US2799813A - Magnetic electron lens - Google Patents

Magnetic electron lens Download PDF

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Publication number
US2799813A
US2799813A US492542A US49254255A US2799813A US 2799813 A US2799813 A US 2799813A US 492542 A US492542 A US 492542A US 49254255 A US49254255 A US 49254255A US 2799813 A US2799813 A US 2799813A
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US
United States
Prior art keywords
rings
magnetic
electron lens
lens
magnet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US492542A
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English (en)
Inventor
Rademakers Adriaan
Haes Eduard Johan
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.)
US Philips Corp
North American Philips Co Inc
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US Philips Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by US Philips Corp filed Critical US Philips Corp
Application granted granted Critical
Publication of US2799813A publication Critical patent/US2799813A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0273—Magnetic circuits with PM for magnetic field generation
    • H01F7/0278—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles
    • 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
    • H01J29/68—Magnetic lenses using permanent magnets only

Definitions

  • the invention relates to a magnetic electron lens comprising two opposite circular rings of permanent magnetic material.
  • a known embodiment of such electron lenses has the rings arranged such that their direction of magnetisation extends radially or else axially relative to the axis of the rings.
  • the first-mentioned method of magnetisation has the disadvantage that the stray field on the axis beyond the magnets is larger than with the last-mentioned method of magnetisation, though it has the advantage that a smaller quantity of magnetic material is re quired to obtain the same lens intensity.
  • the invention has for its object to provide an electron lens in which the magnet rings are magnetized in a manner such that even a smaller quantity of magnetic material is required. It is characterized in that the inner cylindrical surface of one ring constitutes a pole surface having south magnetism and that of the other ring constitutes a pole surface having north magnetism, whereas the two surfaces of the rings facing one another constitute the pole surfaces of opposite magnetism.
  • Fig. 1 shows a magnetic electron lens according to the invention
  • Fig. 2 shows graphs to explain Fig. 1;
  • Fig. 3 shows a variant of the embodiment shown in Fig. 1;
  • Fig. 4 shows a polarisation device for the magnets shown in Fig. 1;
  • Fig. 5 shows a magnetic electron lens comprising means to compensate the temperature dependence of the lens intensity
  • Fig. 6 shows, in cross-section, a modification of the device illustrated in Fig. 5.
  • Fig. 1 shows a magnetic electron lens comprising two opposite circular rings 1 and 2 of permanent magnetic material, for example a ceramic ferromagnetic material composed of iron oxide and an oxide of barium, strontium or lead and having a hexagonal crystal structure, which may for example be applied around the neck of a cathode-ray tube.
  • permanent magnetic material for example a ceramic ferromagnetic material composed of iron oxide and an oxide of barium, strontium or lead and having a hexagonal crystal structure, which may for example be applied around the neck of a cathode-ray tube.
  • the rings in this case have a magnetisation I, wherein the inner cylindrical surface 3 of the ring 1 constitutes a pole surface having south magnetism, the inner cylindrical surface 4 of the ring 2, on the contrary, constitutes a pole surface having north magnetism, whereas the two opposite surfaces 5 and 6 of the rings 1 and 2 respectively constitute pole surfaces of opposite magnetism, i. e., northand south-magnetism respectively.
  • the curves illustrate the magnitude of the magnetic field strength H, measured along the optical axis 7 of the lens illustrated in Fig. l with two different values (0 and 8 millimeters) of the distance 1 between the two rings 1 and 2, the curves r relating to the case in which the rings are magnetized radially in accordance with the known embodiment, whereas the curves s relate to the case in which they are magnetized in accordance with the invention.
  • the said economy in material is found to be of particular importance, if the axial thickness d differs little from the radial thickness h of the rings; their ratio lies preferably between the values 2/3 and 3/2, in which case at least 20% of the permanent magnet material may be economized. Moreover, it is found that the material in the proximity of the corners or edges 9 and 1t), remote from the pole surfaces 3, 5 and 5, 6 respectively, contributes to a smaller extent to the field H on the axis 7 than the further material. Fig. 3 shows therefore an embodiment, wherein these corners are bevelled, which provides a further economy of material of another 20%.
  • Fig. 4 shows a polarisation device for producing the magnetisation I of Fig. 1. It comprises two co-axial magnet coils 13 and 14, between which the magnet 1 to be polarized is arranged and which, for example by inverting the sense of winding and/or by a different choice of the number of turns, produce rotational-symmetrical fields of different values in the space between the two coils, of which the resultant Hp lies obliquely to the axis 7 of the coils, and which resultant produces, consequently, the desired magnetisation I in the magnet 1.
  • the lens intensity of the electron lenses shown in Figs. 1 and 3 is found to drop, in general, with temperature, since the field produced by the magnet rings 1 and 2 drops, as a rule, with increasing temperature.
  • This drop in lens intensity may be compensated, according to Fig. 5, by means of a spring 17, which keeps the rings 1 and 2 spaced apart and of which the rigidity has a prescribed value, which is chosen such that the magnets 1 and 2 are spaced apart by a desired, predetermined distance, dependent upon the lens intensity desired along the axis.
  • the spring 17 is adjusted to provide an expansion force tending to separate the magnets 1 and 2, to offset the magnetic attractive forces tending to bring the magnets 1 and 2 together.
  • a spring 22 is arranged, preferably, as a push spring or a tensile spring, between the magnet ring 1 and a member 21 at some distance from the fixed magnet ring 2', this member 21 being stationary.
  • the magnet 1 is mounted on a support 20, which is axially displaceable.
  • the position of the magnet 1' which determines the lens intensity, depends on the force imparted by the spring 22 and the strength of the attractive magnetic force be tween the magnets 1' and 2.
  • the said compensation method may even be carried out, if the rings 1 and 2 are magnetized in a radial direction, i. e. in general, if the rings 1 and 2 attract one another.
  • a magnetic electron lens comprising a pair of substantially fiat, coaxial, adjacent, annular, permanent magnet members, each of said annular members having a given thickness in an axial direction and a given thickness in a radial direction between its inner and outersurfaces, one of said members being magnetized obliquely forming a south pole on its inner surface and a north pole on the substantially flat surface thereof facing said other member, the other member being magnetized obliquely forming a north pole on its inner surface and a south pole on the substantially fiat surface thereof facing said one member, said pair of members cooperating to produce a magnetic field substantially along the axis thereof.
  • a magnetic electron lens as claimed in claim 1 wherein the edges of the annular members remote from their facing surfaces and their axis are bevelled.
  • a magnetic electron lens comprising a pair of substantially flat, coaxial, spaced, annular, permanent magnet members, said magnet members being magnetized to produce opposite polarity poles on facing surfaces thereof thereby producing attractive forces therebetween, said members producing magnetic fields whose magnitude is temperature dependent, and resilient means for maintaining said members spaced apart, said resilient means producing an expansion force at least partly counteracting the attractive forces between the magnets.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Magnetic Treatment Devices (AREA)
US492542A 1954-03-05 1955-03-07 Magnetic electron lens Expired - Lifetime US2799813A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL766857X 1954-03-05

