JP2014203799A - Impregnation type cathode structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve the joint strength between a heater and support mediums in an impregnation type cathode structure.SOLUTION: An impregnation type cathode structure 1 includes: a cathode base material 10; a support external cylinder 24; a support internal cylinder 26; a protruding part 30; and a heater 40. The cathode base material 10 includes an electron emission surface 12 impregnated with an electronic emissive material. The support external cylinder 24 extends from a rear surface 14 of the electron emission surface 12 of the cathode base material 10. The support internal cylinder 26 coaxially extends with the support external cylinder 24 to form an annular storage space 22 with the support external cylinder 24. The protruding part 30 protrudes from the support internal cylinder 26 toward the support external cylinder 24, and a through hole which penetrates through the protruding part 30 in an axial direction of the support internal cylinder 26 is formed in the protruding part 30. The heater 40 has a linear shape, is housed in the storage space 22, and is fixed by one end part inserted into the through hole 31 and penetrating through the protruding part 30.

Description

  Embodiments generally relate to an impregnated cathode assembly used in an electron gun of a microwave electron tube such as a klystron or a gyrotron.

  Currently, microwave electron tubes such as klystrons used in nuclear fusion and particle accelerators have reached the megawatt level, and higher output is desired. Therefore, in such a high-power microwave electron tube, an electron gun using an impregnated cathode instead of an oxide cathode is used.

  An impregnated cathode assembly that is a cathode assembly used in an electron gun of a klystron has a cathode base, a support, a heater, an embedding material, and the like. The cathode substrate is made of porous tungsten (W) and is formed into a disk shape. The cathode base is formed with an electron emission surface that is recessed in a curved shape. The holes of the cathode substrate are impregnated with an electron emitting material.

  In addition to supporting the cathode base, the support plays a role of storing the heater and the embedded material in a storage space formed inside. The support has a support outer cylinder and a support inner cylinder made of molybdenum (Mo). The support inner cylinder is arranged coaxially (concentrically) with the support outer cylinder in the cylinder of the support outer cylinder so that an annular storage space is formed between the support outer cylinder and the support outer cylinder.

  The cathode substrate is brazed to one end of the support outer cylinder and the support inner cylinder using a ruthenium-molybdenum (Ru-Mo) alloy. The heater plays the role of heating the cathode substrate through the filling material. The heater is a tungsten (W) wire wound in a coil shape, and is stored in the storage space. One end of the heater is joined to the outer wall of the supporting inner cylinder, and the heater and the cathode base are at the same potential.

  The filling material plays a role of holding the heater stored in the storage space in addition to transferring heat from the heater to the cathode base. The embedding material is an alumina sintered body, and the storage space in which the heater is stored is filled without a gap.

Japanese Patent Laid-Open No. 2001-256883 Japanese Examined Patent Publication No. 7-66747 JP 2011-129384 A

  In the impregnated cathode assembly, the support and the embedding material have different coefficients of thermal expansion. For this reason, due to the heating of the heater, a difference in thermal expansion occurs between the support and the embedding material, and stress is applied to the joint portion between one end of the heater and the outer wall of the support inner cylinder.

  It is difficult to arrange the heater at a predetermined position in the storage space with sufficient accuracy. If the contact area between one end of the heater and the outer wall of the supporting inner cylinder becomes small, the bonding strength cannot be ensured. If sufficient bonding strength cannot be ensured, the heater may be disconnected from the support inner cylinder due to repeated ON / OFF of the heater.

  In order to ensure the bonding strength between the heater and the support inner cylinder, a method has been proposed in which a recess is formed in the outer wall of the support inner cylinder and one end of the heater is welded to the recess. Further, a method has been proposed in which a protrusion is formed on the end surface of the supporting inner cylinder, and one end of the heater is welded to the protrusion.

  However, if the concave portion of the supporting inner cylinder having a large heat capacity or the gap between the end projecting portion of the supporting inner cylinder and one end of the heater is increased, the welding area may be reduced, and the strength of the joint may be reduced.

  Therefore, the embodiment aims to further increase the bonding strength between the heater and the support of the impregnated cathode assembly.

