US2986672A - Periodic electrostatically focused beam tubes - Google Patents

Periodic electrostatically focused beam tubes Download PDF

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Publication number
US2986672A
US2986672A US780783A US78078358A US2986672A US 2986672 A US2986672 A US 2986672A US 780783 A US780783 A US 780783A US 78078358 A US78078358 A US 78078358A US 2986672 A US2986672 A US 2986672A
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Prior art keywords
electrodes
potential
focusing
diameter
electrode
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Expired - Lifetime
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US780783A
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English (en)
Inventor
Frank E Vaccaro
Wieslaw W Siekanowicz
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RCA Corp
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RCA Corp
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Priority to NL246440D priority Critical patent/NL246440A/xx
Priority to NL104255D priority patent/NL104255C/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US780783A priority patent/US2986672A/en
Priority to GB39543/59A priority patent/GB925551A/en
Priority to FR810764A priority patent/FR1240982A/fr
Priority to DER26884A priority patent/DE1264622B/de
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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
    • H01J23/083—Electrostatic focusing arrangements

Definitions

  • This invention relates to electron beam devices, and particularly, to such devices having periodic electrostatic means for focusing the beam.
  • the principal object of-the present inven tion is to provide a periodic electrostatic beam-focusing means that will maintain the diameter of the beam substantially constant along an extended beam path.
  • Another object is to provide an improved periodic beam focusing electrode structure.
  • the diameter of the beam in an electron beam device is maintained substantially constant by establishing a periodic electrostatic focusing viield along the beam path having substantially the same potential variation between given minimum and maximum potentials in each half-period along the path that would exist along an electron stream having innite transverse dimensions and the same current density passing at right angles through a pair of grids maintained at the given minimum and maximum potentials.
  • This desiredpotential variation has been closely approximated by mounting a multiplicity of very thin apertured plates in alignment along the beam path in each period and applying a separatepotential to each plate.
  • a Amore practical arrangement comprises a set of apertured plate electrodes at a high potential alternating along the beam path with a set of elongated hollow electrodes at a low potential suitably shaped internally to approximate the desired potential variation.
  • the best approximation of the ideal potential variation is obtained when each of the focusing electrodes is provided with a grid extending across the beam path.
  • the electron beam can be introduced at one end of the periodic focusing structure at the desired diameter by any conventional means, such as aV parallel-flow gun or a convergent-How gun, as shown on pages 178 and 189 of the Pierce textbook referred to above. s
  • Fig. 1 is a schematic representation to be referred to.
  • FIG. 2 is a graph showing the potential variation bei-'- tween two grids in a theoretical electron device having/an electron flow of iniinite transverse dimension
  • Fig. 3 is a graph showing the normalized current unde the conditions of Fig. 2 as a function of the voltage of-4 the lower potential grid, for a given high potentialgrid.
  • Fig. 4 is a graph showing the normalized perveance as a function of the voltage of the lower potential grid
  • Fig. 9 is a graph showing the potential variations obtained in an electrolytic tank for the focusing structures shown in Figs. 6, 7 and 8, respectively, in comparison with the ideal variation shown in Fig. 2;
  • v l Fig. 10 is an axial sectional view of a tw0CeVi2Yk1y stron tube having a convergent-now gun and incorporating the present invention.
  • Fig. 11 is an axial sectional view of the gun portion o f a klystron similar to that shown in Fig. 10 but having a parallel-How gun. ...f
  • Fig. l schematically shows a series of grids G having infinite dimensions normal to an x coordinate. Assume that alternate grids are connected together, and that one set of grids is maintained at a Agiven low positive D.C. potential V1, and the other set at a given high positive D.C. potential VH. In the absence of space charge (zero current) the potential distribution between the two grids is linear, as shown by the dashed straight line A in Fig. 1. If an electron stream having innite transverse dimensions, uniform current density and elec.- tron trajectories parallel to the x axis is injected at the initial plane OL, the presence of space charge will depress the potential between the grids. In Fig. 1, the curve B represents the actual potential variation in an electron ow of infinite width between adjacent grids under the' condition: v
