Abstract
Beam current variation system for a cyclotron, arranged in the inner center of the cyclotron, downstream from the ion source generating the charged particle beam, the system comprising a deflector system powered by a voltage and a collimator. The beam is dumped in the collimator, if the deflector system (10; 20, 21) is not powered, and the beam is switched on by powering the deflector system with a voltage.
Claims
1. A beam current variation system for a cyclotron, arranged in the inner centre of the cyclotron, downstream from an ion source generating a charged particle beam, the system comprising a deflector system powered by a voltage for deflecting the beam and a collimator, characterized in that the beam is dumped in the collimator, when the deflector system is not powered, and in that the beam is switched on by powering the deflector system with a voltage.
2. The beam current variation system according to claim 1, characterized in that a beam current intensity may be continuously varied by variation of the voltage powering the deflector system.
3. The beam current variation system according to claim 1, characterized in that the deflector system comprises a deflector arranged upstream from the collimator, wherein the beam enters into the deflector along a central plane of the deflector.
4. The beam current variation system according to claim 1, characterized in that the deflector system comprises a deflector arranged upstream from the collimator, wherein the beam enters into the deflector slantwise.
5. The beam current variation system according to claim 3, characterized in that the deflector and the collimator are dis-aligned in such a way that the beam is dumped in the collimator, when no voltage is applied to the deflector.
6. The beam current variation system according to claim 1, characterized in that the deflector system comprises a first deflector, arranged upstream from the collimator, and a second deflector, arranged downstream from the collimator, wherein the beam is dumped in the collimator, when the first deflector is not powered, and wherein the beam passes through the collimator, when the first deflector is suitably powered, and wherein the second deflector changes the beam direction towards an original beam direction which the beam had before entering the first deflector.
7. The beam current variation system according to claim 6, characterized in that the beam is directed towards an acceleration plane of the cyclotron with the second deflector.
8. The beam current variation system according to claim 1, characterized in that, after switching the beam on by deflection in the deflection system, the beam ends up in an acceleration plane of the cyclotron.
9. The beam current variation system according to claim 1, characterized in that one or more deflectors of the deflector system deflect the beam perpendicular to an acceleration plane.
10. The beam current variation system according to claim 1, characterized in that one or more deflectors of the deflector system deflect the beam laterally in an acceleration plane.
11. The beam current variation system according to claim 2, characterized in that the deflector system comprises a deflector arranged upstream from the collimator, wherein the beam enters into the deflector along a central plane of the deflector.
12. The beam current variation system according to claim 2, characterized in that the deflector system comprises a deflector arranged upstream from the collimator, wherein the beam enters into the deflector slantwise.
13. The beam current variation system according to claim 4, characterized in that the deflector and the collimator are disaligned in such a way that the beam is dumped in the collimator, when no voltage is applied to the deflector.
14. The beam current variation system according to claim 2, characterized in that the deflector system comprises a first deflector, arranged upstream from the collimator, and a second deflector, arranged downstream from the collimator, wherein the beam is dumped in the collimator, when the first deflector is not powered, and wherein the beam passes through the collimator, when the first deflector is suitably powered, and wherein the second deflector changes the beam direction towards an original beam direction which the beam had before entering the first deflector.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Preferred embodiments of the invention will now be explained in detail below with reference to the figures, in which:
(2) FIG. 1: shows a view onto the acceleration plane with the first few turns of the spiral beam path
(3) FIG. 2: shows, in a view parallel to the acceleration plane, the beam path through a deflector and collimator according to the prior art,
(4) FIG. 3: shows the beam path through the deflector system and the collimator according to a first embodiment of the invention,
(5) FIG. 4: shows the beam path through the deflector system and the collimator according to a second embodiment of the invention, and
(6) FIG. 5: shows the beam path through the deflector system and the collimators according to a third embodiment of the invention.
DETAILED DESCRIPTION
(7) FIG. 1 shows a view onto the first few turns of the beam 1 in the acceleration plane. The beam starts at the ion source 2 and follows a spiral beam path in the magnetic field generated by the—in this case four—dees 3 of the cyclotron. As shown in FIG. 1, the beam 1 passes through the deflector 10 consisting of a pair of deflector plates generating an electric field perpendicular to the acceleration plane. On its further path after the deflector 10, the beam 1 proceeds to the collimator 15.
