EP0534762A1 - Dielectric support rod for a traveling-wave tube - Google Patents

Dielectric support rod for a traveling-wave tube Download PDF

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Publication number
EP0534762A1
EP0534762A1 EP92308726A EP92308726A EP0534762A1 EP 0534762 A1 EP0534762 A1 EP 0534762A1 EP 92308726 A EP92308726 A EP 92308726A EP 92308726 A EP92308726 A EP 92308726A EP 0534762 A1 EP0534762 A1 EP 0534762A1
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EP
European Patent Office
Prior art keywords
support rod
dielectric support
traveling
dielectric
wave tube
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP92308726A
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German (de)
French (fr)
Inventor
Takayoshi Konishi
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NEC Corp
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NEC Corp
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Filing date
Publication date
Application filed by NEC Corp filed Critical NEC Corp
Publication of EP0534762A1 publication Critical patent/EP0534762A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/16—Circuit elements, having distributed capacitance and inductance, structurally associated with the tube and interacting with the discharge
    • H01J23/24—Slow-wave structures, e.g. delay systems
    • H01J23/26—Helical slow-wave structures; Adjustment therefor

Definitions

  • the present invention relates to a dielectric support rod of a traveling-wave tube and, more particularly, to an anti-charge structure of the dielectric support rod.
  • a traveling-wave tube has a RF circuit for causing a RF component and an electron beam to interact with each other so as to amplify the RF component.
  • a RF circuit is supported in a vacuum sealing metal pipe generally by three dielectric support rods.
  • Figs. 1A and 1B show the structure of a RF circuit used in a conventional helix type traveling-wave tube.
  • a RF circuit 2 is supported in a vacuum sealing metal pipe 3 by dielectric support rods 1. More specifically, the RF circuit 2 is generally supported by the three dielectric support rods 1 spaced apart from each other at an equal angular interval of 120 ° so that the RF circuit 2 is supported in the metal pipe 3.
  • Figs. 2A and 2B show a conventional dielectric support rod.
  • the conventional dielectric support rod material is alumina (Al2O3) or beryllia (BeO).
  • BeO beryllia
  • boron nitride (BN) having a low dielectric constant has been used. Boron nitride, however, may be charged by an electron beam passing through the RF circuit to cause a change in potential, thereby forming an unstable electron beam track. In the worst case,the RF circuit may be damaged.
  • a thin carbon coating is formed on the surface of a boron nitride dielectric support rod 1 to cause charges to flow to the RF circuit or the vacuum sealing metal pipe through the coating layer according to a conventional technique.
  • This carbon coating causes an increase in RF loss to decrease the output or gain of the traveling-wave tube, resulting in inconvenience.
  • a dielectric support rod for a traveling-wave tube which supports an RF circuit of said traveling-wave tube, and has a coating thereon, characterized in that the coating on said rod comprises a dielectric having a secondary electron emission ratio of not less than 1 when primary electrons of eE (eV) are incident thereon, where E (V) is the voltage between a cathode and said RF circuit of said traveling-wave tube, and e (Coul) is the charge on an electron.
  • the dielectric to be coated on the surface is preferably alumina or beryllia.
  • the dielectric support rod Since the secondary electron emission ratio is 1 or more, the dielectric support rod is not negatively charged. Even if the dielectric support rod is positively charged, the potential of the dielectric support rod is increased to re-attract secondary electrons to the dielectric support rod, resulting in a small amount of positive charge. This positive charge does not disturb the track of the electron beam passing through the RF circuit.
  • charging is also suppressed by means of the outer coating layer even when electron beam bombardment occurs. Also, the peripheral potential is not much changed to prevent disturbance of the electron beam track.
  • the Joule loss is eliminated to prevent a decrease in gain and output of the traveling-wave tube.
  • FIG. 3A and 3B show the first embodiment of the present invention.
  • a thin alumina coating 11 having a thickness of about 5nm is formed on a boron nitride dielectric support rod 10.
  • Fig. 4 shows the secondary electron emission ratios of boron nitride and alumina.
  • a voltage E (V) between a cathode and a RF circuit of a traveling-wave tube is 10 kV.
  • V a voltage between a cathode and a RF circuit of a traveling-wave tube
  • electrons emitted from the cathode and accelerated pass through the RF circuit with a kinetic energy of 10 keV, and some electrons are incident on the dielectric support rod.
  • the dielectric support rod consists only of boron nitride
  • the secondary electron emission ratio of the dielectric support rod is less than 1, as is apparent from Fig. 4.
  • the dielectric support rod accumulates electrons and is negatively charged to decrease the peripheral potential. Therefore, the track of the electron beam passing through the RF circuit becomes unstable.
  • the dielectric support rod has a structure obtained by forming an aluminum coating on boron nitride, as shown in Figs. 3A and 3B, the secondary electron emission ratio is 1 or more even if electrons having a kinetic energy of 10 keV are incident, as is apparent from Fig. 4.
  • the dielectric support rod is not negatively charged.
  • the dielectric support rod may be positively charged, the potential of the positively charged dielectric support rod is increased to re-attract the secondary electrons.
  • the positive charge amount is small enough not to disturb the track of the electron beam passing through the RF circuit.
  • the dielectric support rod having the structure obtained by coating alumina on boron nitride charging is also suppressed by electron beam bombardment, and the peripheral potential is not much changed, thereby preventing the disturbance of the electron beam.
  • alumina is a dielectric, a Joule loss caused by a carbon coating can be prevented, and a decrease in gain and output of the traveling-wave tube can be prevented.
  • the second embodiment of the present invention exemplifies a beryllia coating formed on a boron nitride dielectric support rod in place of an alumina coating.
  • a beryllia coating formed on a boron nitride dielectric support rod in place of an alumina coating.
  • charging is expected to be prevented, and the disturbance of the electron beam track is also expected to be prevented, as can be apparent from Fig. 4.
  • beryllia has a larger heat conductivity and a smaller dielectric constant than those of alumina, the heat dissipation effect and efficiency of the traveling-wave tube better than those in the first embodiment can be expected.
  • alumina and beryllia dielectric coatings are formed in accordance with CVD (chemical vapour deposition) or ion plating.

