US2294123A - Magnetic electron lens - Google Patents

Magnetic electron lens Download PDF

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Publication number
US2294123A
US2294123A US274038A US27403839A US2294123A US 2294123 A US2294123 A US 2294123A US 274038 A US274038 A US 274038A US 27403839 A US27403839 A US 27403839A US 2294123 A US2294123 A US 2294123A
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US
United States
Prior art keywords
shield
coil
magnetic
lens
electron
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Expired - Lifetime
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US274038A
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English (en)
Inventor
Miller Harold
Cairns John Edwin Ingliston
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
EMI Ltd
Electrical and Musical Industries Ltd
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EMI Ltd
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Filing date
Publication date
Application filed by EMI Ltd filed Critical EMI Ltd
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Publication of US2294123A publication Critical patent/US2294123A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/58—Arrangements for focusing or reflecting ray or beam
    • H01J29/64—Magnetic lenses
    • H01J29/66—Magnetic lenses using electromagnetic means only

Definitions

  • MAGNETIC ELEcTRoN LENS Filed May le, 1939 HAROLD JOHN EDWIN /NGL/STON CAIR/YS 2 Sheets-Sheet 2 INVENTORS M/LL ATTORNEY Patented Aug. 25, 1942 MAGNETIC ELECTRON LENS Harold Miller, Norwood Green, Southall, and John Edwin Ingliston Cairns, London, England, assignors to Electric & Musical Industries Limited, Hayes, Middlesex,
  • the present invention relates to magnetic and electron magnetic electron lenses.
  • the object of the present invention is to provide a further method of and devices for reducing the spread of the lens field along the axis of a magnetic electron lens.
  • a method of reducing the spread of the magnetic eld of a magnetic or electromagnetic lens device arranged to focus a, composite beam of electrons at a distance along the axis comprising arranging on the side of said device on which the spread of the i'ield is to be reduced, a substantially tubular magnetic shield in such manner as to provide a magnetic shunt for the field in the space on the side of said shield remote from said lens device.
  • an electron discharge device including a source of electrons arranged to emit of composite beam of electrons corresponding to a desired electron image or pattern and a magnetic or electromagnetic lens device adapted when energized to focus said beam at a surface, is provided, there being located in or about the path of said beam between said lens device and said surface a substantially tubular magnetic shield arranged in such manner as to provide a magnetic shunt for the field in the space between said shield and said surface to reduce the strength of the field due to said lens devce
  • said shield is of substantially frustroconical form and is arranged with its larger end adjacent said lens device and its narrower end presented towards said surface, though if desired the direction of the shield can be reversed.
  • the smaller end of the shield is preferably provided with means providing a low reluctance path or paths into said shield, said path or paths extending substantially perpendicularly to the path of said beam.
  • Fig. 3 shows a section of a preferred form of the invention as included in a television signal transmitting tube.
  • the lens coil C is shown arranged about an axis A and is provided with the usual high permeability shield B surrounding the coil on the outside only, the inside of the coil being unshielded.
  • the provision of the shield B tends to confine the eld generated by the coil C to the region between the planes of the ends of the coil,
  • the provision of the shield B is not in itself suicient to eliminate completely the spread of magnetic ux along the axis A, and thus in accordance with the invention a further high permeabiilty shield S is provided consisting in the case shown of a frustro-conical member which may be formed of thin sheet iron of high permeability arranged co-axially with the coil C, the smallest diameter d of the shield being substantially equal to the internal diameter of the coil.
  • a greater reduction in the strength of the field can be obtained by using the shield having a surface which approximates closely to that formed by the revolution of a line of force due to the coil about the axis.
  • a surface is represented, for example at F from which it will be seen that in this case the shield S will be flared and have a form somewhat resembling that of the mouth of a trumpet.
  • the shield can be made cylindrical, the diameter of the shield being substantially equal to that of the diameter of the coil C or the shield can be reversed as illustrated in Fig. 2.
  • the reduction in the iield strength obtained is not so great from the coil up to the point P in the neighborhood of the smaller end of the shield, but beyond this point the reduction of field strength produced by the coil is greater than in the case shown in Fig. l, and in general the arrangement of Fig. 2 is preferred over that shown in Fig. 1.
  • shields such as S in Figs. l and 2 can be provided on each side of the coil C.
  • the additional shield or shields provided in accordance with the invention is or are preferably made of a material having a high permeability at field strengths of the order, say, up to 16 gauss,
  • the shield can be formed of pure annealed iron though the high permeability alloys are preferred.
  • the thickness of the shield is preferably of the order of a few millimetres.
  • the tube therein shown comprises a bulb I Within which is mounted a mosaic electrode 2Y in such a position as to be scanned by a scanning beam projected from an electron gun mounted in an extension iv of the bulb.
  • the electrode 2 also receiving a composite beam of electrons emitted from a photo-cathode 5 mounted in a further extension 6 of the bulb.
  • the composite beam of electrons from cathode 5 is focussed on the mosaic 2 by means of a magnetic lens coil 1, which, in the preferred arrangement, is mounted on a copper former 8 and is formed in two parts through which energizing currents flow in opposite directions in the manner described by Bruche in Zeitschrift fur Technische Physik, 1936, page 588.
  • An image of the subject to be televised is projected on the cathode 5- by means of the optical system 9.
  • the mode of operation of the parts in Fig. 3 so far referred to is well understood in the art and will not be further described in detail.
  • the lens coil 'I operates to produce an intense iield in its own neighborhood and the double coil arrangement results in a reduction of the field spread along the axis of the coil.
  • the arrangement can, according to the invention, be further improved by the provision in association with the lens coil l, of a substantially frusto-conical shield I0.
  • This shield is formed of highly permeable magnetic material, for example, radio metal.
  • the shield I0 is generally frusto-conical in form and is formed in two parts II and I2 which are arranged to telescope one within the other as indicated at I3, the part II, which has the larger diameter, providing a housing for the lens coil 1 and the part I2 fitting closely round the constricted portion I4 of the extension 6 of the bulb I.
  • the telescopic arrangement of the parts II and I2 of the shield il) facilitates the adjustment of the position of coil 1 with respect to cathode 5 whilst maintaining continuity of shielding.
  • the narrow or constricted end I5 of shield ID is preferably provided with a ring I6 formed of annular laminations of magnetic material fitting closely on the portion I4 of aforesaid extension 6.
  • This ring I6 affords a low reluctance path for ux which would otherwise pass axially of the extension to the vicinity of the mosaic electrode 2, the flux entering the ring I6 being returned through the shield I0 around the coil 1.
  • the provision of the ring I6, while it is found to increase the spiral distortion of the electron image produced on the mosaic electrode 2 is found to produce such a reduction in the field due to coil 'I at the electrode 2, that the slight disadvantage produced is wholly outweighed.V
  • a substantially frustroconical shield IIJ arranged with its narrow end remote from the lens coil 1 provides an arrangement of which the eicacy is in no way interfered with by the necessity of accommodating the extension 4 of the tube wherein the scanning beam is generated. Moreover ample space can be provided outside the shield I0, in which space scanning coils, indicated at I'I, can be arranged.
  • means such as the ring I6 affording a low reluctance path or paths into Ythe shield I! might be provided on the smaller end of the shield S of Fig. l.
  • An electron lens arrangement for focusing a composite group of electrons comprising coil means for focusing said composite group and a member having a high magnetic permeability positioned externally to and immediately adjacent said coil means for intercepting a portion of the ux from said coil means, whereby said ux may be intercepted substantially normal to said member, said member having a frustro-conical shape.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US274038A 1938-06-28 1939-05-16 Magnetic electron lens Expired - Lifetime US2294123A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB19093/38A GB516478A (en) 1938-06-28 1938-06-28 Improvements in or relating to magnetic electron lenses

