US2947905A - Low noise velocity modulation apparatus - Google Patents

Low noise velocity modulation apparatus Download PDF

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Publication number
US2947905A
US2947905A US471673A US47167354A US2947905A US 2947905 A US2947905 A US 2947905A US 471673 A US471673 A US 471673A US 47167354 A US47167354 A US 47167354A US 2947905 A US2947905 A US 2947905A
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United States
Prior art keywords
noise
cathode
velocity
electron
electrons
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Expired - Lifetime
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US471673A
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English (en)
Inventor
John R Pierce
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AT&T Corp
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Bell Telephone Laboratories Inc
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Publication date
Priority to NL198433D priority Critical patent/NL198433A/xx
Priority to DENDAT1071851D priority patent/DE1071851B/de
Priority to BE542850D priority patent/BE542850A/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US471673A priority patent/US2947905A/en
Priority to FR1134058D priority patent/FR1134058A/fr
Priority to GB33079/55A priority patent/GB806890A/en
Application granted granted Critical
Publication of US2947905A publication Critical patent/US2947905A/en
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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
    • H01J23/06—Electron or ion guns
    • H01J23/065—Electron or ion guns producing a solid cylindrical beam
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/005—Gas-filled transit-time tubes

Definitions

  • An object of the present invention is yto improve the signal-to-noise ratio (or, noise vfigure) Vinvelocity modulation-type amplifiers, for example, of the'kl'ystron and traveling wave tube type.
  • -f 'l A more specific object is in such amplifiers -to minimize the eifect on the signal circuits associatedwith the electron beam of shot noise in the current' emitted from a thermionic cathode.
  • y It is characteristic in velocity modulation-typeamplifiers that an electron beam whichhas been-space-chargelimited is projected past an input arrangement ⁇ which impresses signal modulations on the-beam and such modulations are thereafter used in setting up an ampli fied electromagnetic wave 'in an output arrangement.
  • IInv a klystron the input and output arrangements each com' prise a cavity resonant at theoperating frequency.
  • 'In a traveling wave tube the input and output arrangements comprise opposite ends of a slow Wave interaction circuit.
  • the present invention relates still-more particularly to an arrangement which Vreduces specifically the effect of noiseconvection current near the cathode.
  • Accordi'nglyjthe invention has primary application in combi-,-
  • a space-charge-limited beam is one which obeys Ch'lds law, i.e., only a fraction of 'the electrons emitted is drawn off to yform the beam, the remainder returningv to the cathode through the agency of a potential minimum in a region adjacent to the front of the cathode, so that for further increases in cathode emission in the absence of changes in the Vaccelerating potential only a small change in the beam current results.
  • a space-charge-lmited region is one where the space charge forces in the direction of flow are so strong vthat they limit the ow and sothe net lcurrent in the beam is appreciably affected by changes in the accelerating field.
  • a vfea'tureof .thenven-f tion is an electron permeable control member or ele'cl- V trode positioned close to the cathode and biased with respect thereto for acting to confine the region' affecting the return of electrons to the cathode to'theY short inter'- space formed between it and the cathode.
  • the cathodeand the control electrode are made to form opposite surfaces vof a cavity substantially resonant atthe operating frequency to provide a high radio frequency'impedance acrossthe" space-charge-limited region.
  • this expedient there is, ⁇ further reduced in the beam passing beyond the control electrode noiseV convection components characteristic of. the frequencies in the operating band.
  • y j 1 It is important that this smoothing cavity be asfclose' to the electron source as possible ⁇ since ,there thexrroise velocity fluctuations and noise Vconvection current are'stillv substantially uncorrelated audit ispossibler to reduce ⁇ one without affecting the other.
  • the path of ow from the cathode surface correlation' between the two types of noise develops and it becomes difficult to iaiect one independently of the other.
  • a control grid is positioned in front of the cathode and maintained at a suitable D.C. potential with respect thereto for deiining the space-charge-lirnited portion of the path of ow of the electrons, and the cathode and the control grid are designed to form opposite surfaces of a cavity resonant at the operating frequency.
  • This arrangement serves to keep small the noise convection current which ordinarily sets up noise waves of frequencies in the operating band.
  • an electrode system focuses the electrons penetrating there past into a beam and thereafter accelerates the beam to a velocity suitable for permitting interaction with the slow wave on the interaction circuit.
