US3482139A - Pulse-chopped electron beam source - Google Patents

Pulse-chopped electron beam source Download PDF

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Publication number
US3482139A
US3482139A US626182A US3482139DA US3482139A US 3482139 A US3482139 A US 3482139A US 626182 A US626182 A US 626182A US 3482139D A US3482139D A US 3482139DA US 3482139 A US3482139 A US 3482139A
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United States
Prior art keywords
cavity
chopped
pulse
slot
axis
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Expired - Lifetime
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US626182A
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English (en)
Inventor
Hubert Leboutet
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
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/78—Tubes with electron stream modulated by deflection in a resonator
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
    • G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
    • G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
    • G21K1/043—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers changing time structure of beams by mechanical means, e.g. choppers, spinning filter wheels
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/08—Deviation, concentration or focusing of the beam by electric or magnetic means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns

Definitions

  • pulses emerge through this slot into a second cavity in which are also established an axial magnetic field and a transverse UHF field, and the size of said second cavity and magnitude of said fields is such that the pulses move along a convergent helical path until they are delivered through an aperture in a terminal wall of the second cavity along the common axis of both cavities.
  • This invention relates to a device for converting a continuous electron beam into a pulse-chopped beam.
  • a device of this kind known in the prior art, is described in the French Patent No. 1,024,850 and provides a pulse-chopped electron beam from a continuous beam injected along the axis of a cavity in which there exists a uniform axial magnetic field and a transverse high frequency electric field.
  • the high frequency therein is suitably chosen with respect to the magnetic field so that the electrons are caused to rotate at the cyclotron frequency and describe a helical trajectory whose radius gradually sively increases as the electrons propagate forward in the axial direction.
  • a terminal wall or plate which intercepts the electron beam so that the electrons move on the surface of the plate along a closed trajectory which may be circular or elliptical.
  • the plate is provided with one or more radial slots which intersect the closed electron trajectory and permit the passage therethrough of a pulse-chopped electron beam, while the electrons impinging onto the plate outside the slots are absorbed therein. In this Way there are obtained electron pulses emerging from the cavity and distributed on a cylindrical surface having the same axis as the initial continuous beam, but in such a device no pulse emerges along the axis itself.
  • the known provides a pulse-chopped beam at the output thereof, the resulting pulses are displaced from the axis of the device.
  • Such displacement is clearly disadvantageous, especially where the pulse-chopped beam is to be used for example, in conjunction with an accelerator device requiring an injection along a particular trajectory with consistent accuracy.
  • the present invention consists of a device for converting a continuous electron beam into a pulse-chopped beam, comprising a first cavity in which said continuous beam is propagated along a divergent helical path about the axis of the cavity under the combined action of an axial magnetic field and a transverse high frequency elec- 3,482,139 Patented Dec.
  • the cavity having a terminal wall provided with one or more apertures through which discontinuous groups of electrons emerge from the cavity at a distance from the cavity axis, wherein the discontinuous electron groups are caused to propagate along a convergent helical path in a second cavity, adjacent the first one, under the combined action of an axial magnetic field and a trans verse high frequency electric field similar to those prevailing in the first cavity, said second cavity having a terminal wall provided with an aperture aligned with the cavity axis for the outlet of the beam.
  • the primary object of the present invention is to provide a device for converting a continuous electron beam into a pulse-chopped beam which entirely eliminates, or otherwise materially avoids, the disadvantages inherent in known devices of a similar nature.
  • Another object of the invention is to provide in the device slots of an improved shape in the terminal plate of the cavity in order to obtain certain special effects.
  • a further object of the invention is to provide the terminal plate of the cavity with a slot of a shape that enables alternatively either a chopped or a continuous beam to be obtained.
  • FIGURE 1 is a longitudinal section through a device in accordance with the invention.
  • FIGURE 2 is a cross-sectinon through the device of FIGURE 1;
  • FIGURES 3 and 4 represent two different embodiments of the slot 7 for use in the device of FIGURES 1 and 2;
  • FIGURE 5 shows an alternative embodiment in which the terminal partition plate 6 of the device of FIGURES 1 and 2 is replaced by a baflle;
  • FIGURES 6 and 7 show two different modifications to the battle of FIGURE 5;
  • FIGURE 8 shows a modification of FIGURE 2
  • FIGURE 9 shows a modification of FIGURE 3.
  • FIGURE 10 shows a modification of FIGURE 4.
  • FIGURE 11 shows a modification of FIGURE 5.
  • FIGURE 1 shows a device in which a continuous electron beam 1, issuing from an electron gun 2, enters with a speed v into a cavity 3, in which there is established by any conventional means (not shown) a uniform axial magnetic field of intensity B, while a high frequency source 4 of frequency f establishes in the same cavity a mode having a transverse high frequency electric component. Under these conditions the electrons propagate in cavity 3 along helical trajectories describing spirals of a progressively increasing diameter so that the spirals are contained within a cone 5.
  • the cyclotron frequency F of the electron rotation is related to the field intensity B by the formula:
  • F being in megacycles/sec. if B is expressed in gauss;
  • 3 M is the relativistic mass of the electrons and M their mass at rest.
  • the cavity 3 is closed by a partition plate 6, provided with at least one radial slot 7, having, for example, the sectoral shape represented in FIGURE 2.
