Source: http://www.google.com/patents/US8073107?dq=inventor:%22Arthur+R.+Hair%22
Timestamp: 2014-09-02 19:22:39
Document Index: 579548955

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Patent US8073107 - Betatron with a contraction and expansion coil - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA betatron, especially in X-ray testing apparatus is provided, that includes a rotationally symmetrical inner yoke having two interspaced parts, an outer yoke connecting the two inner yoke parts, at least one main field coil, a toroidal betatron tube arranged between the opposing front sides of the inner...http://www.google.com/patents/US8073107?utm_source=gb-gplus-sharePatent US8073107 - Betatron with a contraction and expansion coilAdvanced Patent SearchPublication numberUS8073107 B2Publication typeGrantApplication numberUS 12/431,634Publication dateDec 6, 2011Filing dateApr 28, 2009Priority dateOct 28, 2006Also published asCA2668049A1, CN101530001A, CN101530001B, DE102006050953A1, EP2082625A1, EP2082625B1, US20090268872, WO2008052614A1Publication number12431634, 431634, US 8073107 B2, US 8073107B2, US-B2-8073107, US8073107 B2, US8073107B2InventorsJoerg BERMUTH, Georg Geus, Gregor HESS, Urs VIEHBOECKOriginal AssigneeSmiths Heimann GmbhExport CitationBiBTeX, EndNote, RefManPatent Citations (17), Classifications (10), Legal Events (1) External Links: USPTO, USPTO Assignment, EspacenetBetatron with a contraction and expansion coilUS 8073107 B2Abstract A betatron, especially in X-ray testing apparatus is provided, that includes a rotationally symmetrical inner yoke having two interspaced parts, an outer yoke connecting the two inner yoke parts, at least one main field coil, a toroidal betatron tube arranged between the opposing front sides of the inner yoke parts, and at least one contraction and expansion coil. An individual CE coil is respectively arranged between the front side of the inner yoke part and the betatron tube, and the radius of the CE coil is essentially the same as the nominal orbital radius of the electrons in the betatron tube.
a torus-shaped betatron tube arranged between opposing front sides of the inner yoke parts; and
at least one contraction and expansion coil, whereby in each case precisely one contraction and expansion coil is arranged between a front side of an inner yoke part and the betatron tube, wherein the radius of the contraction and expansion coil is substantially the same as the nominal orbit radius of the electrons in the betatron tube, and wherein each contraction and expansion coil is configured to perform both contraction and expansion of the electron orbit radius.
2. The betatron according to claim 1, wherein the same contraction and expansion coil is configured to both focus the electrons on the nominal orbit during an injection phase and to deflect the electrons onto a target during a deflection phase.
3. The betatron according to claim 1, wherein the opposing front sides of the inner yoke parts are formed and arranged with mirror symmetry to one another.
4. The betatron according to claim 1, wherein at least one main field coil is arranged on the inner yoke or on a neck or a shoulder of the inner yoke.
5. The betatron according to claim 4, further comprising two main field coils, wherein a main field coil is arranged on each of the inner yoke parts.
6. The betatron according to claim 1, wherein at least one round plate is arranged between the inner yoke parts, and wherein the round plate is arranged so that its longitudinal axis substantially coincides with the rotational symmetry axis of the inner yoke.
7. The betatron according to claim 1, wherein the connections of at least one of the contraction and expansion coils are connected to a current or voltage source and wherein, in at least one line, a switch actuatable by control electronics is arranged between the contraction and expansion coil and the current or voltage source.
8. The betatron according to claim 7, wherein the control electronics are configured such that the turn-on time and the turn-on duration of the switch are variable.
9. The betatron according to claim 8, further comprising a detector to determine the radiation intensity generated by the betatron.
10. The betatron according to claim 9, wherein the detector is connected to the control electronics and the turn-on time and the turn-on duration of the switch is determined by the control electronics from an output signal of the detector.
11. An x-ray inspection system for security inspection of objects, comprising:
a betatron, the betatron comprising:
12. The betatron according to claim 7, wherein the switch is an IGBT (insulated gate bipolar transistor).
X-ray inspection systems such as the one illustrated in FIG. 5 are used, as is well-known, in the inspection of large-volume articles such as containers and motor vehicles for illegal contents such as weapons, explosives, or contraband goods. In so doing, x-radiation is produced and directed at the article (e.g., target 50). The x-radiation attenuated by the object is measured by means of a detector (e.g. x-ray detector 52) and analyzed by an evaluation unit (e.g., evaluation unit 54). Therefore, a conclusion can be reached on the nature of the object. This type of x-ray inspection system is known, for example, from European Pat. No. EP 0 412 190 B1, which corresponds to U.S. Pat. No. 5,065,418.
1 2 ⁢ ⅆ ⅆ t ⁢ 〈 B ⁡ ( r s ) 〉 = ⅆ ⅆ t ⁢ B ⁡ ( r s ) with ⁢ ⁢ 〈 B ⁡ ( r s ) 〉 = 1 π � r S 2 ⁢ ∫ ∫ A ⁢ B ⁡ ( r ) ⁢ ⅆ A . In this case, rs is the nominal orbit radius of the electron, A the area defined by the nominal orbit radius rs, and <B(rs)> the magnetic field strength averaged over the area A.
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a betatron that does not have the aforementioned disadvantages.