  • this electrode system also provides a velocity jump in the electron beam at a point of noise velocity maximum to attenuate the noise velocity fluctuations on the beam.
  • the wave interaction circuit is located beyond the electrode system at a point which preferably is chosen experimentally for lowest noise.
  • Fig. l shows in longitudinal cross section a traveling wave amplifier constructed in accordance with the invention for improved signal-to-noise ratio
  • Fig. 2 shows in longitudinal cross section an electron gun which can be incorporated in the tube of Fig. l in place of the electron gun shown therein.
  • the various tube elements are housed in an evacuated envelope 11, for example, of glass or quartz.
  • an electron gun 12 serves as the source of electrons which are formed into a beam for projection axially through the envelope to a target electrode 13 housed at the opposite end.
  • a slow wave circuit 14 shown, for example, as a helical conductor, propagates an electromagnetic wave in field coupling relation with the beam fory interaction therewith over a plurality of operating wavelengths.
  • An input connection 15 to the Iupstream i.e.
  • the tube is of familiar form.
  • the tube is modied by the inclusion of a novel foi-1n of electron gun.
  • the electron gun 12 comprises a conductive heater compartment 20 which houses the heater filament 21 and one surface 22 of which is coated to be electron emissive when heated to serve as the thermionic cathode of the gun.
  • an electron permeable control electrode member 23 Spaced close to the cathode is an electron permeable control electrode member 23, shown, for example, as a very fine grid, which is maintained at a potential slightly negative with respect to the cathode so that electron current interception thereby is minimized.
  • the member 23 is positioned sufliciently close to the cathode so that its presence rather than that of the potential minimum effectively controls the current at the frequency of operation. Either it should 'be so close to the cathode that there is nopotential minimum between it and the cathode, or it should be very close to the potential.
  • the space charge forces in the direction of flow ⁇ do not serve to limit the ow.
  • changes in potential in this region have little eiect on the amount of current flow passing the grid 23.
  • beam forming electrode 24 advantageously serves to form the electrons which penetrate beyond the control elect-rode 23v into a solid electron beam, one preferably circular in cross section.
  • the beam forming electrode 24, too, is ⁇ advantageously maintained at a slightly negative potential with respect to the cathode.
  • the roles of the control electrode 23 and the beam forming electrode 24 in a single electrode which will serve both to confine the space-charge-limited region of ow to only a short initial portion of the path of flow as discussed above and to form the electrons into a beam for ow beyond this initial portion.
  • the rlirst accelerating anode 25 which is operated at an intermediate positive potential with respect to the cathode 22 and serves to accelerate the electrons in the beam.
  • the accelerating electrode 25 comprises a circular flange like portion 25A and an elongated tubular portion 25B surrounding the path of flow and forming a rst drift region.
  • a second accelerating anode 26 which is an elongated tube surrounding the path of ilow and forms a second drift region along the path of ow.
  • the second accelerating anode 26 is maintained at a high positive potential for accelerating the electron beam to a velocity substantially equal to the axial phase velocity of the wave propagating along the slow wave circuit 14.
  • the gap 27 between the first and second ⁇ accelerating anodes is made nonresonant and located experimentally at a point along the path of flow which corresponds to a noise velocity maximum.
  • the cathode 22 and the control electrode 23 form opposite surfaces of a cylindrical cavity 29 which is resonant at the mfidfrequency of the operating band to be amplified.
  • the cavity 29 is constricted in its center tov define there a short gap between its two opposite surfaces including the cathode and control grid.
  • This gap is advantageously short since it represents the space-charge-limited portion of the path of flow which should be short for low noise convection current.
  • a D.C. potential may be set up therebetween and yet to maintain continuity for.
  • the cavity includes a tubular portion ⁇ 30 which surrounds the heaterv compartment 20 spaced therefrom by insulating spacers.
  • the geometry of the gap formed between the heater compantment and the tubular portion 3:0y is adjusted so that the gap acts as a quarter wavelength choke at the operating frequency.
  • This arrangement minimizes leakage from the cavity and yet makes feasible D.C. isolation of the cathode and control pontions of the cavity.
  • the slow wave circuit 14 is advantageously operated at the same D.C. potential as the second accelerating anode 26 in order to avoid further velocity discontinuities in the beam. Accordingly, one end of the helical conductor 14 is connected to the second accelerating anode 26. For minimum noise, there is an optimum location along the beam path for the-start of the slow wave circuit, but such location is best found experimentally for a given set of operating parameters.
