US2965782A - Magnetic focusing systems for travelling wave tubes - Google Patents

Magnetic focusing systems for travelling wave tubes Download PDF

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Publication number
US2965782A
US2965782A US798212A US79821259A US2965782A US 2965782 A US2965782 A US 2965782A US 798212 A US798212 A US 798212A US 79821259 A US79821259 A US 79821259A US 2965782 A US2965782 A US 2965782A
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Prior art keywords
region
tube
delay line
pole pieces
over
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Expired - Lifetime
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US798212A
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English (en)
Inventor
Weaver Francis James
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Teledyne UK Ltd
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English Electric Valve 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

  • FENEN'roRZ BIO/W020 (9W Um W02 i: A'r'roRrNEn MAGNETIC FOCUSING SYSTEMS FOR TRAVEL- LING WAVE TUBES Francis James Weaver, Great Baddow, England, assignor to English Electric Valve Company Limited, London, England, a British company Filed Mar. 9, 1959, Ser. No. 798,212
  • This invention relates to magnetic focusing systems for travelling wave tubes and more specifically to magnetic focusing systems of the kind including so-called periodic magnetic field generating means operative over the delay line portion of the tube.
  • One well known magnetic focusing system for this purpose comprises means for producing a substantially constant, spatially uniform, magnetic field over the electron gun region of the tube and means for producing a substantially constant so-called periodic magnetic field over the delay line region of the tube.
  • the periodic magnetic field referred to is periodic in the sense that it is spatially alternating, i.e. being first in one direction, than in the opposite direction and then in the said one direction and so on, along the length of the delay line.
  • the object of my invention is to provide a method and apparatus for compensating for the leakage field due to a magnet surrounding the gun structure of a travelling wave tube.
  • Another object of my invention is to provide a novel assembly of magnets for a magnetic focusing system in a travelling wave tube.
  • Fig. 1 is a theoretical diagram showing the distribution of a magnetic field in a travelling wave tube required for securing correct focusing
  • Fig. 2 is a cross sectional view showing the manner of assembling pairs of pole pieces in a travelling wave tube for obtaining compensation for the leakage field due to a magnet surrounding the gun structure of the travelling wave tube.
  • the full line curve A of Fig. 1 of the accompanying drawings shows in conventional graphical manner the nature of the magnetic fields required to be obtained in order to produce correct focusing.
  • the field over the electron gun region of the tube which is the region indicated by the reference G, is spatially uniform and the field over the delay line region of the tube, which is the region H, is periodic, i.e. spatially alternating.
  • the uniform field line is caused to merge smoothly into the peri- 2,965,782 Patented Dec. 20, 1960 odic field line by providing a suitable so-called matching field over the region marked M.
  • the periodic field is produced by a sequence of successively oppositely directed ring permanent magnets each having a pair of pole pieces which axially encircle the delay line portion of an inserted tube, all the pole pieces being similar and all the magnets being similar so that the said magnets with their pole pieces will, if acting alone, produce fields as shown by curve A in Fig. l for the region marked H.
  • the magnetic system employed to produce the uniform field over the region G of Fig. 1 will have substantial leakage and this affects the field produced over a portion of the delay line region near the gun region. The result is shown in Fig.
  • the object of the present invention is to avoid this defect in a simple and practically convenient manner.
  • a magnetic focusing system for a travelling wave tube includes means for producing a substantially constant spatially uniform magnetic field over the electron gun region of the tube and means for producing a substantially constant spatially alternating magnetic field over the delay line region of the tube, the last mentioned means comprising a sequence of permanent magnets, successive pairs of which, over a portion of said delay line region adjacent said gun region, have fields of diiferent strengths whereby the effect of leakage field from said first mentioned means into said portion is substantially compensated for.
  • a magnetic focusing system for a travelling wave tube includes a permanent magnet positioned to produce a substantially uniform field axially threading an inserted travelling wave tube over the electron gun region thereof, and a sequence of successively oppositely directed permanent magnets each having a pair of pole pieces positioned axially to encircle the delay line region of said inserted tube, successive pairs of said pole pieces over a portion of said delay line region adjacent said gun region being of different diameters such that the effect of leakage field from the first mentioned permanent magnet into said portion is substantially compensated for.
  • the permanent magnet producing the substantially uniform field is a ring magnet positioned axially to encircle the electron gun region of an inserted tube, and the magnets of the sequence of oppositely directed permanent magnets are also ring magnets which are in line with one another and encircle the delay line region of said inserted tube, pole piece supporting members being interposed between the successive ring members of said sequence.
