US2260851A - Electron lens for electric discharge tubes - Google Patents

Electron lens for electric discharge tubes Download PDF

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Publication number
US2260851A
US2260851A US216368A US21636838A US2260851A US 2260851 A US2260851 A US 2260851A US 216368 A US216368 A US 216368A US 21636838 A US21636838 A US 21636838A US 2260851 A US2260851 A US 2260851A
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Prior art keywords
lens
potential
electron
alternating
field
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US216368A
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English (en)
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Bruche Ernst
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General Electric Co
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General Electric Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • 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
    • H01J29/585—Arrangements for focusing or reflecting ray or beam in which the transit time of the electrons has to be taken into account

Definitions

  • the present invention relates to cathode ray tubes and more particularly toelectron lenses which control the direction of travel and focus of the electrons forming the beam.
  • charged particles may be given a velocity which is greater than that corresponding to-the amplitude of the alternating potential, The fact is thereby used that the particles in the system possess periods of motion which are of the same order asthe period of the alternating potential;
  • a particle. for which exists at a given instant an accelerating field in the'one field part anda retarding field in the other field part may
  • high-frequency alternating fields are used for the focusing efiects ofeleotronor ion lenses.
  • the lenses according to" the invention difier from-the known arrangements using electrical lenses operated by alternating potential in'that, with these, theperiod of the alternating potential is of the order of the time of motion of the electrons in the lens, while with theknown arrangements, where alternating potentials of. network frequency have been used, the period is only a fraction of the time of motion 'ofjthe v electrons from the position of the object 7 to the position of the picture.
  • FIG. 1 shows an immersion lens, which accord: ing to Fig. 1a consists of two co-axial hollow cylinders In, which have different potentials with respect to ground or. othe r fixed potential, The direction of the optical axis is indicated by 2-.
  • Figs. v1b,,and 1c illustrate for two different con-- ditions of operation the instantaneous variations of potential level which exist as one proceeds fromileft to right along the optical axis.
  • Fig.,1b I represents-such variation for a retarding lens systemand shows that the negative potential gent lens.
  • the symbol I placed above the axis a in 1b indicates that the lens effect of. the-potential field to the left of the central plane of thelens is such as to produce divergence'of the electron beam traversing the-lens.
  • The. symbol 0. placed above the axis a to the right of the lens center line indicates a converging effect of the lens system.
  • Fig. 1c the regions of'convergence and divergence are reversed. It will be seen from the. illustration, that in both lenses, i. e. the accelerating and the retarding lens, there are areas with divergent; effect-and areas with convergent effect. It will furthermore be seen that the divergent effect always appears in the area of highelectron.
  • the immersion lens are true quite 'generallyifor; anytypeof the short immersion or single lens. Only by using aperture stop lenses'it is possible to make divergent lenses. But also when using aperture stop lenses' .,it..is not possibleto make chromaticallycorrect'ed lens systems.
  • Fig. 1d represents the variation of the form of the potential field as a given electron prov gresses through the field,. the condition of the field being indicated for nine equally spaced po-. sitions of the electron.
  • Fig. 1e represents the continuous variation of the applied'alternating potential with electron position.
  • the electron in the area where the electron is that part of an immersion lens which corresponds to a divergent lens is formed.
  • the alternating potential obtains its maximum value, the electron is at the point III, so that now the most strongly curved potential curve 3 is formed.
  • the electron passes through the points IV and V, during which the field is decreased according to the curves 4 and 5.
  • the alternating potential has according to Fig. 1e reversed its sign and has thus changed the second part of the immersion lens into an accelerating part. While the electron moves from V to IX, this accelerating field is according to the curves 5 to 9 built up and then decreased. Also in the second part of the lens, the electron is then made subject to a divergent efiect.
  • the immersion lens By applying alternating potential, it is therefore possible to change the immersion lens into a pure divergent lens.
  • the phase of the alternating potential is shifted about 180, or the instant, at which the electron reaches the lens, is shifted about 180 of this potential, the immersion lens may be changed into a convergent lens of amplified effect.
  • the possibility of making a divergent lens is of special importance, since a divergent lens similar to the optical divergent lens was hitherto not known in electron-optics, so that it was also not possible to construct an achromatic lens arrangement.
  • Figs. 2 and 3 respectively represent as further cases a so-called single lens (Fig. 21:) consisting of three electrodes I2, 13 and I4 and an immersion objective lens (Fig. 3a") consisting of a cathode l5 and two cylinders 16 and Il.
  • Figs. 2b" and 3b" illustrate for these tWo cases the static potential field distribution at a given instant.
  • Figs. 2d and 3d respectively indicate the variations in field form which occur for the two constructions under consideration as a chosen electron proceeds through the lens space.
  • the signification of the potential is not the same as with static fields. It is more suitable in this case not to consider the concept of potential and to work with the effect of force.
  • U may, for example, be the potential, illustrated by Fig. lb or 10, of the immersion lens.