  • Patented May 30, 1.961 Patented May 30, 1.961.
  • the potential distribution (curve B) in each of regions HL is a mirror image of the parabolic curve in the regions LH.
  • the entire potential distribution curve B is made up of a series of double-parabolic sections joined together with a cusp, or abrupt change in sign of the slope of the curve, at each high potential plane. Because the transverse dimensions are infinite, the variation of the D.C. potential in the transverse direction (r) is zero, i.e.:
  • Equation 2 can be transformed mathematically to the following equation:
  • Equation 5 the term x0 in .Equation 2 is the distance over which a ⁇ potential VL will vproduce a current density I in a space-charge-saturated diode having an anodepotential VL.
  • the present invention is based on the concept that an electron beam of finite dimensions could be perfectly confined or focused to maintain constant dimensions along an extended path if one could establish vthe same parabolic potential variation along the beam path that exists in the hypothetical infinite-grid model shown in Fig. l. It is, of course, .impossible to exactly duplicate this ideal .condition along a beam of finite dimensions. However, ⁇ it will .be shown how to closely approximate the ideal condition by utilizing periodic electrostatic focusing structure that will establish a satisfactory potential variation that does not differ substantially from the ideal potential variation of Fig. l as shown by curve B.
  • the transit time is given :by:
  • the effective-voltage, Ve is:
  • Fig. 4 shows a plot of normalized perveance, P/Pm, as' a function of VL/VH.
  • Fig. 5 schematically shows an experimental electron beam -tube that was constructed to verify the theory on which the invention is based.
  • the tube comprises an elongated vacuum envelope 1 containing an electron gun 3 at one end and a collector 5 at the other end, defining an extended beam path therebetween.
  • the gun 3 comprises a large-area concave cathode 7, heater 9, focusing electrode 11 and two accelerating electrodes 13 and 15 arranged to produce an electron beam converging from a large cross sectional area at the cathode to a given smaller area in the plane of the second accelerating electrode 15 where the convergent action of the gun is overcome by space charge forces to produce substantially parallel ow.
  • a periodic electrostatic focusing structure made up of a multiplicity of identical thin apertured plate focusing electrodes 17 which are mounted close together in alignment along the beam path between electrode 15 and collector 5.
  • electrode 15 which is also a thin apertured plate, serves also as the first electrode of the iirst period of the focusing structure.
  • Electrode 15 is connected to the 8th, 16th, 24th, 32nd, 40th, and 48th electrodes 17 and to an external D.C. voltage source 18 to establish a high potential, VH, at each end of each period.
  • each intermediate electrode 17 in each period is connected to corresponding electrodes 17 in the other periods and connected to external leads to permit the establishment of any desired potential distribution, VH--VL-VH, within each period, as shown by the potential curve in Fig. 5.
  • the focusing electrodes 15 and 17 were connected to voltage sources providing a parabolic potential distribution V(x) in each period as determined from Equation 4 for a given minimum potential VL and a given beam current density I.
  • V(x) a parabolic potential distribution in each period as determined from Equation 4 for a given minimum potential VL and a given beam current density I.
  • the design of shaped focusing electrodes approximating the ideal boundary conditions of Equation 4 at the edge of the beam for a smaller member of electrodes per period can be determined by use of an electrolytic tank technique similar to that used for designing Pierce-type electron guns (see pages 179 and 180 of the Pierce textbook referred to above). There is a large number of electrode shapes which will approximate the ideal boundary conditions, and several specific electrode shapes will bev disclosed as examples only.
  • Equations 3 and 4 are satisfied throughout the region occupied by the beam. Measurements made in an electrolytic tank have shown that these conditions can be very closely approximated by electrodes of the shapes shown in Fig. 6 for each period of an alternative periodic focusing structure to be substituted for the focusing electrodes 15 and 17 of Fig. 5.
  • electrodes 15 and 17 are essentially the same as the corresponding high potential electrodes at the beginning and end of each period in Fig. 5.