  • the buncher cavity In a klystron, the buncher cavity would be similarly located experimentally at a point of minimum noise and operated at the same D.C. potential as the last accelerating anode.
  • Such focusing forces can be provided by a longitudinal magnetic field.
  • the auxiliary equipment for providing the longitudinal magnetic field As is known to workers inthe ant, if magnetic focusing of the kind described as Brillouin focusing is employed, it is important to shield the cathode from the magnetic field.
  • the flange like portion A of the rst accelerating anode 25 can advantageously be made of magnetic material and used as a magnetic shield.
  • a grid be employed as the control element.
  • Fig. 2 there is shown a modified gun 40 which can be used in the tube of Fig. 2 in place of electron gun 12.
  • the heater compartment 41 which houses the heater filament 42 has a constricted end portion 43 which is coated to be electron emissive for serving as the cathode.
  • the electron permeable control electrode is formed by a conductive surface 44 which is positioned close to the cathode and apertured for passage of the electrons therepast. The various factors involved in its positioning are the same as were discussed above.
  • the conductive surface 44 together with the heater compartment 41 form opposite surfaces of a cavity 45 resonant at the middle of the operating frequency band. In order to permit the establishing of a DHC.
  • the cavity includes a dielectric ring 46 which has no effect on radio frequency currents bu-t does isolate for D.C. the cathode and control element portions of the resonant cavity 45.
  • Suitable lead-in connections from a D.C. voltage source maintain the control element at a small negative D.C. potential with respect to the cathode.
  • a beam forming electrode 48 forms the electrons passing through the aperture in the control surface 44 intoa solid cylindrical beam. Accelerating anodes 49 and 50, corresponding to the accelerating anodes 25 and 26 of electron gun 12 shown in Fig. l, provide a velocity jump at the nonresonant gap 51 for reducing noise velocity fluctuations in the beam.
  • an electron beam formed in the manner described to have snall noise convection current vand'noise velocity lfluctuations may be modulated by a, buncher cavity supplied with an input signal and used to induce an output signal in a catcher cavity in the manner characteristic of klystron operation.
  • various modifications may be made in the electron gun proper consistent with the principles of the invention.
  • the cathode may be of the hollow cathode type of the kind described in United States Patents 2,810,088, 2,810,089 and 2,810,090,'all issued October 10, 1957, of D. MacNair, and the hollow cathode may itself be constructed to act as a cavity resonant at the operating frequency. Additionally, for some applications a sufiicient improvement in noise figure may be had merely by reducing the noise convection current in the manner described to obviate the necessity of also reducing the noise velocity rfluctuations in the beam so that a velocity jump may be omitted. Moreover, noise due to velocity fluctuations may be reduced by any of the techniques described United States Patent 2,828,439, issued March 25, 1958, of R. C. Fletcher.
  • an electron emissive cathode surface a control element located between the cathode surface and means for modulation o-f electron flow therefrom and spaced closed to said surface for space-charge-limiting the ow therefrom, means for providing a high R-F impedance across said spacecharge-limiting region, said means including the cathode and control element forming opposite surfaces of a cavity which is resonant at the midfrequency of the operating band of the apparatus, and means positioned along the path of flow beyond said control element for imparting a velocity jump to the electrons at a point of noise velocity maximum.
  • an electron emissive cathode for serving as a source of an electron beam
  • a control element located between the cathode and means for modulation of said beam and spaced close to said cathode for space-charge-limiting the flow therefrom
  • means for providing a high R-F impedance across the space-charge-limiting region said means including the cathode and control element forming opposite surfaces of a cavity which is resonant at the midfrequency of the amplifying band of the tube, first and second accelerating anodes positioned along the path of ow beyond said control element and maintained at successively higher D.C.
  • means for reducing the noise convection current in the beam characteristic of frequencies in the operating band of said apparatus including a cathode emissive surface which is the source of the electron beam and a control element for space-chargelimiting the flow of the electrons from said cathode emissive surface, said control element being located between the cathode and means for modulating said beam and spaced from said emissive surface a distance the transit time of which for the electrons in the beam is short relative to the period of frequencies in the operating band of the apparatus, and means for providing a high R-F impedance across said space-charge-limitng region, said 7 means including the cathode and control element forming opposite surfaces 0f a cavity resonator which is substantially closed and free of coupling providing excitation from an external source and which is resonant at the mid-frequency of the operating band of the apparatus.