Publications (1)

Publication Number Publication Date
US2799813A true US2799813A (en) 1957-07-16

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ID=19827648

Family Applications (1)

Application Number Title Priority Date Filing Date
US492542A Expired - Lifetime US2799813A (en) 1954-03-05 1955-03-07 Magnetic electron lens

Country Status (5)

Country Link
US (1) US2799813A (en, 2012)
DE (1) DE1035812B (en, 2012)
FR (1) FR1120026A (en, 2012)
GB (1) GB766857A (en, 2012)
NL (1) NL87140C (en, 2012)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2849636A (en) * 1952-01-04 1958-08-26 Philips Corp Magnetic electron lens
US2888634A (en) * 1957-07-09 1959-05-26 Du Mont Allen B Lab Inc Electric circuit
US2943219A (en) * 1955-09-19 1960-06-28 Philco Corp Beam positioning apparatus for cathode ray tubes
US4647887A (en) * 1984-12-24 1987-03-03 The United States Of America As Represented By The Secretary Of The Army Lightweight cladding for magnetic circuits
US5014028A (en) * 1990-04-25 1991-05-07 The United States Of America As Represented By The Secretary Of The Army Triangular section permanent magnetic structure

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL7812540A (nl) * 1978-12-27 1980-07-01 Philips Nv Kathodestraalbuis.

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2157182A (en) * 1935-12-31 1939-05-09 Rca Corp Cathode ray deflecting device
US2339087A (en) * 1939-06-30 1944-01-11 Milwaukee Gas Specialty Co Thermostatic control device
US2525919A (en) * 1948-07-01 1950-10-17 Hazeltine Research Inc Centering arrangement for cathode-ray tubes

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2157182A (en) * 1935-12-31 1939-05-09 Rca Corp Cathode ray deflecting device
US2339087A (en) * 1939-06-30 1944-01-11 Milwaukee Gas Specialty Co Thermostatic control device
US2525919A (en) * 1948-07-01 1950-10-17 Hazeltine Research Inc Centering arrangement for cathode-ray tubes

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2849636A (en) * 1952-01-04 1958-08-26 Philips Corp Magnetic electron lens
US2943219A (en) * 1955-09-19 1960-06-28 Philco Corp Beam positioning apparatus for cathode ray tubes
US2888634A (en) * 1957-07-09 1959-05-26 Du Mont Allen B Lab Inc Electric circuit
US4647887A (en) * 1984-12-24 1987-03-03 The United States Of America As Represented By The Secretary Of The Army Lightweight cladding for magnetic circuits
US5014028A (en) * 1990-04-25 1991-05-07 The United States Of America As Represented By The Secretary Of The Army Triangular section permanent magnetic structure

Also Published As

Publication number Publication date
GB766857A (en) 1957-01-23
FR1120026A (fr) 1956-06-28
DE1035812B (de) 1958-08-07
NL87140C (en, 2012)

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