US3013172A - Electron beam converging device - Google Patents

Electron beam converging device Download PDF

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Publication number
US3013172A
US3013172A US789846A US78984659A US3013172A US 3013172 A US3013172 A US 3013172A US 789846 A US789846 A US 789846A US 78984659 A US78984659 A US 78984659A US 3013172 A US3013172 A US 3013172A
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Prior art keywords
magnetic
electron beam
magnets
units
converging device
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Expired - Lifetime
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US789846A
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English (en)
Inventor
Ito Michiaki
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NEC Corp
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Nippon Electric Co 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 a beam focussing device which makes use of periodically varying magnetic iiux as the converging means for the electron beam.
  • a beam focussing device which makes use of periodically varying magnetic iiux as the converging means for the electron beam.
  • it relates to an electron beam converging device used in microwave beam tubes, particularly traveling wave tubes.
  • Electron beam converging devices previously proposed attempt to provide a magnetic flux along the axis of the beam which varies in strength substantially as a sine wave. This is done by arranging ring shaped magnets in opposition, that is with the like poles adjacent one another. Generally, also, there are provided magnetic pole pieces between the adjacent magnets to bring the magnetic field effects down closer to the tube carrying the electron beam. In such arrangements it is necessary to provide for coupling an external circuit to the slow wave structure within the tube. This is generally done by waveguides which extend at right angles to the tube. These waveguides then introduce a gap in the magnetic structure and so disturb the continuity of the magnetic field introducing certain distortion.
  • a magnetic beam focussing device made up of a plurality of magnetic units, each of these units includes two magnets with adjacent poles of opposite polarity separated by a region of high magnetic reluctance. These units are assembled with adjacent poles of opposite po-l larity facing one another. Preferably, also magnetic pole pieces are interposed between adjacent magnetic units.
  • FIG. la is a Sectio-nal diagrammatic representation of a magnetic focussing unit of the prior art
  • tFIG. 1b is a curve illustrating the variation in magnetic ux along the axis of the beam in FIG. la;
  • FIG. 2 is a diagram illustrating the type of disturbances which may be introduced by the structure of FIG. la;
  • FIG. 3a is a view, particularly in cross section, illustrating an embodiment of the present invention.
  • FIG. 3b is a curve showing the variation in magnetic flux along the beam axis obtained with the structure shown in FIG. 3a.
  • FIG. la there is shown a magnetic l focussing assembly comprising a plurality of magnets 1 in the form of rings. These magnets are positioned with adjacent pole faces of like polarity. Intermediate each of the magnets are provided pole pieces of magnetic material 2. The electron beam 3 of tube 4 is shown traversing the axis of the magnet assembly. Waveguides for coupling to the external circuits are shown at 5.
  • FIG. 2 the nature of the disturbance for the beam can be better understood.
  • the beam penetrating factor of the magnetic field is plotted as ordinates and the operating voltage for the electron beam as abscissa.
  • the operating voltage for the electron beam is maintained.
  • a stable penetrating factor is obtained as shown by curve 6.
  • the penetrating factor increases smoothly to nearly penetration beyond the area 7, which illustrates the lower limiting voltage for operation of the beam tube.
  • the waveguides 5 there is produced an excessive variation in the penetration factor with the changes in operating tube voltage as illustrated in the curve 8L
  • These disturbing effects are undesirable.
  • Methods of reducing or avoiding these eects have been proposed by the addition of other magnetic devices external of the waveguide 5. These additional structures, however, are difficult to construct and are quite critical, requiring extreme care in accurately adjusting them.
  • FIG. 3a An example of this new structure is illustrated in FIG. 3a.
  • individual magnetic units composed of separate permanent magnets 1 and 1" separated by a spacing of high magnetic reluctance 9.
  • This spacer may preferably be in the formy of some non-magnetic material in the interest of the construction of a unitary assembly.
  • Magnets 1 and 1" are arranged in magnetic aiding relation. That is, with adjacent poles being of opposite polarity. It will, therefore, be apparent that at each end of these units there will be poles of opposite polarity..
  • a plurality of these units are then assembled with poles of opposite polarity on the separate units, adjacent one another.
  • Intermediate these units are provided magnetic pole pieces 2 preferably made of soft iron or some such material.
  • the permanent magnets may be made of some high magnet steels, although in the preferred construction some of the permanent magnet type of ferrites are used.
  • the magnetic field in the axis of the assembly will not be a pure sine wave but will have ripples at the peaks of the waves producing a field along these axes corresponding to a sine wave variation with a superimposed third harmonic as shown in FIG. 3a by curve 10.
  • the magnetic flux density B2 in the form shown by selection of the desired magnetic material, controlling the dimension ratio of the magnets and the spacing, and adjusting the inner diameters of the pole pieces.
  • the magnetic flux B2 can then be represented by the following equation:
  • B2 cos @L- eos S22-Z
  • L is the length of the magnetic unit including elements 1', 1" and 9, and Z is the magnetic strength of the field at the axis. It has been found that a field closely following this equation may be determined theoreti/:ally or experimentally, having in mind the various parameters of the elements forming the assembly.
  • magnets 1' and 1" may be made of permanent magnet ferrites with an outside diameter of 0.89 L, an inside diameter of 0.27 L, and a space of 0.18 L. Such a structure has been found to obtain a flux distribution substantially as described above.
  • the spacing by the elements 1 and 1" may be so chosen that the waveguide width is substantially the same as this spacing.
  • the waveguide couplers may then be inserted between two magnets of a single unit in place of the normal spacers 9.
  • Vpair of magnets are each in the form of a hollow cylinder.
  • a beam focussing device further comprising electrical wave transmitting devices extending from Athe external surface of one of said units into the hollow of the cylinder defined by said unit through said fixed region.