  In order to achieve the above object, an impregnated-type cathode assembly according to an embodiment includes a cathode substrate having an electron emission surface impregnated with an electron-emitting material, a support outer cylinder extending from the back surface of the electron emission surface of the cathode substrate, A support inner cylinder that extends coaxially from the back surface with the support outer cylinder to form an annular storage space between the support outer cylinder, and either the support outer cylinder or the support inner cylinder toward the other A fixing portion that protrudes and has a through-hole that penetrates in the axial direction of the support outer cylinder and the support inner cylinder, and is housed in the storage space and has one end that passes through the through-hole and is fixed to the fixing portion. And a linear heater.

It is a side view which shows a part of impregnation-type cathode structure by 1st Embodiment in a cross section. It is the perspective view which expanded the fitting part vicinity of the heater and support inner cylinder of the impregnation type cathode structure by 1st Embodiment. It is a fragmentary longitudinal cross-sectional view of the impregnated-type cathode assembly according to the second embodiment. It is the perspective view which expanded the protrusion part vicinity of the impregnation type | mold cathode structure of 2nd Embodiment. It is a perspective view of the ring in the modification of 2nd Embodiment.

  Hereinafter, impregnated-type cathode assemblies according to some embodiments will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or similar structure, and the overlapping description is abbreviate | omitted.

[First Embodiment]
FIG. 1 is a side view showing a part of the impregnated-type cathode assembly according to the first embodiment in cross section.

The impregnated-type cathode assembly 1 according to this embodiment is a cathode assembly used for an electron gun of a klystron. The impregnated cathode assembly 1 includes a cathode substrate 10, a support 20, a heater 40, an embedding material 50, reflectors 60 and 62, and a reflector cylinder 66. The cathode substrate 10 is made of, for example, porous tungsten (W) having a porosity of 15 to 20%. The cathode substrate 10 is molded into a disk shape having a diameter of 70 mm, for example. The cathode substrate 10 is formed with an electron emission surface 12 that is recessed into a curved surface with a predetermined curvature. The holes of the cathode substrate 10 are impregnated with an electron emitting material made of, for example, barium oxide (BaO), calcium oxide (CaO), and aluminum oxide (Al ₂ O ₃ ).

  The electron emission surface 12 is likely to be clogged with holes in the cathode substrate 10 during processing. This clogging may not sufficiently impregnate the holes with the electron emitting material. In order to prevent this, it is preferable to impregnate the pores of the cathode base 10 with plastic before processing the electron emission surface 12 and to scatter the plastic after processing the electron emission surface 12. For example, when the cathode substrate 10 is heated in a hydrogen atmosphere or under vacuum, the plastic impregnated in the cathode substrate 10 is scattered. After the plastic is thus scattered, the holes of the cathode substrate 10 may be impregnated with an electron emitting substance.

  The support 20 has a support outer cylinder 24 and a support inner cylinder 26. The support outer cylinder 24 and the support inner cylinder 26 are each made of molybdenum (Mo) and are formed into a cylindrical shape. The support inner cylinder 26 is disposed coaxially (concentrically) with the support outer cylinder 24 in the cylinder of the support outer cylinder 24 so that an annular storage space 22 is formed between the support outer cylinder 24 and the support outer cylinder 24. The support inner cylinder 26 is molded to have a diameter of 20 mm, an axial length of 20 mm, and a wall thickness of 2 mm, for example. The support 20 supports the cathode substrate 10. In addition, the heater 40 and the embedding material 50 are stored in the storage space 22 formed between the support outer cylinder 24 and the support inner cylinder 26 of the support 20.

  The cathode base 10 is disposed so as to close one end of the storage space 22 and is joined to the same end of the support outer cylinder 24 and the support inner cylinder 26. Specifically, one end of the support outer cylinder 24 and the support inner cylinder 26 and the back surface 14 of the cathode base 10 are brazed using, for example, a ruthenium-molybdenum (Ru-Mo) alloy. Here, the back surface 14 of the cathode substrate 10 is a surface opposite to the electron emission surface 12.

  The heater 40 is a filament formed in a linear shape, for example, a tungsten (W) wire having a diameter of 1.5 mm. An intermediate portion (heat generation portion) 42 of the heater 40 is wound in a coil shape and stored in a storage space 22 formed between the support outer cylinder 24 and the support inner cylinder 26. The winding axis of the heater 40 extends, for example, in the circumferential direction of the support 20.

  The embedding material 50 is, for example, an alumina sintered body, and fills the storage space 22 in which the intermediate portion 42 that is a heat generating portion of the heater 40 is stored without a gap. The heater 40 plays a role of heating the cathode substrate 10 through the filling material 50. The embedding material 50 plays a role of holding the heater 40 stored in the storage space 22 in addition to transferring the heat from the heater 40 to the cathode base 10.

