US3903449A - Anisotropic shell loading of high power helix traveling wave tubes - Google Patents

Anisotropic shell loading of high power helix traveling wave tubes Download PDF

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Publication number
US3903449A
US3903449A US478997A US47899774A US3903449A US 3903449 A US3903449 A US 3903449A US 478997 A US478997 A US 478997A US 47899774 A US47899774 A US 47899774A US 3903449 A US3903449 A US 3903449A
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United States
Prior art keywords
helix
circuit
sectors
loading
array
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Expired - Lifetime
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US478997A
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English (en)
Inventor
Allan W Scott
Ernest A Conquest
John L Putz
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Varian Medical Systems Inc
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Varian Associates Inc
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Priority to US478997A priority Critical patent/US3903449A/en
Priority to GB2451375A priority patent/GB1475268A/en
Priority to DE19752526098 priority patent/DE2526098A1/de
Priority to CA229,163A priority patent/CA1042551A/en
Priority to FR7518539A priority patent/FR2275019A1/fr
Priority to JP50070972A priority patent/JPS5111364A/ja
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Publication of US3903449A publication Critical patent/US3903449A/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
    • H01J23/16—Circuit elements, having distributed capacitance and inductance, structurally associated with the tube and interacting with the discharge
    • H01J23/24—Slow-wave structures, e.g. delay systems
    • H01J23/26—Helical slow-wave structures; Adjustment therefor

