Classifications

• • 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
  • H01J23/02—Electrodes; Magnetic control means; Screens
  • H01J23/027—Collectors
  • H01J23/0275—Multistage collectors

Definitions

• the invention relates to amplifier electronic tubes operating at microwave frequencies. It applies more particularly to traveling wave tubes (TOP) also called TWT (from the English Traveling Wave Tube), and it is therefore about such a tube that it will be described.
• TOP traveling wave tubes
• TWT from the English Traveling Wave Tube
• Such tubes are used for example for the transmission of telecommunication signals between the earth and the satellites. They also serve as power transmitters in radars.
• a TOP is a vacuum tube using the principle of the interaction between an electron beam and a microwave electromagnetic wave, to transmit to the microwave wave part of the energy contained in the beam of electrons, so as to obtain at the outlet of the tube a microwave wave of energy greater than that of the wave injected at the inlet of the tube.
• Figure 1 recalls the general principle of a TOP.
• the TOP shown is a propeller TOP, but other types of TOP such as the TOPs with coupled cavities, the TOPs with guides folded in meanders, etc., are just as well affected by the invention.
• the TOP comprise an elongated tubular sheath 10 in which the vacuum is created, with at a first end an electron gun 11 emitting an electron beam 12 and, at a second end, a collector 14; the collector collects the electrons which have given up part of their initial energy to the electromagnetic wave that we want to amplify.
• the electron beam 12 is substantially cylindrical over almost the entire length of the tube between the barrel 11 and the collector 14 along an axis 15. This cylindrical beam shape is obtained on the one hand thanks to the shape of a cathode 16 electron gun 11 (converging cathode in the shape of a bowl), and on the other hand by means of magnetic focusing provided over the entire length of the sheath 10 between the outlet of the electron gun 11 and the inlet of the collector 14.
• the cathode 16 which emits the electron beam 12.
• These focusing means comprise for example annular permanent magnets 18 magnetized axially and magnetization alternating from one magnet to the next; these magnets surround the sheath 10 and are separated from each other by pole pieces 20 with high magnetic permeability.
• the electron beam 12 passes inside a helical conductive structure 22 along which the microwave electromagnetic wave to be amplified circulates; the amplification of microwave energy occurs by interaction between this wave and. the electron beam 12 passing through the center thereof.
• the propeller is used to slow down the microwave wave, so that its speed, along the axis 15 of the electron beam 12, is substantially equal to that of the electron beam 12.
• a power signal to be amplified Pe is injected at one end of the conductive helical structure 22 through a plug and a window 24 inside the sheath 10.
• An amplified power signal Ps is extracted at another end of the helical conductive structure 22 through a plug and a window 26.
• V 0 represents a voltage between the cathode 16 and the collector 14 and l 0 represents the current flowing in the cathode 16.
• the efficiency ⁇ is generally of the order of 20 to 30%.
• the electronic tube generally comprises, at the level of the manifold 14, a radiator not shown in FIG. 1. This radiator is for example cooled by circulation of a liquid or gaseous fluid.
• part of the current l 0 coming from the cathode 16, flows in the conductive helical structure 22 as shown in the figure
• the collector 14 is connected to the positive pole 28 of a DC voltage source 30.
• the helical conductive structure is also connected to the positive pole 28.
• the negative pole 32 of the DC voltage source 30 is connected to the cathode 16.
• the electron beam 12 develops between the cathode 16 and the collector 14.
• a current of 1A is obtained from the cathode 16 in the electron beam 12 and a power Ps of 2 kW at the output of the conductive helical structure 22.
• the return current between the collector 14 and the pole 28 is 0.99 A and the current between the conductive helical structure 22 and the pole 28 is 0.01.
• the yield is then expressed:
• the efficiency of an electronic tube can be improved by using two voltage sources.
• This alternative is shown in FIG. 3.
• a first DC voltage source 34 for example of 10 kV is connected between the cathode 16 and the conductive helical structure 22 and a second DC voltage source 36 whose voltage is lower than that of the first voltage source, for example 6 kV is connected between the collector 14 and the cathode 16.
• the efficiency is then expressed:
• the collector 14 comprises several electrodes brought to different potentials.
• the purpose of these different electrodes is to slow down the electrons before they hit the walls of the electrodes.
• the heat dissipated in the collector 14 is lower and the efficiency ⁇ increases.
• FIG. 4 An example of such a collector is shown in FIG. 4.
• the DC voltage source 34 of 10 kV is connected between the helical conductive structure 22 and the cathode 16.
• a current of 0.1 A flows through the voltage source 34.
• a DC voltage source 38 for example 6 kV, is connected between a first electrode 40 and the cathode 16. A current of 0.4 A flows in the voltage source 38.
• a DC voltage source 42 for example of 4 kV is connected between a second electrode 44 and the cathode 16. A current of 0.48 A flows in the voltage source 42.
• a last voltage source 46 for example of 1 kV is connected between a third electrode 48 and the cathode 16. A current of 0.01 A flows through the voltage source 46.
• the three electrodes 40, 44 and 48, belonging to the collector 14, are arranged so that the electrode 40, subjected to the highest voltage relative to cathode 16, that is to say closest to cathode 16 and electrode 48, subjected to the weakest voltage compared to cathode 16 or furthest from cathode 16. Still assuming that the power Ps or 2 kW, the output is expressed as follows:
• This collector structure 14 comprising several electrodes is called a depressed collector. It is understood that the number of electrodes and the digital values of the currents, voltages and powers are given only by way of example and that the invention is not limited to these examples.