  • the (seven) intermediate electrodes 17 in each period in Fig. 5 are replaced by a single annular low potential electrode 19 having a double-conical inner surface 21 with a minimum diameter at lthe central plane equal to the diameter of the aperture in the plate electrodes 15 and 17 and not substantially larger than the beam diameter d.
  • a thin mesh grid 23 is mounted across the beam path in the :central plane of each electrode, as shown.
  • the length 6 of each period is about 1.7 times the beam diameter d.
  • Annular electrode 19 has an axial length of about .8d and a maximum inner diameter at each end of about 1.6d.
  • the minimum thickness of the plate electrodes 15 and 17 is about .03d.
  • the potential distribution obtained in the electrolytic tank using the electrode shapes shown in Fig. 6 is plotted with dots 16 in Fig. 9 for comparison with the ideal curve 20 of Fig. 2. As shown, the dots almost coincide with the ideal curve.
  • the inner diameter of the beam apertures in the focusing electrodes 15', 17 and 19' is 1.34 times the beam diameter d and the period is 2.3d.
  • the low potential electrode 19 has an axial length of about 1.25d and a maximum inner diameter at each end of about 1.74d.
  • the thickness of the high potential electrode is about .14d.
  • the potential distribution obtained with the electrodes of Fig. 7 is shown as the short-dash curve 18 in Fig. 9.
  • the aperture diameter is 1.7d and the period is 2.9d.
  • the low potential electrode 19" has a length of 1.73d and a maximum inner diameter of 1.9ld. 'The thickness of electrodes 15 and 17" is about .15d.
  • the potential distribution obtained with the electrodes of Fig'. 8 is shown as the long-dash curve 22 in Fig. 9.
  • the ideal potential distribution at the beam boundary is shown as the solid curve in Fig. 9.
  • the period should be at least 1.5d and the beam diameter should be at least one half of the electrode aperture diameter.
  • the gridless elec'- trodes can closely approximate the ideal potential .distribution at the beam boundary.
  • the difference between the maximum and minimum inner diameters of the elongated low potential electrodes 19 is less than the minimum inner diameter.
  • Fig. lO shows the present invention incorporated, Lfor example, in a two-cavity klystron tube.
  • the tube comprises, from left to right, a convergent-flow electron ⁇ gun 25, an input or velocity modulating cavity ,resonatorAZIL an elongated drift tube structure 29, an output cavity resonator 31, and a collector 33.
  • the electron gun 25 comprises a large-area concave cathode 35, heater 37, focusing electrode 39 and accelerating electrodes 41 and 43-arranged to inject a high density parallel-flow beam into the input resonator 27.
  • the outer peripheries of the gun electrodes are interposed between and sealed to ceramic rings 45 to provide insulation therebetween and form part of the vacuum envelope of the tube.
  • the gun 2S is mounted on the input resonator 27 by another ceramic ring 47.
  • the collector 33 is mounted on the output resonator 31 by a ceramic ring 49.
  • the drift tube structure 29 and the beam apertures in the input and output resonators 27 and 31 are formed as a series of periodic beam focusing electrodes of the kind shown in Figs. 6 to 8.
  • the nal accelerating electrode 43 of the gun also forms the rst high potential focusing electrode.
  • the focusing electrodes comprise a set of annular low potential electrodes 51 having double-conical inner surfaces like electrode 19 in Figs. 6 to 8 alternating with apertured plate high potential electrodes S3.
  • the first two of electrodes 51 are mounted through the walls of the input resonator 27, and the last two are similarly mounted in the output resonator 31.
  • the first and last of electrodes 53 are mounted in the resonators 27 and 31, respectively.
  • Each of the plate electrodes 53 in the drift tube region is mechanically connected to each adjacent annular electrode 51 in insulated and sealed relation by means of an apertured ceramic disc 55 sealed at its inner edge to the outer surface of electrode 51 and at its outer periphery to a metal ring 57 sealed to the electrode 53 and having an inner ange 58.
  • Each of the annular electrodes 51 in the drift region is provided at each end with an apertured disc 59 extending outwardly to about the inner edge of the ange 58 of the nearest ring 57.
  • the radial dimension of each disc 59 and the flange 58 of each ring 57 is made approximately a quarter wavelength at the operating frequency of the tube, so that the quarter wave open line formed by the disc 59 and electrode 53 combined with the quarter wave closed line formed by the ring 57 and electrode S3 will form a broadband radiofrequency short circuit between adjacent electrodes 51 and 53.
  • Each of the plate electrodes 53 in the input and output resonators is similarly mounted by radiofrequency choke made up of a ceramic ring 61 and flanged discs 63 and 65, to produce a wideband radiofrequency short circuit in the plane of disc 65.