  One end 44 of the heater 40 is electrically connected to the support inner cylinder 26. Therefore, the heater 40, the support 20 and the cathode base 10 are at the same potential.

  The other end 46 of the heater 40 passes through an alumina tube 48 provided at the end of the support 20 away from the cathode base 10 and extends to the outside of the impregnated cathode assembly 1 to be connected to a power supply device (not shown). Has been. The alumina tube 48 is provided to prevent the heater 40 from breaking near the surface of the embedding material 50 and to insulate the heater 40 from a first reflector 60 described later.

  The first reflecting plate 60 is an annular plate body made of molybdenum (Mo), and closes an opening away from the cathode base 10 in the storage space 22 formed between the support outer cylinder 24 and the support inner cylinder 26. Is arranged. The outer edge of the first reflector 60 is joined to the end of the support outer cylinder 24 by arc welding, and the inner edge of the first reflector 60 is joined to the end of the support inner cylinder 26 by arc welding. Yes.

  The second reflecting plate 62 is a disc made of molybdenum (Mo), and is disposed outside the first reflecting plate 60, that is, away from the cathode substrate 10, and is arc-welded through a cylindrical spacer 64. It is joined to the first reflector 60.

  The reflection cylinder 66 is made of a rhenium-molybdenum (Re-Mo) alloy, and is disposed on the outer periphery of the support outer cylinder 24 so as to cover the support outer cylinder 24. The end of the reflecting cylinder 66 closer to the cathode substrate 10 is brazed to the support outer cylinder 24 using a ruthenium-molybdenum-nickel (Ru-Mo-Ni) alloy. An annular flange member 68 is brazed using a Ru—Mo—Ni alloy at the end of the reflecting tube 66 far from the cathode substrate 10. The impregnated-type cathode assembly 1 is fixed to an electron gun portion (not shown) via the flange member 68.

  The first reflecting plate 60, the second reflecting plate 62, and the reflecting cylinder 66 suppress heat release from the storage space 22 of heat generated by the heater 40 to the outside, and increase the heating efficiency of the cathode substrate 10 by radiation.

  FIG. 2 is an enlarged perspective view of the vicinity of the fitting portion between the heater and the supporting inner cylinder of the impregnated-type cathode assembly according to the present embodiment.

  A protruding portion 30 protruding from the side surface of the supporting inner cylinder 26 toward the supporting outer cylinder 24 is provided at the end of the supporting inner cylinder 26 far from the cathode base 10. A round hole 31 penetrating in the axial direction of the support inner cylinder 26 is formed in the protrusion 30. The protrusion 30 is formed integrally with the support inner cylinder 26. A notch 61 is formed at a position corresponding to the protruding portion 30 of the first reflecting plate 60. For example, the projecting portion 30 is formed in a square shape having a side cross section of 2 mm in the projecting direction, and the round hole portion is formed in a diameter of 1.5 mm.

  In addition, the end 44 of the heater 40 opposite to the end 46 connected to the power supply device is inserted through a notch 61 formed in the inner edge of the first reflector 60 to the outside of the embedding material 50. It extends and is inserted and joined to the round hole 31 of the protrusion 30 outside the storage space. In the present embodiment, the end portion 44 of the heater 40 and the protruding portion 30 are joined by, for example, arc welding.

  A method for manufacturing the impregnated-type cathode assembly 1 according to this embodiment will be described. The impregnated-type cathode assembly 1 is manufactured as follows, for example.

  First, the support 20 is placed on the back surface of the cathode base 10 that is not impregnated with the electron emitting substance, and a Ru—Mo alloy is applied to the joint portion between the cathode base 10 and the support 20. At the same time, a Ru—Mo alloy is applied to the back surface 14 of the cathode substrate 10. After the application, the Ru—Mo alloy is dissolved, the cathode base 10 and the support 20 are joined, and a Ru—Mo alloy film is formed on the back surface 14 of the cathode base 10. This Ru—Mo alloy film prevents the electron emitting material from oozing out from the back surface 14 of the cathode substrate 10 into the storage space 22 when the electron emitting material 12 is impregnated from the electron emitting surface 12 of the cathode substrate 10. Is.