  • pole piece supporting members there is only one pole piece supporting member between each successive pair of the magnets of said sequence, said member being formed to have two annular pole pieces, one on one side thereof and the other on the other, one being a pole piece appropriate to one magnet and the other being a pole piece appropriate to the next magnet.
  • the diameters of the pairs of pole pieces should be graded over the portion of the delay line region near the gun region but a practically sufiiciently close approximation to the theoretical ideal can be achieved by making alternate pairs of pole pieces (over the said portion of the delay line region) of one diameter and the other alternate pairs of pole pieces of a different diameter and it is preferred to do this for obvious reasons of manufacturing economy.
  • this shows a low noise travelling wave tube of well known type employing a helical delay line, the tube being shown inserted in position in a magnetic focusing system in accordance with this invention.
  • the tube is shown broken away at both ends and intermediately and is represented in the main merely by its envelope, though three turns of the helical delay line are shown at the broken away final electrode end of the tube.
  • the tube itself which forms no part of this invention, is of well known construction and has an envelope with an enlarged diameter portion 1 at one end continuing into a smaller diameter elongated portion 2 for the rest of its length.
  • an electron gun (not shown) adapted and arranged to project a fine beam of electrons axially down the helical delay line 3 towards the usual final electrode system (also not shown).
  • the delay line 3 of course extends over nearly the whole length of the small diameter portion of the tube envelope though, so as not to complicate the drawing, only three turns of it are actually shown.
  • the axial spatially uniform magnetic field required over the gun region of the tube is produced by a ring permanent magnet i magnetized to have opposite poles at its two ends.
  • the spatially alternating magnetic field required over the delay line region of the tube is produced by a sequence of ring permanent magnets 5, 6, 7, 8, 9, it) 11-4, n-3, n2 each of which is magnetized to have opposite poles at its two ends, the successiveisve ring magnets in this sequence being oppositely directed, i.e. there are, successively, north poles together, then south poles together, then north poles together and so on.
  • each pole piece supporting member 11 which is between two ring magnets of the sequence has two pole pieces, one of which is a pole piece appropriate to one of two successive magnets and the other of which is a pole piece appropriate to the next of said two successive magnets.
  • all the pole pieces would be alike, i.e. as shown in the broken away portion of Fig. 2 at the right hand end of that figure.
  • successive pairs of pole pieces are of different sizes over a portion of the delay line region H (Fig.
  • the pair of pole pieces 12 appropriate to the magnet are of larger diameter than the pair of pole pieces 13 appropriate to the maget 6.
  • the pole pieces 14 and 16 are of the same diameter as the pole pieces 12 while the pole pieces 17 are of the same diameter as the pole pieces 13.
  • the different pole piece diameters are chosen in accordance with known principles to compensate for the effect of leakage field from the magnet 4 in the portion of the delay line region of the tube which is affected by that leakage field. Over the remainder of the delay line region of the tube, i.e.
  • the pole pieces are in accordance with usual preseat day practice, i.e. they are all alike, as shown for the pole pieces marked P associated with the magnets n4, n-3 and 11-2.
  • the diameters of the pole pieces over the portion of the delay line region of the tube affected by leakage field from the magnet 4 should be graded, i.e. the pairs of pole pieces 12, 14 and 16 should be of progressively reducing diameters and the pairs of pole pieces 13, 17 of progressively increasing diameters, such grading being continued until, at the end of the portion of the delay line region affected by the leakage field from the magnet 4, the progressively decreased diameters and the progressively increased diameters have both reached the same value.
  • the first pole piece supporting member is identical with the next one and has a pole piece on each face.
  • the small diameter pole piece which is on the said first pole piece supporting member and which projects towards the electron gun region of the tube is unnecessary, it being provided in the illustrated arrangement only because of the convenience of using a standardised form of pole piece supporting member.
  • a magnetic focusing system for a travelling wave tube including an electron gun region and a delay line region, a permanent magnet encircling said gun region to produce a substantially uniform field axially threading an inserted travelling wave tube over the electron gun region thereof, a sequence of successively oppositely directed annular permanent magnets, of substantially uniform dimensions, pole pi ces arranged between each pair of magnets, said pole pieces being positioned axially to encircle the delay line region of said inserted tube, successive pairs of said pole pieces over a portion of said delay line region adjacent said gun region being of different diameters such that the effect of leakage field from the first mentioned permanent magnet into said portion of the delay line is subsantially compensated for.
  • a system as claimed in claim 1 wherein there is only one pole piece supporting member between each successive pair of the magnets of said sequence, said member being formed to have two annular pole pieces, one on one side thereof and the other on the other side thereof, one being a pole piece appropriate to one magnet and the other being a pole piece appropriate to the next adjacent magnet.