Definitions

  • the hclix of a high power traveling wave tube i.e., in excess of ten watts cw, is supported from a thermally conductive barrel-shaped metallic envelope via the intermediary of a plurality of beryllia or boron nitride rods disposed at circumferentially spaced locations around the periphery of the helix.
  • the helix is anisotropically loaded for decreasing the positive dispersion or, in the alternative, producing a negative dispersion characteristic by means of a loading structure disposed surrounding the helix intermediate the helix and the barrel structure.
  • the loading structure comprises a plurality of arcuate quartz sectors having an array of longitudinally directed electrically conductive elements supported on the inside surface thereof adjacent the helix. ln :1 second embodiment.
  • the loading structure comprises a plurality of arcuate alumina sectors interposed between the helix and the surrounding barrel structure.
  • the present invention relates in general to anisotropic shell loading of high power helix traveling wave tubes and, more particularly, to such loading elements which are readily physically realizable for high power applications, i.e. cw power outputs in the range of 10 watts to several kilowatts.
  • the helix intercepts substantial power which products heating thereof. Because the heat cannot be conducted from the helix the helix reaches excessive operating temperatures and results in failure of the helix and therefore failure of the tube.
  • the principal object of the present invention is the provision of a high power helix traveling wave tube having increased bandwidth over which relatively high efficiency and gain are achieved.
  • anisotropic shell loading of the helix structure is obtained by use of a plurality of arcuate quartz sectors surrounding the helix in spaced relation therefrom, such quartz sectors supporting an array of longitudinally directed conductive elements on the surface thereof facing the helix for adding a negative dispersion loading effect to the otherwise positive dispersion characteristic of the traveling wave tube.
  • anisotropic shell loading of a helix is provided by means of a plurality of alumina ceramic areuate sectors disposed surrounding the helix in spaced relation therefrom and in between the helix and the barrel of the traveling wave tube, whereby a negative dispersion component is added to the otherwise positive dispersion characteristic of the traveling wave tube.
  • FIG. 1 is a longitudinal sectional schematic line diagram of a traveling wave tube of the prior art
  • FIG. 2 is a transverse sectional view of a physical realization of the structure of FIG. 1 taken along line 22 in the direction of the arrows,
  • FIG. 3 is a plot of phase velocity versus frequency showing the dispersive characteristics for the prior art and for the anisotropically loaded helix of the present invention
  • FIG. 4 is a transverse sectional view similar to that of FIG. 2 depicting a dispersion correcting structure of the prior art
  • FIG. 5 is a view similar to that of FIG. 4 depicting an alternative embodiment of the prior art
  • FIG. 6 is a view similar to that of FIG. 5 depicting an alternative embodiment of the prior art
  • FIG. 7 is a plot of interaction efficiency and gain per inch as a function of the velocity synchronism parameter (1)
  • FIG. 8 is a plot of velocity synchronism parameter (/2) as a function of frequency for two values of microperveance and depicting characteristics of the prior art and that of the present invention
  • FIG. 9 is a sectional view similar to that of FIG. 2 depicting the anisotropically shell loaded helix of the present invention.
  • FIG. 10 is a view ofa portion of the structure of FIG. 9 taken along line l0l0 in the direction of the arrows, and
  • FIG. 11 is a view similar to that of FIG. 9 depicting an alternative embodiment of the present invention.
  • the traveling wave tube I includes an elongated evacuated envelope 2 having an electron gun assembly 3 disposed at one end for forming and projecting a beam of electrons 4 over an elongated beam path to a beam collector structure 5 disposed at the terminal end of the beam path and at the other end of the tube I.
  • a helix slow wave circuit 6 is disposed along the beam path intermediate the electron gun 3 and the beam collector 5 for cumulative electromagnetic interaction with the beam to produce an amplified output signal. More particularly, RF input energy to be amplified is fed onto the helix at the upstream end thereof via an input terminal 7.
  • the microwave energy propagates along the helix in synchronism with the electrons of the beam for cumulative electromagnetic interaction to produce a growing electromagnetic wave on the circuit 6 which is extracted from the circuit at the downstream end via an output terminal 8 and thence fed to a suitable utilization device or load, not shown.
  • FIG. 2 there is shown the typical high power prior art helix support structure. More particularly, the helix 6 is supported from the inside wall of thermally and electrically conductive barrel structure 9, as of copper, which also forms the vacuum envelope of the tube via the intermediary of three electrically insulative thermally conductive refractory rods 1] as of beryllia ceramic or boron nitride.
  • the support rods 11, in one embodiment of the prior art, are captured in an interference fit between the helix 6 and the barrel 9 to provide a good thermally conductive path from the helix to the barrel 9.
  • FIG. 3 there is shown the dispersion curve 12 for the prior art tube of FIGS. 1 and 2.
  • the helix traveling wave tube has a positive dispersion characteristic over an octave of bandwidth from f to 2f,.
  • the basic principle behind traveling wave tube interaction is that the electron beam travels at approximately the same velocity as the microwave signal on the helix so that interaction is continuous along the length of the tube. If this synchronism condition is not exactly satisfied, the tube has poor gain and poor cfficiency if it is expected to operate over octave bandwidths.
  • FIG. 8 there is shown a plot of velocity synchronism parameter (b) as a function of fre quency for two values of microperveance for the same voltage of the electron beam.
  • the velocity synchronism parameter (b) varies widely over the octave of bandwidth, therefore the prior art tube with a positive dispersion characteristic, as shown by curve 12 of FIG. 3, has relatively poor efficiency and gain over the octave of bandwidth.
  • FIG. 7 there is shown the plot of interaction cfficiency in percent and gain per inch versus the synchronism parameter (/2) showing that maximum gain is obtained for a synchronism parameter ([2) value of approximately 1 and the tube has relatively high cfficiency for that value. However, the gain falls off on ei' ther side of the value of l for the synchronism parameter.
  • the anisotropic loading shell 15 as approximated by the multitude of longitudinal wires. is a boundary surrounding the helix which can conduct in the axial direc- LAJ tion but not in the circumferential direction.