At the end of the acceleration process, the electrons are directed onto the target during the deflection phase. To this end, the contraction and expansion coil is again supplied with current. The current flow through the CE coil during the deflection of the electrons is also called an expansion pulse. At this time, the main field coils produce a stronger magnetic field than during the injection phase. The material of the yoke and the round plates is located in a nonlinear region of the hysteresis curve, which describes the association between the exciting magnetic flux and the magnetic flux in the material. The magnetic flux in the material is influenced differently than during the injection phase in relationship to the magnetic flux in the air between the inner yoke parts, therefore, by the contraction and expansion coil. This results in a disturbance of the Wideroe condition, which is now again fulfilled by a changed nominal orbit radius. The electrons move in a spiral path to the changed nominal orbit radius and during this movement impact the target.
FIG. 5 shows a conventional x-ray inspection system for security inspection of objects.
DETAILED DESCRIPTION FIG. 1 shows the schematic structure of a preferred betatron 1 in cross section. It includes, inter alia, a rotationally symmetric inner yoke of two spaced-apart parts 2 a, 2 b, four optional round plates 3 between inner yoke parts 2 a, 2 b, whereby the longitudinal axis of round plates 3 corresponds to the rotational symmetry axis of the inner yoke, an outer yoke 4 connecting the two inner yoke parts 2 a, 2 b, a torus-shaped betatron tube 5 arranged between inner yoke parts 2 a, 2 b, two main field coils 6 a and 6 b, and control electronics 8, which are not shown in FIG. 1. Main field coils 6 a and 6 b are arranged on shoulders of inner yoke parts 2 a or 2 b. The magnetic field produced by them penetrates the inner yoke parts 2 a and 2 b and the region between their opposite front sides, whereby the magnetic circuit is closed by outer yoke 4. The shape of the inner and/or outer yoke can be selected by the person skilled in the art depending on the application and can deviate from the shape shown in FIG. 1. Only one or more than two main field coils may also be present. A different number and/or shape of the round plates are likewise possible.
1 2 ⁢ ⅆ ⅆ t ⁢ 〈 B ⁡ ( r s ) 〉 = ⅆ ⅆ t ⁢ B ⁡ ( r s ) is the stable nominal orbit radius in which the electrons circulate.
The electron gun emits the electrons with a known opening angle, whereby the distribution of the electrons over this opening angle typically is not constant. In addition, the electron gun injects the electrons onto an injection radius r1 differing from the nominal orbit radius rs. It is therefore necessary first to transfer the electrons from the injection radius r1 to the nominal orbit radius rs. The two contraction and expansion coils 7 a and 7 b, which are arranged between the front sides of inner yoke parts 2 a or 2 b and betatron tube 5 are used to this end. The CE coils are indicated in FIG. 1 by three spiral windings, whereby, however, any other design is possible. The radius of CE coils 7 a and 7 b is substantially the same as the nominal orbit radius rs of the electrons in betatron tube 5. Owing to the spatial expansion of CE coils 7 a and 7 b, their outer edges extend slightly beyond the nominal orbit radius rs. The precise size and positioning of the CE coils is left to the person skilled in the art practicing the invention. The condition must be maintained, however, that the inner radius of CE coils 7 a and 7 b is greater than the outer radius of round plates 3, so that the magnetic field produced by them also penetrates parts of the region outside round plates 3.
The central axes of CE coils 7 a and 7 b coincide with the rotational symmetry axis of the inner yoke. Because of this arrangement and the size of CE coils 7 a and 7 b, the magnetic field produced by them penetrates a circular area whose radius is greater than the radius of round plates 3 and lies approximately within the range of the nominal orbit radius rs.
If a current, the so-called contraction pulse, is impressed in CE coils 7 a and 7 b, the course B′(r) of the magnetic field strength versus the radius, as drawn as a broken line in FIG. 2, results qualitatively as a superposition of the magnetic fields of main field coils 6 a, 6 b and CE coils 7 a, 7 b. In the case of this resulting magnetic field, the changed nominal orbit radius rs′fulfills the Wideroe condition. It follows that the electrons are drawn into a spiral path from the injection radius r1 to the changed nominal orbit radius rs′. In this case, the electrons, for example, depending on their injection angle into betatron tube 5, pass the desired nominal orbit radius rs at different time points. The electrons at the end of the contraction pulse or in the vicinity of the desired nominal orbit radius rs are then accelerated to this radius.
At the end of the acceleration process, main field coils 6 a and 6 b produce the magnetic field B(r), which is shown qualitatively in FIG. 3 as a solid line and whose course corresponds substantially to the magnetic field of FIG. 2. Because of the higher current through main field coils 6 a and 6 b, the magnetic field is much greater, however. In addition, the material of the yoke and/or the round plates is in a nonlinear region of the hysteresis curve. When CE coils 7 a and 7 b are supplied with the so-called expansion pulse, accordingly the superposed magnetic field B″ (r), shown as a broken line in FIG. 3, is obtained. Proceeding from this superposed magnetic field, the changed nominal orbit radius rs″ fulfills the Wideroe condition. It follows that the electrons drift on a spiral path from nominal orbit radius rs valid during the acceleration in the direction of the changed nominal orbit radius rs″. During this drifting motion, the electrons impact the target and thereby produce x-radiation.
FIG. 4 shows by way of example an electric circuit for supplying current to CE coil 7 a, which can be applied identically to CE coil 7 b. CE coil 7 a is connected via a switch 9 controllable by control electronics 8 to a voltage source 11. Optionally, several CE coils are connected via one or more switches to a common voltage source. Furthermore, alternatively, each CE coil is connected via a separate switch to a voltage source assigned to the CE coil.
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