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  • Microwave Tubes (AREA)
  • Particle Accelerators (AREA)
US798212A 1958-03-12 1959-03-09 Magnetic focusing systems for travelling wave tubes Expired - Lifetime US2965782A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB7938/58A GB834958A (en) 1958-03-12 1958-03-12 Improvements in or relating to magnetic focusing systems for travelling wave tubes

Publications (1)

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US2965782A true US2965782A (en) 1960-12-20

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US798212A Expired - Lifetime US2965782A (en) 1958-03-12 1959-03-09 Magnetic focusing systems for travelling wave tubes

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US (1) US2965782A (en:Method)
DE (1) DE1189206B (en:Method)
FR (1) FR1222013A (en:Method)
GB (1) GB834958A (en:Method)
NL (2) NL100798C (en:Method)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3106659A (en) * 1959-03-24 1963-10-08 Kearfott Company Inc Microwave tube construction
US3259788A (en) * 1961-01-19 1966-07-05 Nippon Electric Co Magnetic focussing device for an electron tube
US3353056A (en) * 1964-04-24 1967-11-14 Gen Electric Electron beam focusing system including a magnetically permeable shield enclosing theelectron gun permanent magnet
US4057749A (en) * 1975-04-03 1977-11-08 English Electric Valve Company Ltd. Travelling wave tube having an improved magnetic focussing field
US4399389A (en) * 1980-04-01 1983-08-16 Thomson-Csf Travelling wave tube with coupled cavities and focusing by alternating permanent magnets and amplifying system comprising such a tube
US4404494A (en) * 1980-04-21 1983-09-13 Siemens Aktiengesellschaft Travelling wave tube with periodic-permanent magnet focusing system

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114256040B (zh) * 2021-12-23 2023-03-14 电子科技大学 一种新型行波管慢波结构

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2841739A (en) * 1953-04-29 1958-07-01 Bell Telephone Labor Inc Electron beam systems
US2844754A (en) * 1953-04-29 1958-07-22 Bell Telephone Labor Inc Electron beam focusing system
US2867745A (en) * 1953-10-07 1959-01-06 Bell Telephone Labor Inc Periodic magnetic focusing system
US2876373A (en) * 1956-03-01 1959-03-03 Siemens Ag Magnet system for the focusing of electron beams
US2882439A (en) * 1954-11-12 1959-04-14 Int Standard Electric Corp Travelling wave tube device
US2895066A (en) * 1954-10-04 1959-07-14 Int Standard Electric Corp Traveling wave tube
US2925519A (en) * 1954-08-26 1960-02-16 Bell Telephone Labor Inc Traveling wave tube

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2841739A (en) * 1953-04-29 1958-07-01 Bell Telephone Labor Inc Electron beam systems
US2844754A (en) * 1953-04-29 1958-07-22 Bell Telephone Labor Inc Electron beam focusing system
US2867745A (en) * 1953-10-07 1959-01-06 Bell Telephone Labor Inc Periodic magnetic focusing system
US2925519A (en) * 1954-08-26 1960-02-16 Bell Telephone Labor Inc Traveling wave tube
US2895066A (en) * 1954-10-04 1959-07-14 Int Standard Electric Corp Traveling wave tube
US2882439A (en) * 1954-11-12 1959-04-14 Int Standard Electric Corp Travelling wave tube device
US2876373A (en) * 1956-03-01 1959-03-03 Siemens Ag Magnet system for the focusing of electron beams

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3106659A (en) * 1959-03-24 1963-10-08 Kearfott Company Inc Microwave tube construction
US3259788A (en) * 1961-01-19 1966-07-05 Nippon Electric Co Magnetic focussing device for an electron tube
US3353056A (en) * 1964-04-24 1967-11-14 Gen Electric Electron beam focusing system including a magnetically permeable shield enclosing theelectron gun permanent magnet
US4057749A (en) * 1975-04-03 1977-11-08 English Electric Valve Company Ltd. Travelling wave tube having an improved magnetic focussing field
US4399389A (en) * 1980-04-01 1983-08-16 Thomson-Csf Travelling wave tube with coupled cavities and focusing by alternating permanent magnets and amplifying system comprising such a tube
US4404494A (en) * 1980-04-21 1983-09-13 Siemens Aktiengesellschaft Travelling wave tube with periodic-permanent magnet focusing system

Also Published As

Publication number Publication date
FR1222013A (fr) 1960-06-07
NL100798C (en:Method)
GB834958A (en) 1960-05-11
DE1189206B (de) 1965-03-18
NL237015A (en:Method)

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