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  • Microwave Tubes (AREA)

Abstract

A dielectric support rod for a traveling-wave tube has a core (10) of boron nitride coated with a dielectric (11). The dielectric has a secondary electron emission ratio of 1 or more, when primary electrons of eE (eV) are incident thereon, where E (V) is the voltage between the cathode and the RF circuit of the traveling-wave tube, and e (Coul) is the charge on an electron. The dielectric to be coated on the surface can be alumina or beryllia. The rod does not then become negatively charged such as to cause the track of the electrons to become unstable.
Figure imgaf001

Description

    BACKGROUND OF THE INVENTION FIELD OF THE INVENTION
  • The present invention relates to a dielectric support rod of a traveling-wave tube and, more particularly, to an anti-charge structure of the dielectric support rod.
    • DESCRIPTION OF THE PRIOR ART
  • A traveling-wave tube has a RF circuit for causing a RF component and an electron beam to interact with each other so as to amplify the RF component. In a helix or ring loop type traveling-wave tube, a RF circuit is supported in a vacuum sealing metal pipe generally by three dielectric support rods.
  • Figs. 1A and 1B show the structure of a RF circuit used in a conventional helix type traveling-wave tube. A RF circuit 2 is supported in a vacuum sealing metal pipe 3 by dielectric support rods 1. More specifically, the RF circuit 2 is generally supported by the three dielectric support rods 1 spaced apart from each other at an equal angular interval of 120 ° so that the RF circuit 2 is supported in the metal pipe 3. Figs. 2A and 2B show a conventional dielectric support rod. The conventional dielectric support rod material is alumina (Al₂O₃) or beryllia (BeO). However, in recent years, in order to improve efficiency of the traveling-wave tube, boron nitride (BN) having a low dielectric constant has been used. Boron nitride, however, may be charged by an electron beam passing through the RF circuit to cause a change in potential, thereby forming an unstable electron beam track. In the worst case,the RF circuit may be damaged.
  • In order to prevent boron nitride from being charged, a thin carbon coating is formed on the surface of a boron nitride dielectric support rod 1 to cause charges to flow to the RF circuit or the vacuum sealing metal pipe through the coating layer according to a conventional technique.
  • This carbon coating causes an increase in RF loss to decrease the output or gain of the traveling-wave tube, resulting in inconvenience.
    • SUMMARY OF THE INVENTION
  • According to the present invention, there is provided a dielectric support rod for a traveling-wave tube, which supports an RF circuit of said traveling-wave tube, and has a coating thereon, characterized in that the coating on said rod comprises a dielectric having a secondary electron emission ratio of not less than 1 when primary electrons of eE (eV) are incident thereon, where E (V) is the voltage between a cathode and said RF circuit of said traveling-wave tube, and e (Coul) is the charge on an electron.
  • The dielectric to be coated on the surface is preferably alumina or beryllia.
  • Since the secondary electron emission ratio is 1 or more, the dielectric support rod is not negatively charged. Even if the dielectric support rod is positively charged, the potential of the dielectric support rod is increased to re-attract secondary electrons to the dielectric support rod, resulting in a small amount of positive charge. This positive charge does not disturb the track of the electron beam passing through the RF circuit.
  • In addition, charging is also suppressed by means of the outer coating layer even when electron beam bombardment occurs. Also, the peripheral potential is not much changed to prevent disturbance of the electron beam track.
  • The Joule loss is eliminated to prevent a decrease in gain and output of the traveling-wave tube.
