Radiant energy – With charged particle beam deflection or focussing – Magnetic lens
Reexamination Certificate
2002-01-18
2003-09-09
Lee, John R. (Department: 2881)
Radiant energy
With charged particle beam deflection or focussing
Magnetic lens
C250S398000
Reexamination Certificate
active
06617586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a beam delivery system and in particular to a beam delivery system that controls an electron beam by means of electromagnets having a common magnetic return yoke.
2. Description of Related Art
Electro-magnets are used to control electron beams in the process of irradiating surfaces of products. Conventional techniques use scanning magnets for this purpose. One of the drawbacks of using scanning magnets is the fact that they are very large. They have to be large since a considerable distance between the magnets and the products being radiated is required to obtain an even distribution of the beam over the whole surface. Moreover, since the conventional arrangements are very large, a large amount of shielding is required to contain the radiation.
Various different types of systems use scanning magnets as the electron beam directing means. Two such systems are shown in the appended drawings.
FIG. 1
schematically shows a conventional single sided scanning system and
FIG. 2
schematically shows a conventional two sided scanning system. Both of these systems, as can be seen, are constructed to direct an accelerated beam of electrons evenly onto a product. Since the irradiation of products in industrial applications is, in general, performed on consecutive products that are moving along in some direction with respect to the system, it is of the utmost importance to ensure that each of the passing products gets an equal amount of radiation, and furthermore that the whole surface of the products gets irradiated.
In the illustrated types of conventional system, the electron beam is composed of short pulses (microseconds) of electrons, with a longer (milliseconds) time gap between them. As a result, the cross-sectional area of the beam must be enlarged from the concentrated form in which it was generated before it impinges on the surface, to avoid “spots” or “stripes” of radiation on the irradiated products. In addition, the system that controls the delivery of the beams onto the products to be radiated must be capable of directing the pulses onto every possible area of the total surface of each product.
This results in the problem that it is difficult to optimize the size of the scanning magnets and the magnet-to-product distance while still achieving complete and uniform coverage of the total surface of the products, particularly since the optimum size necessary to prevent spots or stripes and ensure complete radiation coverage depends not only on scanning magnet size and distance, but also on the shape and orientations of the products to be irradiated, as can be understood from the example of a rectangular product that moves in a perpendicular direction with respect to the beams. In that case, some energy carried by the beam will inevitably be lost since the beam impinges on the surface in the form of a cone, and thus parts of the beam will radiate into the space at each side of the product. Furthermore, the sides of the product will not be adequately covered. To solve this problem, it is necessary to achieve better control of the beam delivery system, and particularly the ability to irradiate the boundaries of the product at beam angles that differ from perpendicular.
U.S. Pat. No. 4,295,048, Cleland et al., discloses an example of a method and a system for scanning a beam of charged particles in order to control a radiation dose distribution. The system is implemented by deflecting the beam through a plurality of positions along the conveyor path along which products that are to be irradiated are moving, through a single beam scanning device or a series of deflecting magnets arranged along a beam pipe. One drawback of this approach is the size of the system, which is significantly larger than the delivery system of the present invention. Furthermore, it is not possible, in a device of the type disclosed in U.S. Pat. No. 4,295,048, to direct beams in several directions without adjusting the beam delivery system mechanically, making it relatively difficult to control the beam.
SUMMARY OF THE INVENTION
It is therefore a first objective of the present invention to provide a beam delivery system that can be closer to the product and is easier to control, and that is capable of irradiating the boundaries of the product at beam angles that differ from the perpendicular.
It is a second objective of the present invention to provide a beam delivery system that has a distance to the products that is much smaller than in the prior art, and furthermore to provide a better controlled beam that can irradiate the products at controlled angles.
It is a third objective of the present invention to provide a beam delivery system that is much smaller than prior art systems.
It is a fourth objective of the invention to provide a system with optimized focusing of the beam.
It is a fifth objective of the invention to provide a beam delivery system that gives improved surface dose homogeneity on the product.
These objectives are achieved by a beam delivery system that includes a set of electronically controlled magnets with a common magnetic yoke. The invention uses a set of small magnets to steer the beam directly onto the products being irradiated with a very short distance between the magnets and the products. The system is used to control the distribution of charged particles over one or several product positions, and makes it possible to direct the beams onto desired positions on the product/products. Because of the short distance between the magnets and the products, it is possible to make the overall system much smaller and, as a consequence, much less shielding is demanded.
As this invention relates to a beam delivery system, those skilled in the art will recognize that, in all embodiments of the invention, a device that radiates charged particles, e.g. electrons, must be provided. This device might be an accelerator of electrons or any other suitable means that can provide a beam of charged particles. The beam of electrons may, for example, be used to irradiate a product that is passing an area where the surface of the product is being covered by charged particles. The surface of the product is preferably parallel to the initial, undirected beam, and moves in a direction that is close to and approximately perpendicular to the initial, undirected beam.
The beam delivery system of the invention includes both an accelerating means for accelerating charged particles and a beam directing means made up of sets of magnets, each magnet being constructed from a coil wound around a core leg and a magnetic pole face. All of the magnets have a common return yoke, the magnets being spaced along the axis of the yoke and perpendicular to the initial beam path, with a gap formed between opposite magnet pole faces and arranged such that pulses of an undisturbed beam emanating from the beam radiating device propagate in the gap. In the preferred embodiment, the beam or beam pulses propagate through a vacuum tube or a vacuum chamber. The magnetic fields, generated between opposite magnetic pole faces, are provided through the coils on “the leg parts” of the magnets, and these coils are connected by switches to one or a number of external power supplies.
The beam can be viewed as a train of electron pulses, where every pulse consists of a large amount of electrons, and the pulses are sent with time gaps between them. The first pulse is directed onto a predetermined position on the product by the first set of magnets, the second by subsequent sets of magnets and so forth. Control of the magnets may, in the preferred embodiment, be obtained through “synchronizing means” that synchronize the application of power to individual magnets or sets of magnets, with the timing of electron pulses supplied by the accelerator device, e.g., through the application of clock or timing pulses or signals. In addition, control of the magnets may be achieved by one or more computer controlled power supplies that supply differing amounts of power
Crewson Walter
Woodburn David
Bacon & Thomas PLLC
Kalivoda Christopher M.
Lee John R.
ScandiNova AB
LandOfFree
Beam delivery system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Beam delivery system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Beam delivery system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3078625