DK2339899T3 - Compact source of generation of charged particles - Google Patents

Description

-1-

The object of the present invention relates to a device and a method that allows a compact electron source to be provided.

It can also be used to produce particles carrying a charge, such as ions, for example, H+ ions.

Linear particle accelerators can use an accelerating electromagnetic field of the radiofrequency type. These accelerators operate with all types of charged particles but share the requirement for feeding the accelerator with ultra-high radiofrequency powers that generally originate from an electron tube, such as a klystron or a magnetron. This power tube operates in a pulsed manner and is fed by rectangular pulses having voltages capable of reaching several tens of kV. Indeed, the flat of the pulse is needed in order to avoid a drift in the power of the tube or even a change in the mode.

Various devices are required between the tube modulator and the linear accelerator in order for correct matching to be carried out: • the radiofrequency tube itself, which converts the voltage pulse into radio frequency power; • the synchronisation of the tube and accelerator pulses; • the tube output window, which allows the transition between the internal vacuum of the tube and the output that is generally in air or SF6 gas; • the radiofrequency or RF guides that carry the power to the linear accelerator.

Patent US 4027193 discloses a klystron and an accelerating structure disposed in the same chamber.

Patent US 4956219 discloses a pumping device comprising a first pump for the primary vacuum and a second pump for the secondary vacuum.

Patent US 6809325 relates to a device for generating and selecting heavy ions for the treatment of cancer.

The idea for the present invention is particularly based on the integration of a radiofrequency source and a particle accelerator section in a common and evacuated chamber, with a common pulsed feed between the radiofrequency section and the accelerator section for feeding the accelerator with the required high voltage RF power.

The invention relates to a compact device for generating particles carrying a charge, such as electrons, comprising at least the following elements disposed in a single chamber evacuated using a vacuum system: a first charged particles accelerator section comprising a first means for generating accelerated particles in an accelerator section, said particles accelerator section being fed with high voltage HF power using the power generated by a second section that is made up of at least one second means for generating packets of particles, which means generate HF power that is different to that which is produced by modulating the speed of the particles, where the accelerator section of the device comprises an accelerating structure comprising a set of cavities disposed in series relative to each other, said accelerating structure receiving RF power from the tube section that is produced by the electrons detached from the second cathode passing through a first cavity, which produces a first speed modulation, generating packets of electrons that will interact with a second cavity or extraction cavity acting as a resonator producing the -2- HF power that will feed the cavities disposed in series via an adapted physical link, and characterised in that said chamber comprises at least the following elements: • a cathode support receiving a first cathode used for the accelerator section and a second cathode belonging to the power generator tube. A cathode can be a thermo-ionic cathode fed by a thermal filament or even a nanotube-based cathode.

The vacuum system is, for example, made up of a first pump for the primary vacuum and a second pump for the secondary vacuum, with the vacuum that is produced being common to the two sections thai are disposed in the chamber.

The device according to the invention is, for example, used in a system comprising a guide that is disposed at the output of the structure of the cavities that allows the beam that is produced to be directed to a product or a section to be treated and it comprises a module for deflecting the beam of the particles, as well as a collector for said particles.

The device can also be used to generate H+ ions, protons (sic).

Further features and advantages of the device according to the invention will become apparenl upon reading the following description of an embodiment, which is provided by way of a non-limiting example, with reference to the single figure 1, which represents an example of the architecture of the compact device according to the invention.

Figure 1 describes an example of a compact source of electrons according to the invention.

The device according to the invention comprises a chamber 1 that is linked to a vacuum system that, for example, is made up of a first pump 2j for the primary vacuum and a second pump 22 for the secondary vacuum. The evacuated chamber 1 is connected to ground or to earth by a suitable device 3. A modulator 4 feeds the device with high voltage. An isolating section 5 creates the division between the high voltage modulator 4 and the connection to ground of the chamber. The chamber further comprises a temperature controlled cooling device that is not shown for the sake of simplification. A cathode support 6 will receive a first cathode 7 used for the accelerator section and a second cathode 8 belonging to the tube.

With respect to the accelerator section of the device, an accelerating structure 9 is, for example, made up of a set of cavities 9i disposed in series relative to each other. Further devices, such as a drifl spaces, focusing magnets, may also be needed in order to correctly condition the electrons so that they can be accelerated in an optimal manner. This structure will receive RF power in order to allow the acceleration of the electrons detached from the second cathode 8. The electrons propagate along an axis Ai. A guide 10 at the output of the accelerating structure allows the beam of the electrons thus created to be directed towards a target or an object 11. The beam of electrons, after it interacts with this object 11, is, for example, deflected by a suitable means 12 and is collected by a collector 13, the structure of which is known to a person skilled in the art.

The high voltage RF that is fed to the structure, as described hereafter, will accelerate the electrons in the cavities. -3- A module 14 that is fed with high voltage is disposed between the cathode 7 and the input E9 of the cavity in order to improve the quality of the beam. The particular function of this module is to prevent the beam of electrons produced by the cathode 7 from splitting, it pre-accelerates the electrons before they penetrate the accelerating cavities. The beam of electrons experiences strong acceleration gradients on the gun in order to bring it to relativistic energy levels where the effects of space charges are attenuated.

