Classifications

• • 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
• • 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
  • H05H7/14—Vacuum chambers
  • H05H7/18—Cavities; Resonators
• • 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
  • H05H13/00—Magnetic resonance accelerators; Cyclotrons
  • H05H13/10—Accelerators comprising one or more linear accelerating sections and bending magnets or the like to return the charged particles in a trajectory parallel to the first accelerating section, e.g. microtrons or rhodotrons
• • 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

Definitions

• the present invention relates to an electron accelerator. It finds an application in the irradiation of various substances such as agro-food products, either directly by electrons, or by X-rays obtained by conversion on a heavy metal target.
• An electron accelerator which generally comprises a resonant cavity supplied by a high frequency field source, and an electron source capable of injecting electrons into the cavity. If certain phase and speed conditions are satisfied, the electrons are accelerated by the electric field throughout their passage through the cavity.
• the electron beam crosses the cavity several times.
• the device then includes an electron deflector receiving the accelerated beam for the first time, deflecting it by around 180 ° and reinjecting it into the cavity for a new acceleration.
• a second deflector can again deflect the beam which has undergone two accelerations, to make it cross a third time the cavity and thus obtain a third acceleration, and so on.
• Such a device is described, for example, in French patent No. 1,555,723 entitled "100 MeV electron accelerator in steady state".
• This type of accelerator has the following disadvantage.
• the electron beam follows a path and coincides with the axis of the latter.
• the electric field has only one component which is directed along the axis.
• the electron beam follows a path which is no longer directed along the axis.
• a magnetic component perpendicular to the axial component of the electric field can act on the electron beam. This action will result in a deflection of the electrons.
• This deviation will depend on the phase of the electromagnetic field, which will produce a scattering of the beam, some of which will consequently be lost on the walls of the cavity.
• this parasitic phenomenon is amplified during multiple crossings.
• the electron beam is returned on itself and thus goes back and forth along the axis of the cavity.
• the electron beam always follows, during its multiple crossings, a path for which the deflecting fields are zero (the electric field is parallel to the speed vector of the electrons, and in opposite directions).
• these two devices are complex to implement: in the first, the various trajectories of the electrons do have a common branch merged with the axis of the cavity, but the other branches are external to the cavity, which increases the complexity and the size of the device.
• the object of the present invention is precisely to remedy these drawbacks. To this end, it offers an electron accelerator which uses a cavity whose original shape, in this application makes it possible to benefit from the effects of multiple crossings while retaining the condition stated above on the absence of deflecting fields along the paths taken by the electrons.
• the present invention relates to an electron accelerator of the multiple acceleration type mentioned above and which is characterized in that the resonant cavity is a coaxial cavity resonating according to the fundamental mode, with an external conductor and a inner conductor having the same axis, the electron beam being injected into this cavity in the median plane perpendicular to the axis and along a first diameter of the outer conductor, the electron deflector keeping the electrons in the median plane and reinjecting the beam in the cavity always in the median plane and along a second diameter of the external conductor, etc. the outer conductor and the inner conductor being pierced with diametrically opposite openings taken by the beam during its successive crossings of the cavity.
• FIG. 1 shows a coaxial cavity resonating according to the fundamental mode
• Figure 2 illustrates a property of the coaxial cavity relating to the absence of magnetic field in the median plane of the cavity
• Figure 3 shows, in section, an electron accelerator according to the invention
• Figure 4 illustrates geometric characteristics of the device of the invention
• FIG. 5 shows an alternative embodiment of the invention, intended to reduce ohmic losses.
• a coaxial cavity CC is seen, constituted by an external cylindrical conductor 10, an internal cylindrical conductor 20 and two flanges 31 and 32.
• a cavity has an axis A and a median plane Pm, perpendicular to the axis.
• fundamental of electric transverse type, for which the electric field E is purely radial in the median plane and decreases on both sides of this plane. to cancel on the flanges 31, 32.
• the magnetic field is maximum along the flanges and is canceled in the median plane by changing direction.
• Such a mode can be designated, according to conventional conventions, by TE 001 , the initials TE recalling that it is a mode where the electric field is transverse, where the first index "0" indicates that the field has the symmetry of revolution, the second index "0" indicates that there is no field cancellation along a radius of the cavity, and the third index of value 1 indicates that there is a half alternation of the field in a direction parallel to the axis.
• Such a cavity can be supplied by a high frequency SHF source coupled to the cavity by a loop 34.