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  • Microwave Tubes (AREA)
  • Particle Accelerators (AREA)
US471673A 1954-11-29 1954-11-29 Low noise velocity modulation apparatus Expired - Lifetime US2947905A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL198433D NL198433A (no) 1954-11-29
DENDAT1071851D DE1071851B (no) 1954-11-29
BE542850D BE542850A (no) 1954-11-29
US471673A US2947905A (en) 1954-11-29 1954-11-29 Low noise velocity modulation apparatus
FR1134058D FR1134058A (fr) 1954-11-29 1955-07-06 Appareil à modulation de vitesse à faible bruit
GB33079/55A GB806890A (en) 1954-11-29 1955-11-18 Improvements in or relating to velocity modulation apparatus and electron guns therefor

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US471673A US2947905A (en) 1954-11-29 1954-11-29 Low noise velocity modulation apparatus

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US2947905A true US2947905A (en) 1960-08-02

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US471673A Expired - Lifetime US2947905A (en) 1954-11-29 1954-11-29 Low noise velocity modulation apparatus

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US (1) US2947905A (no)
BE (1) BE542850A (no)
DE (1) DE1071851B (no)
FR (1) FR1134058A (no)
GB (1) GB806890A (no)
NL (1) NL198433A (no)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3215890A (en) * 1961-05-22 1965-11-02 Zenith Radio Corp Electron gun structure for producing an electron beam free of radial velocity components wherein the length of the first non-magnetic cylinder is approximately equal to an integral number of wave lengths of the scallop frequency
US3377492A (en) * 1965-08-03 1968-04-09 Hughes Aircraft Co Flood gun for storage tubes having a dome-shaped cathode and dome-shaped grid electrodes
US3448313A (en) * 1966-10-10 1969-06-03 Varian Associates Efficient radiation cooled beam collector for linear beam devices
US4321505A (en) * 1978-07-24 1982-03-23 Varian Associates, Inc. Zero-bias gridded gun
US5233269A (en) * 1990-04-13 1993-08-03 Varian Associates, Inc. Vacuum tube with an electron beam that is current and velocity-modulated
FR2840104A1 (fr) * 2002-05-27 2003-11-28 Nec Microwave Tube Ltd Canon a electrons

