US3401295A - Periodic permanent magnet focusing system for electron discharge devices - Google Patents

Periodic permanent magnet focusing system for electron discharge devices Download PDF

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Publication number
US3401295A
US3401295A US551076A US55107666A US3401295A US 3401295 A US3401295 A US 3401295A US 551076 A US551076 A US 551076A US 55107666 A US55107666 A US 55107666A US 3401295 A US3401295 A US 3401295A
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Prior art keywords
permanent magnet
periodic
magnetic
magnets
electron
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Expired - Lifetime
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US551076A
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English (en)
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Suzuki Yoshihisa
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Hitachi Ltd
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Hitachi Ltd
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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
    • H01J23/02—Electrodes; Magnetic control means; Screens
    • H01J23/08—Focusing arrangements, e.g. for concentrating stream of electrons, for preventing spreading of stream
    • H01J23/087—Magnetic focusing arrangements
    • H01J23/0873—Magnetic focusing arrangements with at least one axial-field reversal along the interaction space, e.g. P.P.M. focusing

Definitions

  • This invention relates to electron tubes with a beam focusing system of the type using periodic permanent magnets and more particularly to an electron tube of the kind described which has such a structure that the permanent magnets for the electron beam focusing can be magnetized after they have been mounted in place in the electron tube and the electron tube has been subsequently evacuated.
  • FIG. 1 is a sectional view showing the structure of prior art electron tubes with a beam focusing system of the type using conventional periodic permanent magnets;
  • FIG. 2 is a schematic sectional view showing the structure of a periodic permanent'magnet device forming the electron beam focusing system in a prior art electron tube of the kind described;
  • FIG. 3 is a schematic sectional view showing the structure of a permanent magnet device forming the electron beam focusing system in one embodiment according to the invention.
  • FIG. 4 is a schematic sectional view showing the structure of a permanent magnet device forming'the electron beam focusing system in another embodiment according to the invention.
  • Periodic permanent magnet devices are frequently fa vored for use in electron tubes such as traveling wave tubes and backward wave tubes for the focusing of an electron beam of high electron current density owing to the advantage that these devices are small in size and light in weight.
  • a typical construction of the prior art electron tubes having such a device therein is shown in section in FIG. 1 by way of example.
  • the electron tube shown in FIG. 1 is shown in section in FIG. 1 by way of example.
  • the prior electron tube having the structure as shown in FIG. 1 its beam focusing system generally has such an arrangement that cylindrical permanent magnets of inverse polarity are alternately disposed in coaxial relation with each other.
  • the magnetic electron beam focusing system in the prior electron tube has, for example, a periodic structure as shown in FIG. 2.
  • This magnetic electron beam focusing system comprises a plurality of cylindrical permanent magnets 6 and a plurality of cylindrical permanent magnets '6 magnetized in a direction opposite to that of the permanent magnets 6.
  • These permanent magnets 6 and 6 of inverse polarity are alternately and coaxially disposed along the central axis and a magnetic pole piece 7 having an electron beam passage '8 therein is interposed between each pair of the permanent magnets 6 and 6 of inverse polarity so that a periodic magnetic field can be established about the central axis. Since the permanent magnets which have already been magnetized in opposite directions to each other are assembled to form the above-described known type of magnetic electron beam focusing system, it is impossible to magnetize these masses of permanent magnet material in opposite directions to each other after mounting the non-magnetized masses of permanent magnet material in place.
  • the inventors have previously proposed a periodic permanent magnet device in which masses of permanent magnet material can be magnetized after being mounted in place and after the step of subsequent evacuation.
  • This periodic permanent magnet device had such a structure that non-magnetized cylindrical masses of permanent magnet material are mounted in a suitably spaced relation from each other and are magnetized in the same direction after the step of evacuation.
  • the periodic permanent magnet device of the kind described has had some drawbacks in that the diameter of magnetic shielding plates at opposite ends thereof must-be made extremely larger than that of the cylinder type permanent magnets in order to obtain a periodic magnetic field of good periodicity and of constant peak value over the extremely large length.
  • This kind of periodic permanent magnet device has thus been defective in that the size and dimensions of electron tubes become quite large. 7
  • the present invention provides a novel and improved periodic permanent magnet device for incorporation in an electron tube of the kind specified.
  • hollow cylindrical magnets are each split into halves at the middle portion thereof and an annular magnetic pole piece having an outside diameter larger than the outside diameter of the above hollow cylindrical magnet is interposed between the halfsplit magnet sections so as to restrict the path length of the magnetic flux through the outer space of the hollow cylindrical magnets.
  • the magnetic field at the inner side of the periodic permanent magnet device is not appreciably affected by this interposition of magnetic pole pieces and such influence becomes almost negligible by arranging the magnets and pole pieces in such a manner that the inside diameter of the magnetic pole piece is slightly greater than the inside diameter of the hollow cylindrical magnet.
  • FIG. 3 shows the sectional structure and magnetic field distribution for a magnetic electron beam focusing means in one embodiment of the electron tube according to the invention.
  • the magnetic electron beam focusing means comprises spaced pairs of hollow cylindrical permanent magnets 1 and 2 which are magnetized in the same direction, each forming a unit permanent magnet.
  • the magnetic flux inside the hollow cylindrical magnets passes through the same passage as in the previously described case, but the magnetic flux appearing across the gap between the pairs of hollow cylindrical magnets passes through the hollow cylindrical magnets on opposite sides of the gap, then through the magnetic pole piece 5 and through the outer space of the hollow cylindrical magnets to form a closed loop.
  • the provision of the magnetic pole pieces 5 is so effective for greatly restricting the passage of magnetic flux through the outer space that the periodicity or symmetry of the periodic magnetic field would not be impaired at all, even if the permanent magnet device is so constructed as to have a great length.
  • FIG. 4 shows the sectional structure of a magnetic electron beam focusing means employed in another embodiment according to the invention, in which like ref erence numerals appearing in FIG. 3 are used to denote like parts.
  • the arrangement shown in FIG. 4 differs from that shown in FIG. 3 in that a hollow cylindrical magnet 1' having no magnetic pole piece 5 for the restriction of the path length of magnetic flux through the outer space of the hollow cylindrical magnets is disposed between annular magnetic pole pieces 3 and 4 and between pairs of hollow cylindrical magnets 1 and 2. It will thus be ap preciated that the magnetic pole piece 5 need not be interposed in every pair of hollow cylindrical magnets and may be disposed in a suitably spaced relation.
  • the inventive arrangement in which a magnetic pole piece 5 is interposed between the halved sections of a hollow cylindrical permanent magnet is quite effective in restricting the path length of magnetic flux through the outer space of the hollow cylindrical permanent magnet for thereby providing a periodic magnetic field of good periodicity and of constant peak value.
  • the size of the electron tube can be made quite small because the good periodic magnetic field is used for beam focusing, even if it is quite long, and because there is no need of providing magnetic shielding plates of large diameter on opposite ends of periodic permanent magnet devices such as are employed in prior electron tubes of this type.
  • an electron discharge device having electron beam generating means for emitting an electron beam along a prescribed path, a collector for collecting the electron beam emitted from said electron source and a periodic magnetic focusing system provided between said source and said collector surrounding at least a portion of the path of said electron beam progressing therebetween for focusing said electron beam
  • said focusing system comprising: a permanent magnet assembly formed of a plurality of unit permanent magnets of hollow cylindrical shape coaxially disposed in spaced relation with their direction of magnetization aligned in one direction, at least one of said unit permanent magnets being formed of a pair of adjacent half-sections confronting each other in a plane perpendicular to the beam path; and at least one annular magnetic pole piece coaxially interposed between said half-sections of said one unit permanent magnet and having an outside diameter larger than that of said one unit permanent magnet whereby reducing the length of magnetic path formed through the outer space of said permanent magnet assembly.