The section of the tube comprises a cathode 8 that feeds the electrons that, in this embodiment, will pass through a first cavity 20, which produces a first speed modulation, with the speed dispersion of the electrons being transformed after the drift space by an increase in the intensity of the beam as a result oi placing the electrons in packets. These packets of electrons propagate along an axis A2 and will interad with one or more extraction cavities 21, the one or more positions of which are optimised for a maximum extraction of power, with the cavity acting as a resonator that is excited by the successive packets oi electrons q. The cavity 21 will therefore oscillate at the rate of the passage of the packets of electrons. The resonating cavity generates the HF power that gradually increases, by sampling the energy from the packets of electrons. This HF power is in-phase with the oscillation generated at the beginning. Part of this HF power will feed the cavities disposed in series via an adapted physical link 23. The power of the beam of electrons that is not used during the interaction can be collected by a collection device 24. Such a device can, where necessary, use the depressed collector technique, i.e. a collector produced as a plurality of sections raised to different voltages in order to improve the yield of the assembly.

Further variants of embodiments of the device can be realised without departing from the scope oi the invention.

One example for implementation can be the use of a structure of the klystron type for the integrated radiofrequency tube. The klystron principle involves converting a speed modulation of the beam of electrons obtained via a modulation cavity into a modulation with an intensity that allows the extraction cavity to resonate through a drift space, which in certain cases can be long for the ultra-high voltages as the rapid electrons take longer to catch the slower electrons, with the difference in speed becoming low for high energy electrons.

The production of HF power can be obtained by means other than modulating the speed of the electrons as proposed for the nominal operation of the device.

It is thus possible for a direct modulation of time intensity to be produced for the source section and for the accelerator section by using a direct modulation principle that is known to a person skilled in the art and is disclosed, for example, in patent US 5506473.

Therefore, instead of using a speed modulation of the electrons produced by the presence of the cavities 21,22, the modulation of the intensity of the electrons can also be used.

The cavities can be replaced by a beat f, 3f in order to directly obtain the packets of electrons for the source RF, a post-acceleration continues by applying a sufficient DC direct field for the grouped packets before the extraction.

The first and second cathodes 7, 8 can be made up of a thermo-ionic cathode activated by a thermal filament. -4-

The cathodes 7, 8 also can be nanotube-based cathodes that have the particular advantage of being highly compact and of providing significant current densities.

The various elements that make up the invention are connected via means that are suitable for the vacuum technologies used. Therefore, the installation of the elements can require the use of adapted clamps and valves that allow the sections to be disconnected in order to simplify maintenance, for example.

The high voltage transition that is capable of providing the air/vacuum transition and of maintaining good pulsed isolation at several hundred kV also becomes common to the radiofrequency tube and the accelerator.

The previously described invention generally can be applied to the generation of charged particles or particles carrying a charge.

For example, the protons are generated from a plasma-based device, such as a magnetron.

The H+ ions can be generated with a magnetron that is made up of a cylindrical central cathode wrapped by an anode. The discharge voltage is generally higher than 150V and the drain current is approximately 40 A. A magnetic field of approximately 0.2 tesla is parallel to the axis of the cathode. The hydrogen gas that is used is introduced via a pulsed valve.

The device according to the invention provides a compact particle accelerator, in which the pulsed feed is common to the radiofrequency tube section integrated in the linear accelerator to feed the RF power and the accelerator gun, as they both require voltages of several hundred kV in order to operate at the bes1 levels of performance.

The device according to the invention has the particular advantage of not using an output window that is commonly used when the tube and the accelerating section are separate. In the present invention, the vacuum is common to the integrated radiofrequency tube and the particle accelerator. This is also the case for the cooling circuits and, where necessary, for the focusing structures, which also can be common. Using accelerator evacuation technologies (the use of clamps to connect the various sections of the system together instead of the sealed technology of conventional tubes) improves the ease of upgrades and improves maintainability.

Simplifying the architecture will reduce costs and will improve the compactness of the assembly.

As the structures of RF cavities are naturally matched to the same frequency, assuming there are structures of the same type for the two functions (tube and accelerator) and the same cooling circuit, the temperature and thus the frequency drifts are substantially identical. This allows the correct operation of the assembly to be maintained without requiring excessively precise temperature control.

Claims (5)

-5- COMPACT SOURCE FOR GENERATION OF CHARGED PARTICLES A compact device for generating a charge-carrying particle, such as electrons, comprising the following elements located in a single chamber (1) evacuated using a vacuum system (2): a first accelerator portion of charged particles comprising a first means (7) for generating the accelerated particles in an accelerator part (9), which particle accelerator part (23) is provided with HF high voltage power by means of the power generated by another part consisting of at least one other means ( 8,20,21) for generating particle packages, the agent generating HF power different from that produced by modulating the velocity of the particles, the accelerator part of the device comprising an accelerating structure (9) comprising electric sets of cavities (9h 92, ...) arranged in a series relative to each other, which accelerating structure (9) receives is RF power from the tube portion produced by the electrons detached from the cathode ( 8) passing through first cavity (20) which produces a first velocity modulation, thereby generating electron packets which will interact with a second cavity or extraction cavity (21) acting as a resonator producing the HF effect which will supply the voids positioned in a row via a adapted physical connection (23), characterized by. the chamber (1) comprising at least the following elements: a cathode support (6) for receiving a first cathode (7) used for the accelerator portion and a second cathode (8) forming part of the power generator tube. Device according to claim 1, characterized in that a cathode (7, 8) is a thermoionic cathode provided with a thermal filament. Device according to claim 1, characterized in that a cathode (7, 8) is based on nanotubes. Device according to claim 1, characterized in that the vacuum system consists of a first pump (2t) for some primary vacuum and a second pump (22) for the second vacuum, wherein the vacuum generated is common to the tc units, that is located in the chamber. Use of the device of claim 1 for generating and accelerating H + ions, protons.