  • the electrons arriving at the plate 6 sweep this plate along a circle 8 whose diameter depends upon the values of the field B, the length l, the energy supplied by source 4, and the initial velocity v.
  • the slot 7 is disposed so as to interrupt the circle 8.
  • a series of pulses 9 each having an electrical length equal to the sectoral angle of slot 7.
  • these pulses emerge from slot 7 outside of, i.e., displaced from, the axis of cavity 3.
  • a second cavity 10 is disposed adjacent the first cavity 3.
  • the second cavity is given the same geometrical dimensions as the first one, and there are established in cavity 10 the same axial magnetic field l3 and the same transverse high frequency electric field component as in cavity 3, use being made preferably, but not necessarily, of the same high frequency source 4 providing frequency f.
  • This pulse-chopped beam may therefore be utilized in an accelerator.
  • the frequency f of source 4 is chosen from the values that satisfy either of the following two equations:
  • Equation 2 is used when it is desired to obtain a phase shift 1r between homologous points of the two cavities; then the numbers In and n are given values such that F/ be positive (condition 2m n).
  • Equation 3 is utilized when it is desired to have a zero phase shift at homologous points of the two cavities.
  • the source of frequency f excites in the cavity a wave whose wave length when propagating in an infinite wave guide having the same external sizes as the cavity is Ag.
  • This wave length is related to the length l of the cavity by the relation M1 2 where q is a certain integer. This number can consequently be determined from Equation 4 after kg has been measured.
  • the radial position and the length of slot 7 are chosen in such a manner that this slot intersects the circle 8 of radius r on the partition plate 6, which circle is swept d by the beam.
  • the radius 4 depends on the field B and on the length l as well as on the frequency f and the energy of source 4. Thus the radius r may be varied, if desired, by varying the energy.
  • FIGURES 3, 4, 5 represent some possible embodiments providing a different shape slot 7 than provided in FIGURE 2.
  • slot 7 has the form of a V having its opening towards the axis of the device. The use of this shape is to permit a reduction of the beam current when the energy of source 4 increases. Indeed, as a result of an increase of radius r, due to an increase of energy, the slot width swept by the beam decreases and consequently the chopped pulses become shorter and the mean current is reduced.
  • FIGURE 4 is distinguished from FIGURE 3 by the fact that the sides of the V are curvilinear. With this disposition, the phase of the pulses is shifted in one or the other direction depending on the sense of rotation of the beam on circle 8. This phase variation follows a desired law, determined by the shape of the curvilinear sides of the slot, and at the same time the length of the chopped pulse varies with the energy applied.
  • FIGURE 5 the partition plate 6 of FIGURES 1 and 2 is replaced by a baffie 13 whose edge 14 extends in the plane passing through the axis of the cavity which is supposed here to be rectangular. This case may be considered as that of slot 7 of FIGURE 2 in which the sector angle has been increased to Then the beam sweeping the circle 8 is chopped into pulses each of which has a duration equal to the interval between two consecutive pulses.
  • the battle, replacing the partition plate, is advantageous when it is desired to achieve a strong coupling between the cavities 3 and 10.
  • FIGURES 8 through 11 show modifications of the embodiments of FIGURES 2 to 5, respectively.
  • the radial slot 7 of FIGURES 2, 3 or 4, or the baflle 13 of FIGURE 5 are combined with a small axial hole 16 of radius r sufficient to permit the passage of an axial beam having substantially the same diameter as the inlet beam 1.
  • This combination provides, in particular, in FIGURE 8 the familiar key-hole shape, while in FIGURE 11 a simple semi-circular notch is pro- 'vided in bafile 13. This disposition makes it possible to obtain, at the outlet of the hole 12.
  • cavity 10 should be supplied by the same high frequency source as cavity 3.
  • two different sources may be employed with slightly different frequencies.
  • the phase of a pulse 9 in cavity 10 slowly shifts with respect to the phase of the outlet at the slot 7. Then only a portion of pulse 9 arrives at the outlet 12 at the suitable phase for emerging and the remainder is lost in the terminal wall of cavity 10. This provides an additional means for shortening the pulse 9.
  • a device for converting a continuous electron beam into a pulse-chopped beam comprising a pair of adjacent cavity resonators separated by a wall provided with at least one aperture displaced from the common axis of said cavities, means for injecting along the axis of one of said cavities a continuous electron beam, means for establishing in both of said cavities a common axial magnetic field and a transverse high frequency electric field whereby said beam is propagated within said first cavity along a divergent helical path along said axis until said beam strikes said wall along a path of rotation, said aperture in said separating wall being disposed on said path of rotation so that said beam is chopped into discontinuous pulses of electrons while sweeping across said aperture, the size of said second cavity and magnitude of said fields therein being such that said discontinuous pulses emerging from said aperture into said second cavity propagate therein along a convergent helical path terminating on said common axis, and a terminal wall of said second cavity provided with an aperture aligned with said common axis for the outlet of said pulses
  • a device as claimed in claim 1, comprising means for exciting in both cavities high frequency fields at the same frequency.
  • a device as claimed in claim 1, wherein said aperture in said separating wall between cavities is a slot in the form of a V opened toward said common axis.
  • said separating wall is a baffie whose edge comprises a point at said common axis.
  • said aperture in said separating wall is a sectoral slot combined with a circular hole in registry with said common axis, thereby forming a key-hole shaped aperture.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Particle Accelerators (AREA)
US626182A 1966-03-31 1967-03-27 Pulse-chopped electron beam source Expired - Lifetime US3482139A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR55771A FR1482099A (fr) 1966-03-31 1966-03-31 Perfectionnements aux sources de faisceau haché en impulsions

