amplified microwave energy is extracted.

  via a coupled output waveguide, 64.

  The power that is generated by a tube such as

  the klystron of Figure 4 is obviously limited to a

  their inferior to the continuous power of the beam at

  whose microwave energy is converted into the diameter

  be b of the beam 34 must be smaller than the diameter a of the

  In practice, a characteristic value of

that is b = 2 a / 3.

  the diameter of the sliding tube must be suf-

  weak enough to effectively couple the elec-

  Thus, its maximum diameter is determined by the electron wavelength of the beam, that is to say by the distance that the electrons of the beam.

  beam travels in a radio frequency cycle We can

  by a mathematical analysis of the functioning of a klystron that the available energy increases as the fifth

  power of cathode emission density.

  improvement of the emission density leads to an increase in

  extremely important output power output

  As an example, a two-fold increase in the emission density results in an increase of the output power by a factor of

  32 To accept this increase in output power

  the construction of klystron tubes involves modifications to provide higher acceleration voltage and additional insulation possibilities

  and removal, as well as additional cooling.

  Example (Iridium) The following example illustrates the formulation of the impregnating material comprising an inter-oxide compound and shows test results obtained with this material. Stoichiometric amounts of barium carbonate, calcium carbonate, oxide were mixed together. of iridium and aluminate, in the following proportions: aluminate 6, barium carbonate 1, calcium carbonate 1, iridium oxide 1 After mixing these substances, they were subjected to heating in an oven in the air , between 1100 and 12000 C for 4 hours to

  combine them into an interoxide compound.

  hereinafter referred to for this compound because it is considered to be comparable to a metal alloy, i.e.

  seems to form a eutectic very similar to a metal alloy

  The formula could be written as follows:

  Ba Ca A 1203 Ir O 5, considering the compound from this point of view.

  In any case, when carbon and some of the oxy-

  gene are removed, these oxides combine into a compound

  By analogy, it is not uncommon in the study of ceramic materials, silicates or other

  materials of the glass type, to represent them in the form

  The resultant impregnating material 20, in the form indicated above, can be considered as a quaternary system, which means that the interaction of such a system of oxide-based compounds can be represented.

  in the form of a set of phase diagrams in the-

  what can be shown that proportions of each of the con-

  In some cases, there are some melting points that depend on

quantities involved.

  Figure 5 shows a comparison of density

  emission of a cathode constructed according to the invention

  (dashed line) with a conventional cathode

  be in continuous line) In general, the cathodes present

  an increasing emission density for a rising temperature, within a certain temperature range, beyond which a further increase in temperature does not significantly increase the emission density. In this range, it is considered that the cathode is operating. In a temperature-limited region, and beyond, it is considered that the cathode operates in a space-charge limited region. In practical use of the cathodes, it is desired to operate just above the range. above, to obtain a maximum emission density at the lowest possible temperature the plot of the dashed curve corresponds to the operation of the cathode of the invention

  in this desirable range, just inside the

  in which the emission is limited by the expense of

  As can be seen, for a given operating temperature, for example 10500, an increase in the output emission density corresponding to almost one

  factor of two, compared with a tungsten cathode

conventional type B impregnation.

  By employing the metal enhancement component as a constituent of the impregnating material, substantial savings can be realized in the amount of this material compared to US Pat. No. 800,837.

  above mentioned, in which the matrix constitutes 80% of the

  20% and 20% of the matrix are in iridium, for example, the invention uses iridium in the form of oxide only in the proportion 1/9, for example, of the impregnating material,

  which itself constitutes only about 20% to 25% of the cathode.

  Thus, the performances obtained are comparable to those

  resulting from the use of the metal component of

  in the form of metal in the matrix, while at the same time

  requiring that 15% of the quantity of material, when

according to the invention.

  It goes without saying that many modifications can

  must be made to the device described and shown without

depart from the scope of the invention.

REVEITDICATIONS

  1 improved cathode (22) for use with

  in an electron tube for producing, when heated, an electron beam having a high current density, characterized in that it comprises a

  group of agglomerated metal particles (10, 12) presenting

  between them interstices which are distributed in a

  practically uniform throughout the matrix and-which define-

  in the latter a predetermined initial porosity, this matrix consisting of metal particles (10, 12)

  selected from the group consisting of tungsten and molyb-

  dene or mixtures thereof, this matrix being

  processed to bring the particles into close contact with each other so that the particles are

  together in their contact regions, the particles

  retaining however their discrete character so as to form the interstices between them and to define a volume

  significant vacuum throughout the matrix, and a matter of

  electron-emitting compound that fills the interstices of

  the matrix to form with it a block of

  of negligible porosity, the impregnating material

  emitter comprising an alkali metal aluminate

  lino-terrestrial material, comprising at least barium oxide, and further containing at least one metal oxide (MO 2) selected from the group consisting of iridium and rhenium oxides, said alkaline earth metal aluminate and the oxide metallic

  being intimately mixed and heated to a temperature

  they form an inter-oxide compound (20) in which the different components form an alkaline earth metal oxide compound which can be characterized by the formula Ba OA 1203 MO 2, this cathode block (22) comprising in addition, an electron-emitting surface (22a) having a shape which exposes the filled gaps and the particle-like matrix of the cathode block so as to define, during operation, a set of exposed parts in aluminate of

  alkaline earth metal throughout the bare surface of the

* This cathode can be heated up to

  electron emission temperatures at which the metal oxide

  that and alkaline earth metal aluminate give rise to

  interaction during operation, so as to reduce

  the extraction energy for the emission of electrons at

  calf of the surface (22 a), whereas the emission-enhancing metal can not be sprayed from the surface

  because of its structural incorporation into the

  impregnation and in the interstices of the building block

  method. 2 improved cathode according to claim 1,

  characterized in that the interstices teparis throughout the vo-

  lume of the matrix represent approximately 20% to 25%

the volume of it.