• the last electrode has a small potential difference compared to cathode 16
• the kinetic energy of the electrons which bombards it is still high and creates heat which it is necessary to evacuate.
• the position at the end of the electronic tube of the electrode 48 increases the difficulties in removing the heat generated by the electronic bombardment. In fact, this position at the end of the tube is generally used to place means making it possible to create a vacuum inside the electronic tube, a vacuum necessary for the establishment of the electron beam 12.
• To dissipate the heat generated at the level of the electrode 48 it is necessary to provide heat transfer to cooling means located in the immediate vicinity of the electrodes 40 and 44 on the side walls of the electronic tube.
• the invention aims to overcome this problem by directly using the means to create a vacuum in the electron tube to repel part of the electron beam 12 to the other electrodes 40 and 44 and not in the main direction of the materialized beam by axis 15 in Figure 1.
• an electronic tube comprising:
• a pumping pipe allowing to create a vacuum inside the tube, - an electron gun emitting an electron beam inside the tube,
• a collector directly collecting a first part of the electron beam, characterized in that the pumping rod directly repels a second part of the electron beam as director of the collector.
• the pumping pipe opens, inside the tube, along the axis of the electron beam. This simplifies the production of the end of the tube.
• FIG. 1 schematically shows the general operation of an electronic tube
• - Figure 2 shows an electronic tube using a single DC voltage source
• - Figure 3 shows an electronic tube using two sources of DC voltage
• - Figure 4 shows an electronic tube comprising 4 sources of DC voltage and a depressed collector
• FIG. 5 shows an end of the electronic tube with a depressed collector and a part of means for achieving the vacuum inside the tube. To simplify the rest of the description, the same elements will have the same references in the different figures.
• FIG. 5 partially represents an exemplary embodiment of an electronic tube implementing the invention.
• This tube comprises the tubular sheath 10 inside which the vacuum is provided by a pumping rod 50 whose one end 52, open, penetrates inside the sheath 10.
• the other end of the pumping rod is not shown in Figure 5 and is connected to a vacuum pump during the operations of manufacturing the electronic tube.
• the pump rod 50 is closed for example by pinching it until a hermetic cold welding of the walls of the pump rod.
• the electron tube comprises an electron gun 11 (not shown in the figure) emitting the electron beam 12 inside the tube and a collector 14 directly collecting a first part of the electron beam 12.
• the collector 14 comprises at minus one electrode. It has three electrodes 54, 56 and 58 in the example shown. The three electrodes 54, 56 and 58 are of revolution about the axis 15 along which the electron beam 12 mainly moves. Each electrode 54, 56 and 58 has a cylindrical part, respectively 60, 62 and 64, fixed inside the cylindrical sheath 10. The sheath 10 is also produced around the axis 15.
• the sheath 10 is for example made of ceramic and comprises metallized parts 66, 68 and 70 respectively receiving the electrodes 54, 56 and 58 .
• the electrodes are for example made from copper and their cylindrical parts 60, 62 and 64 are brazed respectively on the metallized parts 66, 68 and 70 of the sheath 10. Between these metallized parts, the sheath 10 has grooves 72 and 74 ensuring the insulation between the three electrodes 54, 56 and 58.
• the electrodes 54, 56 and 58 are all three each connected to a voltage source by means of connection means 76, 78 and 80 respectively.
• the three electrodes are pierced along the axis 15 of orifices, respectively 88, 90 and 92 allowing the electron beam 12 to pass at least in part.
• One end 81 of the sheath 10 is closed by a cover 82 mechanically connected to the sheath 10 with sufficient elasticity to collect any thermal stresses.
• This elastic connection between the sheath 10 and the cover 82 is for example provided by means of a collar 84.
• the cover 82 is of revolution around the axis 15. Its center is pierced so that the pumping rod 50 penetrates inside the electronic tube.
• the pumping pipe is electrically connected to a voltage source (not shown in the figure) by means of connection means 86. The voltage thus delivered to the pumping pipe 52 is close to that of the cathode 16 belonging to the barrel. electrons 11.
• the pumping rod 50 pushes directly, without intermediary, this part of the electron beam 12 in the direction of the collector 14 and more particularly towards the electrode 58.
• the pump rod 50 has the form of a tube whose end 52, located inside the electronic tube, is open. Indeed, the pumping rod 50 repels the part of the electron beam 12 arriving in its vicinity. It can remain open in the direction of the axis 15 because no (or very little) electron penetrates into the pump rod 50. There is therefore no risk of temperature rise of the pump rod 50 due to electronic bombardment.
• the end 52 of the pumping rod 50 has an asymmetrical shape with respect to the axis 15.
• This shape is for example obtained by bevelling the end 52.
• the bevel thus formed is a section of the end 52 by a plane not perpendicular to the axis 15.
• This asymmetrical shape allows the electrons arriving on the pumping rod 50 along the axis 15, to be pushed along an axis distinct from the axis 15 and thus reach one of the electrodes, in particular the electrode 58.
• the bevel cut of the end 52 is very simple to carry out, for example by cutting off the pumping rod 50.

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• Microwave Tubes (AREA)

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• 2001
  • 2001-12-14 FR FR0116242A patent/FR2833748B1/fr not_active Expired - Fee Related
• 2002
  • 2002-12-10 WO PCT/FR2002/004265 patent/WO2003054899A2/fr active Application Filing
  • 2002-12-10 US US10/498,792 patent/US6984940B2/en not_active Expired - Fee Related
  • 2002-12-10 EP EP02805362A patent/EP1466343B1/de not_active Expired - Lifetime

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