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US789846A 1958-02-25 1959-01-29 Electron beam converging device Expired - Lifetime US3013172A (en)

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JP3013172X 1958-02-25

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3401295A (en) * 1965-05-21 1968-09-10 Hitachi Ltd Periodic permanent magnet focusing system for electron discharge devices
DE3014404A1 (de) * 1979-04-11 1980-10-16 Nippon Electric Co Wanderfeldroehre

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2797360A (en) * 1953-03-26 1957-06-25 Int Standard Electric Corp Travelling wave amplifiers
US2812470A (en) * 1954-10-22 1957-11-05 Bell Telephone Labor Inc Periodic focusing in traveling wave tubes
US2843775A (en) * 1955-06-28 1958-07-15 Int Standard Electric Corp Electron tube magnetic focusing device
US2847607A (en) * 1953-04-29 1958-08-12 Bell Telephone Labor Inc Magnetic focusing system
US2863086A (en) * 1954-02-09 1958-12-02 Bell Telephone Labor Inc Traveling wave tube
US2867744A (en) * 1953-09-30 1959-01-06 Bell Telephone Labor Inc Traveling wave tube
US2867745A (en) * 1953-10-07 1959-01-06 Bell Telephone Labor Inc Periodic magnetic focusing system

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2797360A (en) * 1953-03-26 1957-06-25 Int Standard Electric Corp Travelling wave amplifiers
US2847607A (en) * 1953-04-29 1958-08-12 Bell Telephone Labor Inc Magnetic focusing system
US2867744A (en) * 1953-09-30 1959-01-06 Bell Telephone Labor Inc Traveling wave tube
US2867745A (en) * 1953-10-07 1959-01-06 Bell Telephone Labor Inc Periodic magnetic focusing system
US2863086A (en) * 1954-02-09 1958-12-02 Bell Telephone Labor Inc Traveling wave tube
US2812470A (en) * 1954-10-22 1957-11-05 Bell Telephone Labor Inc Periodic focusing in traveling wave tubes
US2843775A (en) * 1955-06-28 1958-07-15 Int Standard Electric Corp Electron tube magnetic focusing device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3401295A (en) * 1965-05-21 1968-09-10 Hitachi Ltd Periodic permanent magnet focusing system for electron discharge devices
DE3014404A1 (de) * 1979-04-11 1980-10-16 Nippon Electric Co Wanderfeldroehre

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NL236247A (en))

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