  • Each of the input and output resonators 27 and 31 is provided with a radiofrequency coupling means, such as a coupling loop 66.
  • Fig. l1 is a fragmentary view of a modification of Fig. 10, in which a parallel-how gun 67 is used.
  • the gun 67 comprises a plane cathode 69, a heater 71, and a focusing electrode 73, with ceramic rings 75.
  • the rst annular low ⁇ potential electrode 51 of Fig. 10 is replaced by an annular electrode A'77 having a single diverging conical inner surface, which electrode serves as the sole accelerating electrode of the gun and also as the low potential electrode of a starting half period of the periodic focusing system, as shown by the potential curve in Fig. 1l.
  • This potential curve also shows the diode distribution between the cathode and electrode 77.
  • Fig. 1l also shows a modified choke mounting for the high potential plate electrode in the input resonator 78, which comprises a pair of apertured ceramic discs 79, a first pair of flanged rings 81 and a second pair of flanged rings 83.
  • the resonator 78 is provided with suitable radiofrequency coupling means (not shown).
  • the remainder of the tube of Fig. 11 is essentially the Same as that of Fig. 10.
  • An electron beam tube comprising an electron gun f or producing an electron beam of given ,transverse k,dimensions ⁇ t a ,given transverse Platte elena .an extended beam path, and means including a series of spaced focusing electrodes aligned along said path beyond Said plane for establishing along said path a periodic electrostatic focusing field having a plurality of periods and having substantially the same parabolic potential variation between given transverse planes of minimum and maximum potential in each half-period at the boundary of said beam as an electron ow along said path having infinite transverse dimensions and the same current density pass ing at right angles through a pair of grids maintained at said given minimum and maximum potential planes, for maintaining said beam dimensions substantially constant beyond said rst named plane.
  • a n electron beam tube comprising an electron gun for producing an electron beam of given dimensions at a given transverse plane along an extended beam path, and means including a series of spaced focusing electrodes aligned along said path beyond said plane for establishing along said path a periodic electrostatic focusing iield having a plurality of periods with a parabolic potential variation V(x) in each period, at least at the boundary of said beam, substantially determined by the equation:
  • VL the minimum value of the potential in each period
  • V(x) the potential in a plane at a distance x from the plane of VL, where x a half period
  • J the current density of the beam in amperes per square meter
  • a beam tube as in claim l wherein said series of focusing electrodes comprises a first set of high potential apertured plate electrodes alternating with a second set of low potential elongated hollow electrodes, the inner surface of each of said hollow electrodes increasing from a minimum dimension near the center to a larger dimension at each end.
  • each of said hollow electrodes has an axial length about 0.8 times the beam diameter and a maximum inner diameter at each end about 1.6 times the beam diameter, and the thickness of each of said plate electrodes is not greater ⁇ than about 0.03 times the beam diameter.
  • each of said hollow electrodes has an axial length about 1.25 times the ⁇ beam ⁇ diameter and a 4maximum inner diameter at 9 each end about 1.74 times the beam diameter, and the thickness of each of said plate electrodes is about 0.14 times the beam diameter.
  • An electron beam tube comprising an electron gun for producing an electron beam of given diameter at a given transverse plane along an extended beam path, and periodic electrostatic focusing means extending for a plurality of periods along said path for confining said beam to-,substantially constant diameter along said path beyond said plane; said means comprising a series of apertured plate electrodes having the same inner diameter alternating along said beam path with a series of elongated annular electrodes each having a minimum inner diameter equal to said first-named inner diameter near the center and increasing to a larger diameter at each end.
  • An electron beam tube as in claim 13, comprising a velocity modulating cavity resonator coupled to said beam path near the beginning of said focusing means,
  • An electron beam tube as in claim 1, wherein said series of focusing electrodes comprises a multiplicity of identical thin apertured plates mounted close together in lalignment along said beam path, and said means further includes a D.C. voltage source connected to said plates for applying suitable potentials thereto to approximate said parabolic potential distribution at the boundary of said beam.

