US3454818A - Apparatus for shortening of electron pulses emitted from an electron gun - Google Patents

Apparatus for shortening of electron pulses emitted from an electron gun Download PDF

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Publication number
US3454818A
US3454818A US576904A US3454818DA US3454818A US 3454818 A US3454818 A US 3454818A US 576904 A US576904 A US 576904A US 3454818D A US3454818D A US 3454818DA US 3454818 A US3454818 A US 3454818A
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frequency
electron
bursts
wave
buncher
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US576904A
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English (en)
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Jacques Soffer
Jean Paul Mangin
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Thales SA
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CSF Compagnie Generale de Telegraphie sans Fil SA
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H9/00—Linear accelerators
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/08—Arrangements for injecting particles into orbits

Definitions

  • This invention relates in general to electron discharge devices, and more particularly to apparatus for generating electron pulses of extremely short duration emitted from an electron gun for injection into a device Where such pulses are extremely desirable such as an accelerator for example.
  • a pulse length of this order of magnitude cannot be attained directly by applying a pulse shaped control onto the control electrode of the electron gun since the time constant of the capacitive grid-cathode circuit limits the minimum practicable pulse length to the order of 6 nanoseconds. Moreover, if high intensities are to be obtained without applying high voltages to the gun electrodes, it is preferred to operate above this limit and not to reduce the pulse length below about 10 ⁇ to l2 nanoseconds.
  • the present invention consists of an apparatus for shortening electron pulses emitted from an electron gun controlled by a signal having a repetition frequency f, including a buncher device positioned on the path of the electron stream for converting each pulse generated by the electron gun into a series of electron bursts, and further includes a debuncher device positioned adjacent the buncher device for subsequently causing the electron bursts formed by the buncher to interact with a high frequency wave in such a manner that some bursts of each series drift with respect to the waveto a greater extent than other bursts of the same series, whereby the bursts are debunched and regrouped so as to form a nal pulse having a duration shorter than the initial one generated by the electron gun.
  • FIGURE 1 represents schematically one form of apparatus according to the present invention
  • FIGURE 2 is an explanatory diagram relating to the apparatus of FIG. l;
  • FIGURE 3 shows the apparatus of FIGURE 1 used for electron injection in a linear accelerator
  • FIGURE 4 represents schematically an alternative form of apparatus according to the present invention.
  • FIGURE 5 is an explanatory diagram relating to the apparatus of FIG. 4.
  • FIGURE l schematically shows apparatus which includes an electron gun 1 emitting a beam of electrons which propagate along the dotted axis 2.
  • bunching device 4 adapted to produce a series of electron bursts, which device 4 is formed by a chain of p resonator cavities uniformly spaced apart and excited at a frequency f1 by a signal source 5. Thereafter, there is provided guide portion 6 excited at a frequency f2 by a signal source 7 having an energy that is not suicient to accelerate the electrons by means of the phenomenon of trapping the electron bursts by a xed phase of the wave.
  • An adjustable phase shifter 9 is interposed between the elements S and 5 for purposes to be more fully described hereinafter.
  • This apparatus of the invention operates in the following manner:
  • the diagram a represents, as a function of time, a pulse of duration T, emitted from the gun 1 and entering the buncher device 4 (point a in FIGURE l).
  • the electrons contained in the pulse interact with the wave of frequency f1 whose curve is represented by diagram b.
  • the electrons ar-e bunched or grouped in a series of bursts p represented in diagram c.
  • This series occupies substantially the same total duration T as the initial pulse, and the width s of each burst corresponds approximately to 20 of the phase variaaimais E tion of the wave f1.
  • This series of bursts enters at c (FIG' URE l) in the guide 6.
  • the first burst p1 enters the guide 6 when the phase of wave f2 is B, lagging by a phase angle a1 behind the wave peak, whereas the last burst pn enters the guide 6 when the phase of wave f2 is C, leading by a phase angle a2 ahead of the wave peak.
  • the same conditions are maintained on all consecutiVe pulses, i.e., the phase shift between corresponding bursts on either side of the center burst is equal to the absolute Vahle of the sum of the individual input phases of the respective burst.
  • the wave f2 propagates without delay, that is at the speed of light, while the electrons have 'been subjected to relatively little acceleration within the buncher 4 and consequently propagate at a considerably lower speed. Moreover, the bursts cannot be trapped by the wave because the energy of the wave is insufficient to initiate this phenomenon. The bursts will therefore lag with respect to the wave.
  • the bursts such as p1, which lag behind the wave and the bursts, such as pn, which lead the wave, behave in different manners.
  • the two groups are at the beginning in the accelerating field corresponding to the positive portions of curve f2.
  • the burst p1 attains the negative portion of the curve f2, corresponding to the decelerating field, after a drift along the short Wave portion BD, corresponding to the phase angle l
  • the burst pn attains the negative portion of the curve, that is, the decelerating field, after a much longer drift along the wave portion CE, corresponding to the phase angle ,B2 which is much greater than the angle l, as seen in the diagram.
  • burst pn remains in the accelerating field longer than the burst p1.
  • bursts such as p,n therefore acquire in the guide a mean velocity which is higher than that of the bursts such as p1, and the former catch up with the latter during their propagation.
  • the bunching of the bursts is destroyed and the electrons join again to form a continuous pulse at the output e of the guide (FIGURE 1) which acts as a debuncher.
  • This pulse represented in the dia-gram e of FIGURE 2, has a duration T shorter than the initial duration T.
  • the initial duration of l2 nanoseconds is thus reduced to about 2.5 nanoseconds.