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL105096C (no) * 1954-08-05

Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2425748A (en) * 1941-03-11 1947-08-19 Bell Telephone Labor Inc Electron discharge device
US2455269A (en) * 1942-11-17 1948-11-30 Bell Telephone Labor Inc Velocity variation apparatus
US2484643A (en) * 1945-03-06 1949-10-11 Bell Telephone Labor Inc High-frequency electronic device
US2494721A (en) * 1947-06-18 1950-01-17 Bell Telephone Labor Inc Electron velocity variation device with noise reducing resonator
US2595698A (en) * 1949-05-10 1952-05-06 Rca Corp Electron discharge device and associated circuit
US2641733A (en) * 1951-01-08 1953-06-09 Collins Radio Co High-frequency tube
US2681951A (en) * 1948-09-01 1954-06-22 Csf Low background noise amplifying system for ultra-short waves
US2720610A (en) * 1950-07-27 1955-10-11 Kazan Benjamin Noise reducing travelling-wave tube
US2767259A (en) * 1952-10-01 1956-10-16 Rca Corp Noise compensation in electron beam devices
US2800603A (en) * 1952-04-08 1957-07-23 Itt Traveling wave electron discharge devices
US2800602A (en) * 1951-06-05 1957-07-23 Univ Leland Stanford Junior Low noise electron discharge tubes
US2810853A (en) * 1950-12-01 1957-10-22 Int Standard Electric Corp Electron discharge apparatus
US2813222A (en) * 1951-05-11 1957-11-12 Philips Corp Travelling wave tube
US2832001A (en) * 1954-08-27 1958-04-22 Zenith Radio Corp Electron discharge systems

Patent Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2425748A (en) * 1941-03-11 1947-08-19 Bell Telephone Labor Inc Electron discharge device
US2455269A (en) * 1942-11-17 1948-11-30 Bell Telephone Labor Inc Velocity variation apparatus
US2484643A (en) * 1945-03-06 1949-10-11 Bell Telephone Labor Inc High-frequency electronic device
US2494721A (en) * 1947-06-18 1950-01-17 Bell Telephone Labor Inc Electron velocity variation device with noise reducing resonator
US2681951A (en) * 1948-09-01 1954-06-22 Csf Low background noise amplifying system for ultra-short waves
US2595698A (en) * 1949-05-10 1952-05-06 Rca Corp Electron discharge device and associated circuit
US2720610A (en) * 1950-07-27 1955-10-11 Kazan Benjamin Noise reducing travelling-wave tube
US2810853A (en) * 1950-12-01 1957-10-22 Int Standard Electric Corp Electron discharge apparatus
US2641733A (en) * 1951-01-08 1953-06-09 Collins Radio Co High-frequency tube
US2813222A (en) * 1951-05-11 1957-11-12 Philips Corp Travelling wave tube
US2800602A (en) * 1951-06-05 1957-07-23 Univ Leland Stanford Junior Low noise electron discharge tubes
US2800603A (en) * 1952-04-08 1957-07-23 Itt Traveling wave electron discharge devices
US2767259A (en) * 1952-10-01 1956-10-16 Rca Corp Noise compensation in electron beam devices
US2832001A (en) * 1954-08-27 1958-04-22 Zenith Radio Corp Electron discharge systems

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3215890A (en) * 1961-05-22 1965-11-02 Zenith Radio Corp Electron gun structure for producing an electron beam free of radial velocity components wherein the length of the first non-magnetic cylinder is approximately equal to an integral number of wave lengths of the scallop frequency
US3377492A (en) * 1965-08-03 1968-04-09 Hughes Aircraft Co Flood gun for storage tubes having a dome-shaped cathode and dome-shaped grid electrodes
US3448313A (en) * 1966-10-10 1969-06-03 Varian Associates Efficient radiation cooled beam collector for linear beam devices
US4321505A (en) * 1978-07-24 1982-03-23 Varian Associates, Inc. Zero-bias gridded gun
US5233269A (en) * 1990-04-13 1993-08-03 Varian Associates, Inc. Vacuum tube with an electron beam that is current and velocity-modulated
FR2840104A1 (fr) * 2002-05-27 2003-11-28 Nec Microwave Tube Ltd Canon a electrons

Also Published As

Publication number Publication date
BE542850A (no)
DE1071851B (no)
NL198433A (no)
GB806890A (en) 1959-01-07
FR1134058A (fr) 1957-04-05

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