  • The above and other objects, features, and advantages according to the present invention will be apparent to those skilled in the art from the following detailed description of the preferred embodiments conforming with the principle of the present invention in conjunction with the accompanying drawings.
    • BRIEF DESCRIPTION OF THE DRAWINGS
    • Figs. 1A and 1B are a longitudinal sectional view and a side view, respectively, showing the structure of a RF circuit portion of a traveling-wave tube;
    • Figs. 2A and 2B are a front view and a cross-sectional view, respectively, showing a conventional dielectric support rod;
    • Figs. 3A and 3B are a front view and a sectional view, respectively, showing a dielectric support rod according to an embodiment of the present invention; and
    • Fig. 4 is a graph showing the secondary electron emission ratio of each dielectric as a function of the primary electron incident energy.
    DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • Several preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings (Figs. 3A, 3B, and 4).
  • Fig. 3A and 3B show the first embodiment of the present invention. A thin alumina coating 11 having a thickness of about 5nm is formed on a boron nitride dielectric support rod 10.
  • Fig. 4 shows the secondary electron emission ratios of boron nitride and alumina.
  • Assume that a voltage E (V) between a cathode and a RF circuit of a traveling-wave tube is 10 kV. In this case, electrons emitted from the cathode and accelerated pass through the RF circuit with a kinetic energy of 10 keV, and some electrons are incident on the dielectric support rod. When the dielectric support rod consists only of boron nitride, the secondary electron emission ratio of the dielectric support rod is less than 1, as is apparent from Fig. 4. The dielectric support rod accumulates electrons and is negatively charged to decrease the peripheral potential. Therefore, the track of the electron beam passing through the RF circuit becomes unstable.
  • On the other hand, when the dielectric support rod has a structure obtained by forming an aluminum coating on boron nitride, as shown in Figs. 3A and 3B, the secondary electron emission ratio is 1 or more even if electrons having a kinetic energy of 10 keV are incident, as is apparent from Fig. 4. The dielectric support rod is not negatively charged. Although the dielectric support rod may be positively charged, the potential of the positively charged dielectric support rod is increased to re-attract the secondary electrons. The positive charge amount is small enough not to disturb the track of the electron beam passing through the RF circuit.
  • In the dielectric support rod having the structure obtained by coating alumina on boron nitride, charging is also suppressed by electron beam bombardment, and the peripheral potential is not much changed, thereby preventing the disturbance of the electron beam. In addition, since alumina is a dielectric, a Joule loss caused by a carbon coating can be prevented, and a decrease in gain and output of the traveling-wave tube can be prevented.
  • The second embodiment of the present invention exemplifies a beryllia coating formed on a boron nitride dielectric support rod in place of an alumina coating. When the beryllia coating is used in a traveling-wave tube as in the first embodiment, charging is expected to be prevented, and the disturbance of the electron beam track is also expected to be prevented, as can be apparent from Fig. 4. In addition, since beryllia has a larger heat conductivity and a smaller dielectric constant than those of alumina, the heat dissipation effect and efficiency of the traveling-wave tube better than those in the first embodiment can be expected.
  • Note that the alumina and beryllia dielectric coatings are formed in accordance with CVD (chemical vapour deposition) or ion plating.