  • FIGURE 3 in which the same reference numerals as in FIGURE 1 designate the corresponding elements, represent-s schematically an application of the apparatus of FIGURE 1 for injecting electrons into a linear accelerator.
  • the shortened pulses issued from guide 6 enter a preliminary conventional buncher 10 wherein the pulse is bunched into groups or bursts. Then the bursts enter the accelerating section 11, constructed in conventional manner for accelerating the electrons to a speed nearly equal to the speed of light and giving them high energy. If necessary, the accelerated bursts issued from section 11 may be -grouped into a shortened group with the aid of a regrouper device 12 such as the one described in our copending U.S. patent application Ser. No. 438,656, -filed Mar. l0, 1965. The electrons issued from the regrouper 12 or directly from accelerator 11 are directed toward a device for their use, not shown.
  • the block 1 represents, as in FIGURE 1, an electron gun emitting electrons that propagate along the dotted axis 2.
  • the electrons are emitted in pulses having a length of the order of l2 nanoseconds at a repetition frequency f of the order of a few kilocycles/sec.
  • a buncher 14 excited at a frequency f4 for example of the order of 3000 rnc/sec., supplied by a source 15 which is deeply a-mplitude modulated at a frequency F, for example, of the order of 20 mc./sec.
  • the buncher 14 extends into an accelerating guide 17, in which the modulated wave propagates with a constant (phase velocity nearly equal to that of light.
  • the electrons are injected, for example, into a high energy accelerator 118, analogous to block 11 of FIGURE 3, and excited by a HF source 19.
  • This apparatus in accordance with the invention, as illustrated in FIGURE 4, operates as follows:
  • the modulating magnitude supplied by source 15 is such that the energy exciting the buncher varies sinusoidally at the frequency f4, amplitude modulated at frequency F.
  • This energy produces a field which varies sinusoidally in the space between zero and a peak value.
  • This sinusoidal distribution of period vg/F propagates in the buncher with a group velocity vg. If the length of the buncher is equal to half a period of the spatial distribution, the field along the buncher Varies periodically in time between two spatial distributions, one of which is represented by the curve A and the other by the curve B in FIGURE 5, which provides a field which is a function of the axial coordinate of the buncher.
  • the electrons which enter the buncher during the the field has the distribution A meet from the beginning a weak field so that they are accelerated relatively little and leave the buncher with a relatively low mean velocity.
  • the electrons which enter the buncher during the distribution B encounter during their entire passage through the buncher a relatively intense field which gives them a strong acceleration and a relatively high mean velocity. These electrons group themselves into bursts near the peak of the wave (phase 1r), while the preceding ones group themselves into bursts near the phase vr/ 2.
  • the electrons issuing from the first half of the initial pulse arrive during the field distribution A and those of the second half arrive during the field distribution B.
  • the modulation of source need not be carried out sinusoidally; it suffices to modulate the duration or position of the pulses such that the output power of the source 1S varies as an arc of a sinusoid just for the duration of the pulse issuing from the electron gun.
  • An apparatus for shortening the length of electron pulses of duration T emitted from an electron gun with a repetition frequency f comprising buncher means positioned along the path of the electrons for converting each pulse into a series of individual electron bursts, each series having a duration T, and debuncher means positioned along said path subsequent to said buncher means in the direction of said electron emission for grouping the individual electron bursts in each series including means for effecting interaction between the electron bursts and a high frequency wave of frequency f2 in such a manner that some bursts of each series drift with respect to the wave to a greater extent than other bursts of the same series, whereby the bursts are debunched and regrouped so as to form a final pulse having a duration T' shorter than the initial duration T.
  • Apparatus as claimed in claim 2 further including mixing means for producing the frequency f1, as the sum beat frequency obtained by mixing the frequencies mf and f2.
  • Apparatus as claimed in claim 4 further including means connected to said mixing means for adjusting the phase of the wave of frequency mf to provide a beat node of the frequencies f1 and f2 at the center of each series of electron bursts.
  • Apparatus for producing pulses of electrons having an extremely short duration comprising electron beam generating means for generating a stream of electrons along a given path, modulating means applying a control signal of frequency f to said beam generating means for modulating said stream of electrons into a plurality of pulses of duration T, buncher means positioned along said path for converting each pulse of electrons into a series of individual electron bursts, each series having a duration T, and debuncher means positioned along said path subsequent to said buncher means lfor causing some bursts of each series to drift with respect to other bursts of said series toward a common point of the series, whereby the bursts are regrouped to form a final pulse having a duration T shorter than duration T.
  • said buncher means includes signal means for effecting interaction between said pulses of duration T and a high frequency wave of frequency f1, equal to mf plus a frequency f2, where m is an integer and mf is very small in comparison with f2.
  • said signal means includes multiplier means connected to said modulating means for generating a signal having a frequency mf, generator means for generating a signal having a frequency f2, and mixing means for adding the signal outputs from said multiplier means and said generator means for producing a signal having a frequency f1, said buncher device further including a chain of resonator cavities through which said electrons pass, which cavities are excited by said signal of frequency f1.
  • said debuncher means includes a waveguide excited by said signal of frequency f2 and within which said electrons interact with a wave of frequency f2.
  • phase shifting means connected between said multiplier means and said mixing means for providing a phase shift between the phases of the first and last bursts of a series entering said waveguide with respect to the wave of frequency f2.
  • phase shift is equal to 21rmf1 ⁇ .