  • the theoretical effect of the anisotropic shell on phase velocity is shown by curves l6 and 17 in FIG. 3 and this loading also serves to decrease the interaction impedance generally uniformly over that obtained by the unloaded cir' cuit over wide bandwidths. If the loading is sufficiently great the anisotropic shell shows anomalous or negative dispersion as shown by the curve 17. The exact amount of reduction of the dispersion of the helix depends on how close the anisotropic loading shell is brought to the helix.
  • anisotropic loading has been obtained by fluting the glass envelope structure 22 with inwardly directed projections 23 serving to support the helix 6 within the fluted glass barrel 22.
  • the gap between the helix and the glass tube reduces the dispersion of the helix.
  • negative dispersion can be achieved.
  • the glass envelope structure of FIG. 6 has the disadvantage that the thermal conductivity of the glass is relatively low so that heat is not removed from the helix via the helix support structure. As a consequence, the
  • fluted glass envelope is useful only for relatively low power applications, i.e., cw power outputs less than 10 watts.
  • the glass envelope 22 was surrounded by a thin metallic shield structure 24.
  • the glass served as an anisotropic loading structure between the helix and the shield.
  • the anisotropic loading structure 26 comprises a plurality of arcuate sectors of quartz 26 having an array of electrically conductive stripes 27 formed on the inner arcuate surface of the quartz members 26, as by photoetehing.
  • 13 line segments 27 are photoetched onto the inner surface of each of the quartz segments 26.
  • the lines 27 are 10 mils wide and the spacing between each line is l() mils. Therefore. a total of 39 conductive lines 27 are used around the circumference of the helix.
  • the quartz sectors are held to the inside wall of the bore in the envelope 9 via a plurality of metallic clips 28 which grip the sector 26 at end relieved shoulder portions 29 provided at both ends of the arcuate sectors 26.
  • the electrically conductive lines 27 are fabricated by sputtering a thin layer of molybdenum onto the inner surface of the quartz sectors 26.
  • the molybdenum coating is then copper plated.
  • the copper plated molybdenum layer is then photoetched to provide the fine line pattern.
  • the anisotropic loading shell structure 26 of FIGS. 9 and 10 as expected. reduces interaction impedance over the operating band and also provides negative dispersion.
  • the amount of negative dispersion that can be obtained for this structure is the same as would be predicted for the ideal anisotropic structure as shown in FIG. 4. In such a structure and for the structure of FIG. 9 an optimum negative dispersion is obtained when the ratio of the diameter of the conductive array to the mean diameter of the helix is approximately 1.34.
  • Curves 31 and 32 show the loading effect on the velocity synchronism parameter (I?) of the array of wires 27. From FIG. 8 it is seen that the velocity synchronism parameter (b) is much more nearly uniform over the octave bandwidth. thereby obtaining uniform gain and efficiency over an octave of bandwidth.
  • the anisotropic shell loading comprises three arcuate sectors 34 of alumina ceramic having a dielectric constant of 9.6.
  • These dielectric loading members 34 have no conductive lines printed thereon, as utilized in the embodiment of FIGS. 9 and 10. Therefore. they are more easily fabricated.
  • the resultant phase velocity for the helix circuit of FIG. 11 is almost constant with frequency over an octave of bandwidth and the interaction impedance is not reduced as much as found in the array of conductive lines on the quartz substrate as employed in the embodiment of FIGS. 9 and 10.
  • the dielectric loading sectors have an inside diameter to mean helix diameter ratio falling within the range of 1.3 to 1.4, where the ratio of the inside diameter of the barrel 9 to the mean diameter of the helix 6 falls within the range of 2.0 to 3.0.
  • the alumina ceramic loading sectors 34 an octave bandwidth was obtained between -4db points.
  • a helix type radio frequency slow wave interaction circuit disposed along the path of said stream of electrons in radio frequency energy exchanging relation therewith;
  • anisotropic loading means interposed between said circuit and said shell for making more negative the dispersion characteristic of said circuit
  • said anisotropic loading means comprising a plurality of dielectric sectors extending lengthwise of said circuit, circumferentially disposed between said dielectric support means, and abutting said metallic shell;
  • said dielectric sectors having, a dielectric constant between 9.0 and 10.0, an inner radius from the center of said circuit within the range of 1.3 to 1.4 times the mean radius of said circuit, and an outer radius within 2.0 to 3.0 times said mean radius of said circuit.
  • a helix radio frequency slow wave interaction circuit disposed along the path of said stream of electrons in radio frequency energy exchanging relation therewith for cumulative stream-field interaction with the stream to produce a growing radio frequence wave on said circuit;
  • dielectric support means circumferentially spaced apart around said helix slow wave circuit and extending along said circuit for supporting said helix from said envelope in electrically insulative and heat exchange relation therewith;
  • anisotropic loading means surrounding said helix radio frequency interaction circuit and being interposed between said envelope and said helix for adding a negative dispersion effect to the normal positive dispersion characteristic of said helix slow wave circuit, thereby obtaining a less positive or more negative dispersion characteristic
  • said loading means comprising a plurality of elongated arcuate dielectric support sectors extending along the length of said helix slow wave circuit, said support sectors including an array of elongated longitudinally directed circumferentially spaced electric conductors formed on the inner face thereof facing said helix slow wave circuit, said array of conductors surrounding said helix and being supported from the inner face of said arcuate dielectric sec tors.
US478997A 1974-06-13 1974-06-13 Anisotropic shell loading of high power helix traveling wave tubes Expired - Lifetime US3903449A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US478997A US3903449A (en) 1974-06-13 1974-06-13 Anisotropic shell loading of high power helix traveling wave tubes
GB2451375A GB1475268A (en) 1974-06-13 1975-06-06 High power helix travelling wave tubes
DE19752526098 DE2526098A1 (de) 1974-06-13 1975-06-11 Wanderfeldroehre
CA229,163A CA1042551A (en) 1974-06-13 1975-06-12 Anisotropic shell loading of high power helix traveling wave tubes
FR7518539A FR2275019A1 (fr) 1974-06-13 1975-06-13 Tube a ondes progressives de grande puissance a charge cylindrique discontinue du circuit en helice
JP50070972A JPS5111364A (ja) 1974-06-13 1975-06-13

