Vario-energy electron accelerator

Patent metadata

Field	Value
Publication number	US-10743401-B2
Application number	US-201916698149-A
Country	US
Kind code	B2
Filing date	Nov 27, 2019
Priority date	Nov 28, 2018
Publication date	Aug 11, 2020
Grant date	Aug 11, 2020

Abstract

A vario-energy electron accelerator includes a resonant cavity consisting of a closed conductor, an electron source injecting a beam of electrons into the resonant cavity, an RF system coupled to the resonant cavity and generating an electric field in the resonant cavity, magnet units centred on a mid-plane and generating a field in a deflecting chamber in fluid communication with the resonant cavity, the magnetic field deflecting along a first deflecting trajectory of adding length an electron beam exiting the resonant cavity along a first radial trajectory to reintroduce it into the resonant cavity along a second radial trajectory, an outlet for extracting along an extraction path an accelerated electron beam from the resonant cavity towards a target, wherein at least one of the magnet units is adapted for modifying the first deflecting trajectory to a second deflecting trajectory, allowing a variation of the energy of the electron beam.

First claim

The invention claimed is:

1. An electron accelerator comprising:
a resonant cavity consisting of a hollow closed conductor comprising:
an outer wall comprising an outer cylindrical portion having a central axis, Zc, and having an inner surface forming an outer conductor section, and,
an inner wall enclosed within the outer wall and comprising an inner cylindrical portion of central axis, Zc, and having an outer surface forming an inner conductor section,
wherein the resonant cavity is symmetrical with respect to a mid-plane, Pm, normal to the central axis, Zc,

an electron source configured for radially injecting a beam of electrons into the resonant cavity, from an introduction inlet opening on the outer conductor section to the central axis, Zc, along the mid-plane, Pm,
an RF system coupled to the resonant cavity and configured for generating an electric field, E, between the outer conductor section and the inner conductor section, oscillating at a frequency, f RF , to change the velocity of the electrons of the electron beam along radial trajectories in the mid-plane, Pm, extending from the outer conductor section towards the inner conductor section and from the inner conductor section towards the outer conductor section,
N magnet units, with N>1 and N∈ , each one of the N magnet units being centered on the mid-plane, Pm, and comprising a set of deflecting magnets configured for generating a magnetic field in a deflecting chamber in fluid communication with the resonant cavity by a cavity outlet aperture and a cavity inlet aperture, the magnetic field being configured for:
deflecting an electron beam entering into the deflecting chamber through the cavity outlet aperture at the end of a first radial trajectory in the resonant cavity along the mid-plane, Pm, over a first deflecting trajectory having an adding length, said first deflecting trajectory extending from the cavity outlet aperture to the cavity inlet aperture, through which the electron beam is re-introduced into the resonant cavity towards the central axis along a second radial trajectory in the mid-plane, Pm, the second radial trajectory being different from the first radial trajectory, wherein
the adding length is such that when the electron beam is re-introduced into the resonant cavity, the RF system is synchronized for applying an electric field for accelerating the electron beam along the second radial trajectory, and

an outlet for extracting an accelerated electron beam of energy, W, from the resonant cavity towards a target,

wherein at least one of the N magnet units is a vario-magnet unit configured for modifying the corresponding first deflecting trajectory to a second deflecting trajectory of second length different from the adding length thus allowing a variation of an energy, W, of the accelerated electron beam extracted from the outlet.

2. The electron accelerator according to claim 1 , wherein the second length is such that when the electron beam is re-introduced into the resonant cavity, the RF system is synchronized for applying an electric field for decelerating the electron beam along the second radial trajectory.

3. The electron accelerator according to claim 1 , wherein the at least one vario-magnet unit comprises,
a first set of magnets centered on the mid-plane, Pm, located at a first radial distance from the central axis, Zc, and configured for deflecting the electron beam along a deflecting trajectory of adding length, L+, wherein the first set of magnets can be activated or deactivated to generate or not a magnetic field in the corresponding deflecting chamber, and
a second set of magnets centered on the mid plane, Pm, radially aligned with the first set of magnets and located at a second radial distance from the central axis, Zc, which is larger than the first radial distance.