• the electron beam is injected into the coaxial cavity in the median plane thereof. It is indeed in this plane that there is no parasitic field capable of deflecting the beam. As this point is essential we can stop there.
• the cavity is seen in cross section in the median plane.
• the electric fields E1 and E2 are equal along two distinct radii.
• a contour 17 is defined by these two radii and by two arcs of a circle along which the electric field is radial.
• the circulation of the electric field (that is to say the integral of this field) is zero along this contour. Consequently, the flux of magnetic induction through a surface resting on this contour is also zero. In other words, there is no magnetic component perpendicular to the median plane.
• FIG. 3 shows, schematically, a complete accelerator according to the invention.
• the device comprises an electron source S, a coaxial cavity CC, formed of an outer cylindrical conductor 10 and an inner cylindrical conductor 20, two electron deflectors D1 and D2.
• the operation of this device is as follows.
• the electron source S emits a beam of electrons Fe directed in the median plane of the coaxial cavity CC represented in section (the plane of the figure being the median plane).
• the beam enters the cavity through an opening 11. It crosses the cavity along a first diameter d1 of the external conductor.
• the inner conductor 20 is pierced with two diametrically opposite openings 21 and 22.
• the electron beam is accelerated by the electric field if the phase and frequency conditions are satisfied (the electric field must remain in the opposite direction to the speed of the electrons).
• the accelerated beam leaves the cavity through an opening 12 diametrically opposite to the opening 11. It is then deflected by a deflector D1.
• the beam is reintroduced into the coaxial cavity through an opening 13. It then borrows a second diameter d2 and undergoes a second acceleration in the cavity. It comes out through the opening 14. On its exit, the beam is again deflected by a deflector D2 then reintroduced into the cavity by an opening 15. It borrows a third diameter d3 and undergoes a third acceleration, etc.
• the coaxial nature of the acceleration structure means that the electric field does not have the same direction in the first and in the second half of the path taken by the electrons in the cavity, in other words along the radius which goes from the external conductor. to the inner conductor, then along the radius from the inner conductor to the outer conductor.
• the spatial variation of the field is accompanied by a temporal variation since the field has a high frequency (a few hundred megahertz).
• k 1
• the radius of curvature in one of the deflectors is designated by Rc and by Ra the distance between the axis of the cavity and the inlet eD or the outlet sD of this deflector. These quantities are illustrated in FIG. 4. Furthermore, the angle between two paths is equal to ⁇ / 2n. So we have the following relationships:
• Ra 111 cm
• Rc 22.1 cm
• the external radius R2 delimiting the field of the cavity must obviously be less than Rc to take account of the thickness of the wall and possibly allow it to be housed between it and the deflector of the auxiliary focusing devices.
• the dimensions calculated above are compatible with these practical requirements.
• the electrical quality of an accelerating cavity is conventionally characterized by its efficient shunt impedance
• the shunt impedances obtained in practice are somewhat lower than the theoretical values, and in fact the dissipated power will be close to 350 kW.
• the impedance-shunt, for homothetic cavities, is proportional to the root of the wavelength. A cavity operating at 700 MHz increasing the energy of the electrons
• the radii of the cavity would differ somewhat, but the impedance-shunt would vary little, and as a first approximation the dissipated power would vary in a manner inversely proportional to the number of passages.
• the ohmic losses due to the currents flowing in the flanges of the cavity can be reduced by modifying the shape of the internal conductor, as illustrated in FIG. 5.
• the internal conductor 20 ends in two frustoconical parts 33 and 35.
• the inductance of the cavity is reduced. To keep the same frequency, you need to increase the capacitance, so lengthen the cavity a little.
• the inventors have demonstrated a considerable reduction in the transverse dimensions of the beam and a less great sensitivity to misadjustments by using deflection magnets whose faces, at the entrance and at the exit of the beam, are tangent. to a corner dihedral at the apex close to ⁇ (1- (1 / 2n)) if n is the number of beam crossings of the cavity.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Particle Accelerators (AREA)

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Cited By (5)

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Family Cites Families (4)

• 1987
  • 1987-05-26 FR FR8707378A patent/FR2616032B1/fr not_active Expired
• 1988
  • 1988-05-19 IL IL86448A patent/IL86448A/xx not_active IP Right Cessation
  • 1988-05-25 DE DE88904976T patent/DE3880681T2/de not_active Expired - Lifetime
  • 1988-05-25 AU AU19437/88A patent/AU613381B2/en not_active Expired
  • 1988-05-25 WO PCT/FR1988/000262 patent/WO1988009597A1/fr active IP Right Grant
  • 1988-05-25 ES ES8801643A patent/ES2007889A6/es not_active Expired
  • 1988-05-25 JP JP63504622A patent/JP2587281B2/ja not_active Expired - Lifetime
  • 1988-05-25 CA CA000567653A patent/CA1306075C/fr not_active Expired - Lifetime
  • 1988-05-25 US US07/449,955 patent/US5107221A/en not_active Expired - Lifetime
  • 1988-05-25 EP EP88904976A patent/EP0359774B1/de not_active Expired - Lifetime
• 1989
  • 1989-01-18 KR KR89700094A patent/KR960014439B1/ko not_active IP Right Cessation

Non-Patent Citations (1)

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