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US551076A 1965-05-21 1966-05-18 Periodic permanent magnet focusing system for electron discharge devices Expired - Lifetime US3401295A (en)

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JP2962465 1965-05-21

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1791080B1 (de) * 1968-09-07 1970-09-16 Philips Patentverwaltung Permanentmagnetische fokussierungsanordnung fuer ei n mehr klammerklystron
DE3125977A1 (de) * 1980-07-02 1982-03-04 Hitachi, Ltd., Tokyo Elektromagnetfokussier-kathodenstrahlroehre
US4404494A (en) * 1980-04-21 1983-09-13 Siemens Aktiengesellschaft Travelling wave tube with periodic-permanent magnet focusing system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3013172A (en) * 1958-02-25 1961-12-12 Nippon Electric Co Electron beam converging device
US3142008A (en) * 1960-03-18 1964-07-21 Gen Precision Inc Temperature compensation element for a traveling wave tube periodic array
US3334264A (en) * 1963-07-01 1967-08-01 Gen Electric Beam focusing magnet system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3013172A (en) * 1958-02-25 1961-12-12 Nippon Electric Co Electron beam converging device
US3142008A (en) * 1960-03-18 1964-07-21 Gen Precision Inc Temperature compensation element for a traveling wave tube periodic array
US3334264A (en) * 1963-07-01 1967-08-01 Gen Electric Beam focusing magnet system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1791080B1 (de) * 1968-09-07 1970-09-16 Philips Patentverwaltung Permanentmagnetische fokussierungsanordnung fuer ei n mehr klammerklystron
US4404494A (en) * 1980-04-21 1983-09-13 Siemens Aktiengesellschaft Travelling wave tube with periodic-permanent magnet focusing system
DE3125977A1 (de) * 1980-07-02 1982-03-04 Hitachi, Ltd., Tokyo Elektromagnetfokussier-kathodenstrahlroehre

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Publication number Publication date
NL144431B (nl) 1974-12-16
NL6606959A (en)) 1966-11-22

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