Publications (1)

Publication Number Publication Date
US2294123A true US2294123A (en) 1942-08-25

Family

ID=10123665

Family Applications (1)

Application Number Title Priority Date Filing Date
US274038A Expired - Lifetime US2294123A (en) 1938-06-28 1939-05-16 Magnetic electron lens

Country Status (5)

Country Link
US (1) US2294123A (fr)
CA (1) CA432539A (fr)
DE (1) DE754660C (fr)
FR (1) FR855209A (fr)
GB (1) GB516478A (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2469165A (en) * 1946-10-29 1949-05-03 Rca Corp Correction device for electron lenses
US2572644A (en) * 1947-08-29 1951-10-23 Emi Ltd Electron discharge tube
US2892962A (en) * 1955-10-07 1959-06-30 Karl F Ross Electronic lens system
US3163794A (en) * 1960-06-20 1964-12-29 Philco Corp Deflection yoke with separable portions for crt with constricted neck
US3165677A (en) * 1960-08-30 1965-01-12 Gen Instrument Corp Television tube deflection coil assembly with separable yoke sections

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB462683A (en) * 1935-09-12 1937-03-12 Alfred Henry Gilbert Improvements in or relating to methods of mounting deflecting and focussing means for cathode-ray tubes and the like

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2469165A (en) * 1946-10-29 1949-05-03 Rca Corp Correction device for electron lenses
US2572644A (en) * 1947-08-29 1951-10-23 Emi Ltd Electron discharge tube
US2892962A (en) * 1955-10-07 1959-06-30 Karl F Ross Electronic lens system
US3163794A (en) * 1960-06-20 1964-12-29 Philco Corp Deflection yoke with separable portions for crt with constricted neck
US3165677A (en) * 1960-08-30 1965-01-12 Gen Instrument Corp Television tube deflection coil assembly with separable yoke sections

Also Published As

Publication number Publication date
DE754660C (de) 1953-03-09
CA432539A (fr) 1946-01-15
GB516478A (en) 1940-01-03
FR855209A (fr) 1940-05-06

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