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)
US576904A 1965-09-03 1966-09-02 Apparatus for shortening of electron pulses emitted from an electron gun Expired - Lifetime US3454818A (en)

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Application Number Priority Date Filing Date Title
FR30331A FR1455407A (fr) 1965-09-03 1965-09-03 Dispositifs de raccourcissement pour les impulsions issues d'un canon à électrons

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US3454818A true US3454818A (en) 1969-07-08

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US (1) US3454818A (xx)
BE (1) BE685128A (xx)
CH (1) CH462242A (xx)
DE (1) DE1273708B (xx)
FR (1) FR1455407A (xx)
GB (1) GB1143200A (xx)
NL (1) NL6612398A (xx)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3784873A (en) * 1970-10-30 1974-01-08 Thomson Csf Device for bunching the particles of a beam, and linear accelerator comprising said device
US4641103A (en) * 1984-07-19 1987-02-03 John M. J. Madey Microwave electron gun
US5506473A (en) * 1990-06-15 1996-04-09 Thomson-Csf Electron gun for providing electrons grouped in short pulses
US7116064B1 (en) * 2004-02-27 2006-10-03 Advanced Energy Systems, Inc. Axisymmetric emittance-compensated electron gun
FR3000291A1 (fr) * 2012-12-26 2014-06-27 Thales Sa Procede de controle du profil temporel de vitesses d'un faisceau d'electrons

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3070726A (en) * 1959-06-05 1962-12-25 Kenneth B Mallory Particle accelerator
US3333142A (en) * 1962-03-22 1967-07-25 Hitachi Ltd Charged particles accelerator

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2813996A (en) * 1954-12-16 1957-11-19 Univ Leland Stanford Junior Bunching means for particle accelerators
GB815063A (en) * 1955-02-17 1959-06-17 Vickers Electrical Co Ltd Improvements relating to linear electron accelerators

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3070726A (en) * 1959-06-05 1962-12-25 Kenneth B Mallory Particle accelerator
US3333142A (en) * 1962-03-22 1967-07-25 Hitachi Ltd Charged particles accelerator

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3784873A (en) * 1970-10-30 1974-01-08 Thomson Csf Device for bunching the particles of a beam, and linear accelerator comprising said device
US4641103A (en) * 1984-07-19 1987-02-03 John M. J. Madey Microwave electron gun
US5506473A (en) * 1990-06-15 1996-04-09 Thomson-Csf Electron gun for providing electrons grouped in short pulses
DE4119517C2 (de) * 1990-06-15 2002-09-19 Thomson Csf Elektronenkanone zur Erzeugung von in kurzen Impulsen gruppierten Elektronen
US7116064B1 (en) * 2004-02-27 2006-10-03 Advanced Energy Systems, Inc. Axisymmetric emittance-compensated electron gun
FR3000291A1 (fr) * 2012-12-26 2014-06-27 Thales Sa Procede de controle du profil temporel de vitesses d'un faisceau d'electrons
EP2750485A1 (fr) * 2012-12-26 2014-07-02 Thales Procédé de controle du profil temporel de vitesses d'un faisceau d'electrons

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DE1273708B (de) 1968-07-25
GB1143200A (en) 1969-02-19
NL6612398A (xx) 1967-03-06
FR1455407A (fr) 1966-04-01
BE685128A (xx) 1967-01-16
CH462242A (fr) 1968-09-15

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