  Thereafter, the heater 40 is held at a predetermined position in the storage space 22 formed between the support outer cylinder 24 and the support inner cylinder 26 with a jig, and the storage space 22 is filled with the filling material 50. The filling material 50 can be filled, for example, by adding powdered alumina to an organic solvent containing a binder and stirring the mixture into a storage space 22 and then spraying the organic solvent by drying. Sintering is performed at 1800 to 1850 ° C. in a vacuum or in a hydrogen atmosphere.

  After the filling material 50 is filled, the first reflecting plate 60 is welded to the support 20, and the second reflecting plate 62 is welded to the first reflecting plate 60 via the spacer 64. Further, the reflecting tube 66 is brazed to the support 20. Further, the end portion 44 of the heater 40 is inserted into the round hole portion 31 of the protruding portion 30 to weld the protruding portion.

  Finally, an electron emitting material is placed on the electron emitting surface 12 of the cathode substrate 10, and the electron emitting material is melted at 1600 to 1700 ° C. in a hydrogen atmosphere and impregnated in the cathode substrate 10. Complete.

  According to the present embodiment, the end portion 44 of the heater 40 opposite to the end portion 46 connected to the power supply device extends to the outside of the embedding material 50 and is formed in the support inner cylinder 26 outside the storage space 22. The protruding portion 30 is joined. Therefore, this joining portion is not easily subjected to stress due to a difference in thermal expansion generated between the support inner cylinder 26 and the embedding material 50 during heating, and even if the heater 40 is repeatedly turned on and off, the heater 40 and the support inner cylinder 26 Is difficult to come off. Accordingly, the bonding strength between the heater 40 and the support 20 can be further increased, and a current can be stably supplied to the heater 40.

  In contrast to the conventional impregnated cathode structure in which one end of the heater is joined to the outer wall of the supporting inner cylinder having a large heat capacity, in this embodiment, the end portion 44 of the heater 40 is joined to the protruding portion 30 having a small heat capacity. . Therefore, in this embodiment, the heating amount (welding current) and the heating time at the time of welding can be reduced and the embrittlement of the heater 40 can be suppressed compared to the conventional case.

  Furthermore, according to the present embodiment, the end portion 44 of the heater 40 is joined to the round hole portion 31 of the protruding portion 30 formed in the support inner cylinder 26 outside the storage space 22. Therefore, the joining operation of the heater 40 and the support 20 is facilitated, and contact failure can be further reduced.

[Second Embodiment]
A second embodiment of the impregnated cathode assembly according to the present invention will be described with reference to FIGS.

  FIG. 3 is a partial longitudinal sectional view of an impregnated-type cathode assembly according to the second embodiment. FIG. 4 is an enlarged perspective view of the vicinity of the protruding portion of the impregnated-type cathode assembly of the present embodiment.

  The impregnated-type cathode assembly 2 according to the present embodiment is a cathode assembly used for an electron gun of a gyrotron. The impregnated cathode assembly 2 includes a cathode substrate 10, a support 20, a heater 40, a filling material 50, a reflection plate 60, and a reflection tube 66.

  The support 20 has a support outer cylinder 24, a support inner cylinder 26, and a closing plate 28. The support inner cylinder 26 is disposed coaxially (concentrically) with the support outer cylinder 24 in the cylinder of the support outer cylinder 24 so that an annular storage space 22 is formed between the support outer cylinder 24 and the support outer cylinder 24. The closing plate 28 is disposed so as to block one opening end of the support 20, that is, the end on the same side of the support outer cylinder 24 and the support inner cylinder 26. The support outer cylinder 24, the support inner cylinder 26, and the closing plate 28 are integrally molded.

  The cathode substrate 10 is formed into a ring shape having an inner diameter of 70 mm and an outer diameter of 90 mm, for example. The cathode substrate 10 is brazed to a flange portion 25 formed on the outer periphery of the support outer cylinder 24.

  The storage space 22 formed between the support outer cylinder 24 and the support inner cylinder 26 of the support 20 stores the heater 40 and is filled with the embedding material 50 as in the first embodiment.

  At the end of the support inner cylinder 26, a ring 32 is attached to the side surface of the support inner cylinder 26, and the ring 32 is formed with a round hole portion 31 penetrating in the axial direction of the support inner cylinder 26. Further, the end portion 44 of the heater 40 passes through a notch 61 formed in the inner edge portion of the first reflecting plate 60, extends to the outside of the embedding material 50, and is a round hole of the ring 32 outside the storage space 22. It is joined to the part 31.