  3 improved cathode according to claim 1, characterized in that the alkaline earth metal aluminate

  consists of a calcium-barium aluminate.

  Microwave electronic tube, characterized in that it comprises: an improved cathode (22) intended to produce, when heated, an electron beam

  (34) having a high current density, this cathode

  taking a matrix of agglomerated metal particles (10, 12)

  between which interstices are formed which are

  dispersed almost uniformly throughout the matrix.

  this and which define in it an initial porosity

  predetermined, this matrix consisting of particles of

  tal (10, 12) selected from the group consisting of tungsten and molybdenum or mixtures thereof, said matrix being compressed and treated so as to bring the particles (10, 12) into intimate contact with each other, said particles being together in their contact regions, the particles nevertheless retaining their discrete character to form the

  interstices and to define an important empty volume

  distributed throughout the matrix, and a matter of

  an electron-emitting compound which fills the interstices of the matrix to form with it a solid cathode block (22) of negligible porosity, this impregnating material

  emitter comprising an alkali metal aluminate

  lino-terrestrial, comprising at least barium oxide, and further containing at least one metal oxide (MO 2) whose metal is selected from the group consisting of iridium and rhenium, this alkaline earth metal aluminate and the oxide

  metal being intimately mixed and heated to a temperature

  wherein an interoxide compound (20) is formed in which the individual components form an alkaline earth metal oxide compound (which can be characterized by the formula BaOA 12036 M 02), the cathode block having -

  an electron-emitting surface having a shape which exposes the filled gaps and the particulate matrix of the cathode block so as to define in operation a set of alkaline earth metal aluminate bare parts; , over the entire exposed surface of the matrix, means for heating the cathode to an electron emission temperature, to which the metal

  emission improvement and the alkali metal aluminate

  no-earths give rise to an interaction during the

  in order to reduce the extraction energy for the emission of electrons at that surface, whereas said metal can not be sprayed from the surface due to its structural incorporation into the impregnation and throughout the cathode block; an anode (38) spaced apart from the cathode to accelerate the emitted electrons to form an electron beam (34) directed toward the anode; an interaction structure (50, 51, 52;

  58, 59, 60) arranged in the tube to produce a modula-

  electron beam at the microwave; and means (64) for extracting microwave energy from

of the tube.

  Microwave tube according to Claim 4, characterized in that the interaction structure (50, 51, 52; 58, 59, 60) is of the klystron type and the modulation is

therefore a modulation of speed.

  6 Electronic tube, characterized in that

  takes: an improved cathode (22) for producing, when heated, an electron beam (34) having a high current density, said cathode comprising a matrix of agglomerated metal particles (10, 12) forming

  between them interstices which are dispersed in a practically

  tically uniform throughout the matrix and which define

  in it a predetermined initial porosity, this ma-

  trice consisting of metal particles (10, 12) selected from the group consisting of tungsten and molybdenum or mixtures thereof, said matrix being compressed and treated to bring the particles into intimate contact with each other so that the particles be linked together

  in their contact regions, the particles retaining

  less their discrete character to form the interstices between them and to provide a large void volume throughout the matrix, and an electron-emitting impregnation material which fills the interstices of the matrix for

  form with it a cathode block full of neonatal porosity

  gligeable, the electron-emitting material comprising an alkaline earth metal aluminate comprising at least barium oxide, and further containing at least one emission-improving metal oxide (MO 2), the metal is

  selected from the group consisting of iridium and rhenium,

  this alkaline earth metal aluminate and the metal oxide

  being intimately mixed and heated to a

  structure in which an interoxide compound (20) is formed in which the various components form an alkaline earth metal oxide compound (which can be characterized by the

  formula Ba O A 1203 M 02), the cathode block comprising in

  an electron-emitting surface (22a) having a shape

  which exposes the interstices filled and the particle matrix

  the blocks to define, during operation, an

  appears to be bare parts of alkaline earth metal aluminate,

  throughout the bare surface of the matrix, this cathode can

  to be heated up to a heat emission temperature

  trons to which the metal oxide and the alkaline earth metal aluminate interact during operation, so as to reduce the extraction energy for the emission of electrons to said surface, while the metal of improvement of the emission can not be pulverized

  from the surface, because of its structural incorporation

  in the impregnation material and in all

  terstices of the cathode block; means (28) for

  to heat the cathode to a heat emission temperature

  trons to which the emission enhancement metal and

  alkaline earth metal aluminate give rise to a

  during operation, in order to reduce the energy

  extraction unit for the emission of electrons to said surface, whereas this metal can not be sprayed from the surface due to its structural incorporation throughout the cathode block; an anode (38) spaced from the cathode to accelerate the electrons to form an electron beam (34) directed toward the anode; and means

  (44, 62, 50, 51, 52, 58, 59, 60) for controlling the movement of

of the electron beam.