4. The electron accelerator according to claim 3 , wherein the first and second set of magnets are configured for generating a magnetic field,
in a single deflecting chamber common to both sets of magnets.

5. The electron accelerator according to claim 1 , wherein the at least one vario-magnet unit comprises moving means for discretely or continuously moving radially the at least one vario-magnet units back and forth along a bisecting direction parallel to a bisector of the angle formed by the first and second radial trajectories at the central axis, Zc, and thus discretely or continuously varying the energy, W, of the accelerated electron beam extracted from the outlet.

6. The electron accelerator according to claim 5 , wherein the moving means comprise a motor for displacing back and forth the at least one vario-magnet units along the corresponding bisecting direction.

7. The electron accelerator according to claim 3 , further comprising deflectors configured for:
orienting the electron beam which reaches the cavity outlet aperture from the first radial trajectory to a trajectory parallel to a bisector of the angle formed by the first and second radial trajectories at the central axis, Zc, prior to being deflected circularly by the magnetic unit, and
orienting the electron beam which reaches the cavity inlet aperture from a trajectory parallel to the bisector following the circular deflection imposed by the magnetic unit, to the second radial trajectory upon being re-introduced into the resonant cavity.

8. The electron accelerator according to claim 2 , wherein the second length is equal to the sum of the adding length, L+, and one or more halves of a wavelength, λ, of the electric field, E.

9. The electron accelerator according to claim 1 , further comprising;
a single vario-magnet unit, which is positioned directly upstream of the outlet, wherein
wi is the energy gained or lost by an electron beam upon one pass across the resonant cavity to a magnet unit or from a magnet unit, with
the value of wi being constant for i=1 to N, and with
the value of the energy gain, wi, for the last pass of the electron beam across the resonant cavity to the outlet being comprised between (−wi) and (+wi),

and wherein N is equal to 6, wi is equal to 1 MeV/pass for i=1 to 6 and comprised between −1 and 1 MeV/pass for a last pass, and wherein the extracted electron beam is comprised between 5 and 7 MeV.

10. The electron accelerator according to claim 1 , wherein each of the N magnet units forms a magnetic field in the deflecting chamber comprised between 0.01 T and 1.3 T.

11. The electron accelerator according to claim 1 , wherein the electron beam has an average power comprised between 30 and 700 kW.

12. The electron accelerator according to claim 1 , wherein the resonant cavity is formed by:
a first half shell, having a cylindrical outer wall of inner radius, R, and of central axis, Zc,
a second half shell, having a cylindrical outer wall of inner radius, R, and of central axis, Zc, and
a central ring element of inner radius, R, sandwiched at the level of the mid-plane, Pm, between the first and second half shells,
wherein a surface forming an outer conductor section is formed by an inner surface of the cylindrical outer wall of the first and second half shells, and by an inner edge of the central ring element, which is flush with the inner surfaces of both first and second half shells.

13. The electron accelerator according to claim 3 , wherein the first and second set of magnets are configured for generating a magnetic field to a first and second deflecting chambers respectively, the first deflecting chamber being in fluid communication with the second deflecting chamber by one or more windows.

Assignees

• Ion Beam Appl Sa

Inventors

• Abs Michel
• Brison Jeremy
• Kleeven Willem

Classifications

• H05H13/10 Primary

  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} · CPC title

• H05H7/18 Primary

  Cavities; Resonators {(travelling-wave tubes H01J23/18; hyperfrequency cavities in general H01P7/04, H01P7/06)} · CPC title

• H05H7/04

  Magnet systems {, e.g. undulators, wigglers (free-electron laser H01S3/0903)}; Energisation thereof · CPC title

• H05H2007/046

  for beam deflection · CPC title

• H05H2007/045

  for beam bending · CPC title