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US478997A US3903449A (en) 1974-06-13 1974-06-13 Anisotropic shell loading of high power helix traveling wave tubes

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US3903449A true US3903449A (en) 1975-09-02

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US (1) US3903449A (ja)
JP (1) JPS5111364A (ja)
CA (1) CA1042551A (ja)
DE (1) DE2526098A1 (ja)
FR (1) FR2275019A1 (ja)
GB (1) GB1475268A (ja)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4005329A (en) * 1975-12-22 1977-01-25 Hughes Aircraft Company Slow-wave structure attenuation arrangement with reduced frequency sensitivity
US4035687A (en) * 1975-04-15 1977-07-12 Siemens Aktiengesellschaft Traveling wave tube having a helix delay line
US4107575A (en) * 1976-10-04 1978-08-15 The United States Of America As Represented By The Secretary Of The Navy Frequency-selective loss technique for oscillation prevention in traveling-wave tubes
US4153859A (en) * 1976-12-06 1979-05-08 Siemens Aktiengesellschaft Travelling wave tube with a helical delay line
US4264842A (en) * 1977-10-28 1981-04-28 Elettronica S.P.A. Helix type traveling-wave tubes with auxiliary selective shielding provided by conductive elements applied upon dielectric supports
US4292567A (en) * 1979-11-28 1981-09-29 Varian Associates, Inc. In-band resonant loss in TWT's
US4296354A (en) * 1979-11-28 1981-10-20 Varian Associates, Inc. Traveling wave tube with frequency variable sever length
FR2532109A1 (fr) * 1982-08-20 1984-02-24 Thomson Csf Tube a onde progressive comportant des moyens de suppression des oscillations parasites
US5025193A (en) * 1987-01-27 1991-06-18 Varian Associates, Inc. Beam collector with low electrical leakage
US20140292190A1 (en) * 2013-03-29 2014-10-02 Netcomsec Co., Ltd. Electron tube

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02296772A (ja) * 1989-05-09 1990-12-07 Nec Corp 進行波管支持体