  In the present embodiment, the distal end surface of the end portion 44 of the heater 40 and the distal end surface of the ring 32 form approximately the same plane. For example, 20 platinum ribbons 33 having a length of 3 mm, a width of 1 mm, and a thickness of 50 μm are stacked and placed on the tip surface of the end portion 44 of the heater 40 and the tip surface of the round hole portion 31 of the ring 32. Then, the platinum ribbon 33 is melted, and the end portion 44 of the heater 40, the round hole portion 31 and the ring 32 of the ring 32, and the support inner cylinder 26 are electrically connected.

  Also according to this embodiment, the same effect as that of the first embodiment can be obtained.

  FIG. 5 is a perspective view of a ring in a modification of the present embodiment.

  In this modification, the ring 32 attached to the support inner cylinder 26 is formed by forming a notch in the round hole portion 31. The ring 32 is separated in the circumferential direction by this notch. If the inner diameter of the round hole portion 31 is formed slightly smaller than the end portion 44 of the heater 40, the end portion 44 of the heater 40 can be supported by the spring force of the ring 32.

[Other Embodiments]
Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  For example, in the first embodiment related to the impregnated cathode assembly 1 for klystrons, the end portion 44 of the heater 40 and the round hole portion 31 of the protruding portion 30 are joined by arc welding, but in the second embodiment, As explained, it may be joined by dissolving the platinum ribbon 33. In the second embodiment of the impregnated cathode assembly 2 for the gyrotron, the end 44 of the heater 40, the round hole 31 of the ring 32, the ring 32, and the support inner cylinder 26 dissolve the platinum ribbon 33. However, as described in the first embodiment, they may be joined by arc welding.

  The protruding portion 30 having the round hole portion 31 in the first embodiment does not need to be molded integrally with the support inner cylinder 26, and may be joined to one end surface of the support inner cylinder 26 by, for example, brazing. Good. Moreover, the edge part 44 of the heater 40, the round hole part 31 and the ring 32 of the protrusion part 30, and the support inner cylinder 26 may be joined by brazing, for example.

  The joining of the end portion 44 of the heater 40 described in the first embodiment and the second embodiment is performed by the support inner cylinder 26, but the same effect can be obtained even if it is performed by the support outer cylinder 24.

DESCRIPTION OF SYMBOLS 1 ... Impregnation-type cathode structure, 2 ... Impregnation-type cathode structure, 10 ... Cathode base | substrate, 12 ... Electron emission surface, 14 ... Back surface, 20 ... Support body, 22 ... Storage space, 24 ... Support outer cylinder, 25 ... Flange part, 26 ... Support inner cylinder, 28 ... Blocking plate, 30 ... Projection part, 31 ... Round hole part, 32 ... Ring, 33 ... Platinum ribbon, 40 ... Heater, 42 ... Heat generation part, 44 ... End part, 46 ... End part, 48 ... Alumina tube, 50 ... embedding material, 60 ... first reflection plate, 61 ... notch, 62 ... second reflection plate, 64 ... spacer, 66 ... reflection tube, 68 ... flange member

Claims (5)

A cathode substrate having an electron emission surface impregnated with an electron emitting material;
A support outer cylinder extending from the back surface of the electron emission surface of the cathode substrate;
A support inner cylinder extending coaxially with the support outer cylinder from the back surface to form an annular storage space between the support outer cylinder, and
A fixing portion in which a through hole that protrudes from one of the support outer cylinder and the support inner cylinder toward the other and penetrates in the axial direction of the support outer cylinder and the support inner cylinder;
A linear heater housed in the housing space and having one end passing through the through hole and fixed to the fixed part;
An impregnated cathode structure comprising:   2. The impregnated-type cathode assembly according to claim 1, wherein the fixing portion is a protruding portion that protrudes from one of the support outer cylinder and the support inner cylinder toward the storage space.   2. The impregnated-type cathode assembly according to claim 1, wherein the fixing portion is a ring fixed to one of an inner side surface of the support outer cylinder and an outer side surface of the support inner cylinder.   4. The impregnated-type cathode assembly according to claim 3, wherein the ring is separated in the circumferential direction by a notch at a portion where the through hole is formed. The impregnated-type cathode assembly according to any one of claims 1 to 4, wherein the fixed portion and one end portion of the heater are joined by platinum.

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