Claims (5)

  1. A dielectric support rod for a traveling-wave tube, which supports an RF circuit of said traveling-wave tube, and has a coating thereon, characterized in that the coating on said rod (10) comprises a dielectric (11) having a secondary electron emission ratio of not less than 1 when primary electrons of eE (eV) are incident thereon, where E (V) is the voltage between a cathode and said RF circuit of said traveling-wave tube, and e (Coul) is the charge on an electron.
  2. A dielectric support rod according to claim 1, wherein the dielectric to be coated on said surface is alumina.
  3. A dielectric support rod according to claim 1, wherein the dielectric to be coated on said surface is beryllia.
  4. A dielectric support rod according to claim 1, 2 or 3, wherein the rod is formed of boron nitride.
  5. A traveling-wave tube containing an RF circuit supported by one or more dielectric support rods, the or each dielectric support rod being a dielectric support rod in accordance with any of claims 1 to 4.
EP92308726A 1991-09-27 1992-09-24 Dielectric support rod for a traveling-wave tube Withdrawn EP0534762A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP248666/91 1991-09-27
JP24866691A JPH0589788A (en) 1991-09-27 1991-09-27 Dielectric support for travelling wave tube

Publications (1)

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EP0534762A1 true EP0534762A1 (en) 1993-03-31

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5495144A (en) * 1993-02-03 1996-02-27 Nec Corporation Helical slow-wave circuit assembly with reduced RF losses
FR2883409A1 (en) * 2005-03-18 2006-09-22 Thales Sa Travelling-wave tube fabricating method, involves vacuum annealing insulating ceramic supports, of helix, covered with carbon-boron layer and thin protection alumina layer at specific temperature

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08111182A (en) 1994-08-17 1996-04-30 Toshiba Corp Slow-wave circuit structure for traveling wave tube and its manufacture
JP2006134751A (en) * 2004-11-08 2006-05-25 Nec Microwave Inc Electron tube
JP5310062B2 (en) * 2009-02-13 2013-10-09 トヨタ自動車株式会社 Plasma ignition device
CN114538933B (en) * 2020-11-24 2022-11-22 娄底市安地亚斯电子陶瓷有限公司 Method for manufacturing travelling wave tube clamping rod

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH326748A (en) * 1953-12-10 1957-12-31 Siemens Ag Waveguide arrangement for traveling wave tubes
US3466494A (en) * 1968-05-01 1969-09-09 Siemens Ag Traveling wave tube with delay line supports having a lossy layer and an insulation layer
DE3235753A1 (en) * 1982-09-27 1984-03-29 Siemens AG, 1000 Berlin und 8000 München Travelling wave tube having a helical delay line
FR2646732A1 (en) * 1989-05-04 1990-11-09 Raytheon Co HIGH FREQUENCY AMPLIFIER HAVING SLOW WAVE STRUCTURE
EP0402549A1 (en) * 1984-12-18 1990-12-19 Thomson-Csf Travelling-wave tube with a helical delay line made of boron nitride and attached to the vacuum tube

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH326748A (en) * 1953-12-10 1957-12-31 Siemens Ag Waveguide arrangement for traveling wave tubes
US3466494A (en) * 1968-05-01 1969-09-09 Siemens Ag Traveling wave tube with delay line supports having a lossy layer and an insulation layer
DE3235753A1 (en) * 1982-09-27 1984-03-29 Siemens AG, 1000 Berlin und 8000 München Travelling wave tube having a helical delay line
EP0402549A1 (en) * 1984-12-18 1990-12-19 Thomson-Csf Travelling-wave tube with a helical delay line made of boron nitride and attached to the vacuum tube
FR2646732A1 (en) * 1989-05-04 1990-11-09 Raytheon Co HIGH FREQUENCY AMPLIFIER HAVING SLOW WAVE STRUCTURE

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5495144A (en) * 1993-02-03 1996-02-27 Nec Corporation Helical slow-wave circuit assembly with reduced RF losses
FR2883409A1 (en) * 2005-03-18 2006-09-22 Thales Sa Travelling-wave tube fabricating method, involves vacuum annealing insulating ceramic supports, of helix, covered with carbon-boron layer and thin protection alumina layer at specific temperature

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