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2942143A (en) * 1956-12-04 1960-06-21 Csf Travelling wave tube amplifier
US3200286A (en) * 1960-12-30 1965-08-10 Varian Associates Traveling wave amplifier tube having novel stop-band means to prevent backward wave oscillations
US3353121A (en) * 1962-09-04 1967-11-14 Csf Delay line
US3387168A (en) * 1964-12-11 1968-06-04 Varian Associates Fin-supported helical slow wave circuit providing mode separation and suppression for traveling wave tubes
US3397339A (en) * 1965-04-30 1968-08-13 Varian Associates Band edge oscillation suppression techniques for high frequency electron discharge devices incorporating slow wave circuits
US3435273A (en) * 1966-02-23 1969-03-25 Hughes Aircraft Co Slow-wave structure encasing envelope with matching thermal expansion properties
US3670197A (en) * 1971-02-25 1972-06-13 Raytheon Co Delay line structure for traveling wave devices
US3715616A (en) * 1971-10-12 1973-02-06 Sperry Rand Corp High-impedance slow-wave propagation circuit having band width extension means

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2942143A (en) * 1956-12-04 1960-06-21 Csf Travelling wave tube amplifier
US3200286A (en) * 1960-12-30 1965-08-10 Varian Associates Traveling wave amplifier tube having novel stop-band means to prevent backward wave oscillations
US3353121A (en) * 1962-09-04 1967-11-14 Csf Delay line
US3387168A (en) * 1964-12-11 1968-06-04 Varian Associates Fin-supported helical slow wave circuit providing mode separation and suppression for traveling wave tubes
US3397339A (en) * 1965-04-30 1968-08-13 Varian Associates Band edge oscillation suppression techniques for high frequency electron discharge devices incorporating slow wave circuits
US3435273A (en) * 1966-02-23 1969-03-25 Hughes Aircraft Co Slow-wave structure encasing envelope with matching thermal expansion properties
US3670197A (en) * 1971-02-25 1972-06-13 Raytheon Co Delay line structure for traveling wave devices
US3715616A (en) * 1971-10-12 1973-02-06 Sperry Rand Corp High-impedance slow-wave propagation circuit having band width extension means

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4035687A (en) * 1975-04-15 1977-07-12 Siemens Aktiengesellschaft Traveling wave tube having a helix delay line
US4005329A (en) * 1975-12-22 1977-01-25 Hughes Aircraft Company Slow-wave structure attenuation arrangement with reduced frequency sensitivity
US4107575A (en) * 1976-10-04 1978-08-15 The United States Of America As Represented By The Secretary Of The Navy Frequency-selective loss technique for oscillation prevention in traveling-wave tubes
US4153859A (en) * 1976-12-06 1979-05-08 Siemens Aktiengesellschaft Travelling wave tube with a helical delay line
US4264842A (en) * 1977-10-28 1981-04-28 Elettronica S.P.A. Helix type traveling-wave tubes with auxiliary selective shielding provided by conductive elements applied upon dielectric supports
US4296354A (en) * 1979-11-28 1981-10-20 Varian Associates, Inc. Traveling wave tube with frequency variable sever length
US4292567A (en) * 1979-11-28 1981-09-29 Varian Associates, Inc. In-band resonant loss in TWT's
FR2532109A1 (fr) * 1982-08-20 1984-02-24 Thomson Csf Tube a onde progressive comportant des moyens de suppression des oscillations parasites
EP0102288A1 (fr) * 1982-08-20 1984-03-07 Thomson-Csf Tube à onde progressive comportant des moyens de suppression des oscillations parasites
US4559474A (en) * 1982-08-20 1985-12-17 Thomson-Csf Travelling wave tube comprising means for suppressing parasite oscillations
US5025193A (en) * 1987-01-27 1991-06-18 Varian Associates, Inc. Beam collector with low electrical leakage
US20140292190A1 (en) * 2013-03-29 2014-10-02 Netcomsec Co., Ltd. Electron tube
US9196448B2 (en) * 2013-03-29 2015-11-24 Nec Network And Sensor Systems, Ltd. Electron tube

Also Published As

Publication number Publication date
FR2275019A1 (fr) 1976-01-09
DE2526098A1 (de) 1976-01-02
CA1042551A (en) 1978-11-14
GB1475268A (en) 1977-06-01
JPS5111364A (ja) 1976-01-29
FR2275019B1 (ja) 1979-07-13

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