  • the lenses operated with alternating potential may, of course, be used just as well for positive particles as for electrons. In order to obtain the same effect, only the potentials in the lens electrodes have to be reversed with respect to the potentials selected for the electrons. Also, magnetic lenses may be operated in the same manner. It is of special advantage to use two coils connected in series. At a certain strength of the current flowing in the same direction in both coils, it may then be achieved that the picture rotation effected by the coils is so that the picture appears upright.
  • a sinusoidal potential or a sinusoidal current serves to operate the lenses. It is, of course, possible to use potentials of different Wave shape, such as rectangular or triangular, obtained in a wellknown manner.
  • the use of rectangular potentials or currents has the advantage that the maximum possible lens effect obtainable with a given field arrangement is achieved. If the immersion lens discussed in Fig. 1 were operated by a rectangular potential, the potential field would have the shape indicated at 3 in Fig. 1d while the electrons pass through the first part of the lens, and in the second part of the lens would have the shape illustrated by l. The same thing is true on using magnetic lenses, since also in this case, the whole refractive power of the first lens, and then the whole refractive power of the second lens, would become efiective.
  • one end of the envelope there is provided an manufacture of a chromatically corrected lens arrangement; since the convergent lens may be produced by a known static lens, while the divergent lens necessary for the correction is pro-.
  • alternating potential lens On using several lenses operated by alternating potential v or alternating current, it is suitable to use a single voltage or current source.
  • a single voltage or current source I In the leads to the single'lenses, devices may be provided which influence the phase of the potential or alter its shape. It is, for example, possible to use a potential source which produces a sinusoidal potential, and to operate only one of the lenses with this sinusoidal potential, while another lens, is operated by aid of a rectangular potential.
  • FIG. 4 there is illustrated diagrammatically a complete cathode ray tube apparatus for usefully app ing the invention.
  • This comprises an elongated envelope having a tubular shaft porelectron source comprising the combination of a cathode 23, a first accelerating electrode 24 and a second accelerating electrode 25, A battery 2! serves to impress an accelerating potential between the cathode 23 and the electrode 25.
  • a fluorescent screen on the wall surface 28, as is conventional in tubes of this character.
  • an electron lenssystem f the type illustrated in Fig. 3 hereof.
  • This comprises a first cylindrical electrode 30 which is arranged in partially telesco'ped' relation with a second, generally cylindrical electrode 3
  • the electrode may be connected to the source 33 which supplies potential to the lens system and may be energized thereby in such fashion that it permits electron current to flow only at intervals which are calculated to bring the electrons into the lens system in the proper phase relationship.
  • Known biasing means such as a battery 35 may be used to assist in the performance of this function.
  • the electrons which traverse the lens systern may be focused in a desired fashion upon the wall surface 28.
  • the apparatus may include magnetic or othermeans, illustrated dia- 1 grammatically at 31, for producing a cyclical deflection of the thus focused beam.
  • said lens system comprising a pair of mutually spaced apertured electrodes arranged'to be successively traversed by the beam, means for applying a potential between the electrodes and for periodically reversing such potential to produce an alternating lens field between said electrodes, and means for causing electronsto pass through said lens field only during periods whic include an instant of potential reversal.
  • the combination which includes 'means for producing a beam of electrons and an electron lens system which possesses utility mainly by virtue of its ability to control the lateral dimensions of the beam, said lens system comprising a pair of partially telescoped conducting cylinders arranged to be successively traversed by the beam, means for impressing a potential between the cylinders and for reversing such potential with a periodicity which is of the order of magnitude of the time taken by the electrons in passing through the lens system to produce an alternating lens field between said cylinders, and means for causing electrons to pass through said lens field only during periods which include an instant of po tential reversal, whereby electrons are subjected to the same directional effect throughout the entire region of influence of the lens system.
  • apparatus which includes means for producing an electron beam and in which it is neces sary for the proper functioning of the apparatus to exert a constant focusing effect on the various components of the beam
  • an electron lens system in the path of said beam for producing the said required focusing of the beam by exerting transverse refractive forces on the various components of the beam
  • a source of alternating potential for energizing the said lens system to provide an alternating lens field
  • the operating frequency of the said source being sufficiently high to assure thereversal of the potential in a period which is of the order of magnitude of the time taken by the electrons in passing through the lens field

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US216368A 1937-07-07 1938-06-28 Electron lens for electric discharge tubes Expired - Lifetime US2260851A (en)

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DE2260851X 1937-07-07

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2420514A (en) * 1944-05-25 1947-05-13 Gen Electric Electron lens structure
US2902622A (en) * 1956-04-23 1959-09-01 Int Standard Electric Corp Charged particle beam focusing system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2420514A (en) * 1944-05-25 1947-05-13 Gen Electric Electron lens structure
US2902622A (en) * 1956-04-23 1959-09-01 Int Standard Electric Corp Charged particle beam focusing system

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