(8) FIG. 2 shows in a view parallel to the acceleration plane 4 an arrangement of deflector 10 and collimator 15 according to the prior art. The deflector 10 consists of a pair of parallel deflector plates. The central plane of the deflector coincides with the acceleration plane 4. The beam 1 enters from the left-hand side into the deflector 10 along the central plane of the deflector and perpendicular to the electric field generated by the deflector. If the deflector is powered with a voltage of +/−3.5 kV the beam 1 is deflected in such way that it is totally dumped in the collimator 15. If no voltage is applied to the deflector 10, the beam 1 passes straight through the collimator 15 along the dashed line and proceeds to the further acceleration in the acceleration plane 4.
(9) FIG. 3 shows a first embodiment of the invention, wherein the beam current variation system is formed by a deflector 10 and a collimator 15 arranged downstream from the deflector 10. The deflector 10 consists of a pair of parallel deflector plates and is powered by a voltage and deflects the beam by an electro-static field, if a voltage is applied. In FIG. 3, the charged particle beam, coming from the left, enters into the deflector 10 along the central plane 11 of the deflector 10, perpendicular to the electrostatic field generated by the deflector 10. If no voltage is applied to the deflector 10, the beam passes through the deflector on the dashed line, i.e. straight through along the central plane of the deflector 10. The collimator 15 is arranged in such way that the beam 1 is totally dumped in the collimator, if no voltage is applied to the deflector 10. This means that the deflector 10 and the collimator 15 are disaligned with respect to the beam 1 is such way that the beam is switched off, if the deflector is not powered. If a suitable voltage is applied to the deflector 10, the beam is deflected in such way that it traverses the deflector along the continuous beam line 1 and passes through the collimator 15 in order to proceed to the further acceleration in the acceleration plane 4 of the cyclotron. On this way, downstream from the collimator 15, the beam 1 may be focused and/or redirected in the region 30 in an electric and/or magnetic field.
(10) By varying the voltage around the value where the beam passes the opening in the collimator, the intensity of the beam current may be continuously varied.
(11) FIG. 4 shows a second embodiment of the invention, wherein the beam current variation system is also formed by a deflector 10 and a collimator 15 arranged downstream from the deflector 10. In this embodiment, as shown in FIG. 4, the beam 1, coming from the left, enters the deflector 10 slantwise, i.e. not parallel to the central plane 11 of the deflector, but with some inclination with respect to the electric field generated by the deflector 10. If no voltage is applied to the deflector 10, the beam passes through the deflector 10 on the dashed line, i.e. with some inclination with respect to the central plane 11 of the deflector 10. The collimator 15 is arranged in such way that the beam 1 is totally dumped in the collimator 15, if no voltage is applied to the deflector 10. This results in a beam switch off, if the deflector is not powered. If a suitable voltage is applied to the deflector 10, the beam 1 is deflected in such way that it traverses the deflector along the continuous beam line 1 and passes through the collimator 15 in order to further proceed to the further acceleration. On this way, downstream from the collimator 15, the beam 1 may be focused and/or redirected in the region 30 in an electric and/or magnetic field.
(12) FIG. 5 shows a third embodiment of the invention, wherein the beam current variation system is formed by a first deflector 20, a collimator 25 arranged downstream from the first deflector 20, and a second deflector 21 arranged downstream from the collimator 25. The deflectors 20, 21 consist of pairs of parallel deflector plates and are powered by a voltage and deflect the beam 1 by an electrostatic field, if a voltage is applied. As shown in FIG. 5, the beam, coming from the left, enters the first deflector 20 in a direction perpendicular to the electric field along the central plane of the first deflector 20. If no voltage is applied to the first deflector, the beam 1 traverses the deflector on the dashed line, i.e. straight along the central plane of the deflector. The collimator 25 is aligned in such way that the beam 1 is totally dumped in the collimator, if no voltage is applied to the first deflector 20. This way the collimator is actually a beam dump. If a suitable voltage is applied to the first deflector 20, the beam 1 is deflected in such way that the beam 1 traverses the first deflector 20 along the continuous beam line. The beam is deflected in such way that it passes around the collimator 25 and enters into the second deflector 21. In the second deflector 21 the beam 1 is deflected in a direction back towards its original direction in order to proceed to the further acceleration in the acceleration plane 4. On this way, in the region 30 downstream from the second deflector 21, the beam may be focused and/or redirected in an electric and/or magnetic field.
(13) The three preferred embodiments described above provide that the beam 1 is completely switched off if no voltage is applied to the deflector system 10 or 20, 21. Thus the invention provides the advantage of beam current variation system which is fail-safe with respect to switch off.