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US780783A 1958-12-16 1958-12-16 Periodic electrostatically focused beam tubes Expired - Lifetime US2986672A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL246440D NL246440A (US08197722-20120612-C00042.png) 1958-12-16
NL104255D NL104255C (US08197722-20120612-C00042.png) 1958-12-16
US780783A US2986672A (en) 1958-12-16 1958-12-16 Periodic electrostatically focused beam tubes
GB39543/59A GB925551A (en) 1958-12-16 1959-11-20 Periodic electrostatically focused beam tubes
FR810764A FR1240982A (fr) 1958-12-16 1959-11-20 Tubes électroniques à faisceau dirigé
DER26884A DE1264622B (de) 1958-12-16 1959-12-07 Elektrostatische Fokussierungsanordnung zur gebuendelten Fuehrung des Elektronenstrahls einer Laufzeitroehre

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US780783A US2986672A (en) 1958-12-16 1958-12-16 Periodic electrostatically focused beam tubes

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US2986672A true US2986672A (en) 1961-05-30

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FR (1) FR1240982A (US08197722-20120612-C00042.png)
GB (1) GB925551A (US08197722-20120612-C00042.png)
NL (2) NL246440A (US08197722-20120612-C00042.png)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3114072A (en) * 1960-05-31 1963-12-10 Rca Corp Electrostatically focused traveling wave tubes
US3143681A (en) * 1959-12-07 1964-08-04 Gen Electric Spiral electrostatic electron lens
US3175119A (en) * 1959-10-29 1965-03-23 Rca Corp Electrostatically focused traveling wave tube having periodically spaced loading elements
US3178653A (en) * 1960-04-04 1965-04-13 Raytheon Co Cavity resonator with beamconcentric ring electrode
US3238465A (en) * 1961-10-20 1966-03-01 Trw Inc D. c. focused and pumped parametric amplifier
US3449617A (en) * 1965-11-03 1969-06-10 Emi Ltd Electron discharge device having at least one electrode mounted by a meander-type insulator
US4754196A (en) * 1986-12-10 1988-06-28 The United States Of America As Represented By The Secretary Of The Navy Axial injection orbitron
EP3242317A4 (en) * 2014-12-31 2018-07-04 Nuctech Company Limited Electrode ring used for ion mobility spectrometer, ion migration tube and ion mobility spectrometer

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2406704B (en) 2003-09-30 2007-02-07 Ims Nanofabrication Gmbh Particle-optic electrostatic lens

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2289071A (en) * 1941-10-03 1942-07-07 Gen Electric Electron lens
US2610306A (en) * 1947-06-14 1952-09-09 Int Standard Electric Corp Velocity modulation tube
US2843793A (en) * 1953-03-30 1958-07-15 Bell Telephone Labor Inc Electrostatic focusing of electron beams

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2894170A (en) * 1955-04-28 1959-07-07 Gen Electric Electron beam amplification apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2289071A (en) * 1941-10-03 1942-07-07 Gen Electric Electron lens
US2610306A (en) * 1947-06-14 1952-09-09 Int Standard Electric Corp Velocity modulation tube
US2843793A (en) * 1953-03-30 1958-07-15 Bell Telephone Labor Inc Electrostatic focusing of electron beams

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3175119A (en) * 1959-10-29 1965-03-23 Rca Corp Electrostatically focused traveling wave tube having periodically spaced loading elements
US3143681A (en) * 1959-12-07 1964-08-04 Gen Electric Spiral electrostatic electron lens
US3178653A (en) * 1960-04-04 1965-04-13 Raytheon Co Cavity resonator with beamconcentric ring electrode
US3114072A (en) * 1960-05-31 1963-12-10 Rca Corp Electrostatically focused traveling wave tubes
US3238465A (en) * 1961-10-20 1966-03-01 Trw Inc D. c. focused and pumped parametric amplifier
US3449617A (en) * 1965-11-03 1969-06-10 Emi Ltd Electron discharge device having at least one electrode mounted by a meander-type insulator
US3484642A (en) * 1965-11-03 1969-12-16 Emi Ltd Electron discharge devices having inner and outer insulating annular projections at the gun end of the device
US4754196A (en) * 1986-12-10 1988-06-28 The United States Of America As Represented By The Secretary Of The Navy Axial injection orbitron
EP3242317A4 (en) * 2014-12-31 2018-07-04 Nuctech Company Limited Electrode ring used for ion mobility spectrometer, ion migration tube and ion mobility spectrometer

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DE1264622B (de) 1968-03-28
NL246440A (US08197722-20120612-C00042.png)
FR1240982A (fr) 1960-09-09
GB925551A (en) 1963-05-08
NL104255C (US08197722-20120612-C00042.png)

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