Publications (1)

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US3482139A true US3482139A (en) 1969-12-02

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US (1) US3482139A (pm)
BE (1) BE695188A (pm)
CH (1) CH469347A (pm)
DE (1) DE1589589A1 (pm)
FR (1) FR1482099A (pm)
GB (1) GB1159512A (pm)
NL (1) NL6704658A (pm)
SE (1) SE337632B (pm)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4068146A (en) * 1976-05-17 1978-01-10 Atomic Energy Of Canada Limited Charged particle beam deflector
US4629937A (en) * 1984-02-02 1986-12-16 California Institute Of Technology Compact electron gun for emitting high current short duration pulses
US4656430A (en) * 1984-03-16 1987-04-07 The United States Of America As Represented By The United States Department Of Energy Short rise time intense electron beam generator

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2870368A (en) * 1953-07-14 1959-01-20 Rca Corp Electron beam tubes

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2870368A (en) * 1953-07-14 1959-01-20 Rca Corp Electron beam tubes

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4068146A (en) * 1976-05-17 1978-01-10 Atomic Energy Of Canada Limited Charged particle beam deflector
US4629937A (en) * 1984-02-02 1986-12-16 California Institute Of Technology Compact electron gun for emitting high current short duration pulses
US4656430A (en) * 1984-03-16 1987-04-07 The United States Of America As Represented By The United States Department Of Energy Short rise time intense electron beam generator

Also Published As

Publication number Publication date
GB1159512A (en) 1969-07-30
CH469347A (fr) 1969-02-28
FR1482099A (fr) 1967-05-26
DE1589589A1 (de) 1970-04-16
SE337632B (pm) 1971-08-16
BE695188A (pm) 1967-08-14
NL6704658A (pm) 1967-10-02

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