EP2198432B1 - Chopper for a particle beam - Google Patents

Abstract

A chopper for a particle beam comprises an annular guiding element and an element for controlling the intensity of the particle beam. The control element is supported on the guiding element so that at least one point under consideration on the control element can revolve along the circumference of the guiding element. Mounting along a circumference allows for accommodation of considerably higher disturbance torque than mounting on a rotational axle, using the same bearing force. Furthermore, it is possible to dispense with the entire rotational axle, and the control element can be designed, for example, as a ring. This brings about considerable weight savings as compared to chopper wheels according to the prior art, which accordingly enables higher circumferential speeds and therefore higher modulation frequencies for the particle beam, while at the same time increasing operational safety.

Description

State of the art

To divide a continuous particle beam into spatially and temporally limited pulses, choppers are used. A chopper is an element that has both particle-beam transmissive and particle-beam impermeable regions. When the chopper is moved through the particle beam, mutually permeable and impermeable regions pass through the particle beam so that the particle beam is modulated.

From the DE 10 2004 002 326 A1 are known as wheels formed chopper, which are rotated by the particle beam. An essential criterion for the performance of such a chopper is the highest frequency with which it can modulate the particle beam. This frequency is determined by the peripheral speed at the edge of the chopper wheel, which in turn is determined by the diameter and the speed.

The above document discloses that for typical experiments, peripheral speeds of about 300 m / s are required. The document discloses both designed as solid disks and spoke-shaped segmented chopper to achieve such rotational speeds.

The disadvantage of the material of the Chopperräder due to the centrifugal forces is claimed to the limits of its mechanical strength. In addition, the Chopperräder can get into vibration. In practice, speed ranges in which natural frequencies of the chopper wheels can be excited must be avoided. So it may happen that the chopper can not be operated at the rotational speed at which he would be able to from its mechanical strength.

Task and solution

It is therefore the object of the invention to provide a chopper which is able to modulate a particle beam with a higher frequency than hitherto possible and at the same time is safer to operate than chopper according to the prior art.

This object is achieved by a chopper according to the main claim. Further advantageous embodiments will be apparent from the dependent claims.

Subject of the invention

In the context of the invention, a chopper for a particle beam has been developed. This chopper is characterized by at least one annular, in particular annular, guide element and by at least one control element for the particle beam, which is mounted against the guide element such that at least one point on the control element is able to circulate along a circumference of the guide element.

A guide element in the sense of this invention is understood to be an element which imposes one or more constraints on the movement of the control element. The guide element should therefore at least be designed and / or fixed in space such that a movement of the control element during operation of the chopper does not trigger any movement of the guide element.

For the purposes of this invention, a control element is understood to be any element which has at least one region which is able to attenuate the intensity of the particle beam. In particular, this region can be completely impermeable to the particle beam. If the control is moved by the particle beam, the intensity of the particle beam can be modulated.

It was recognized that the inventive measures for the first time an alternative to the hitherto always designed as wheels choppers is provided. This will cause unwanted vibrations as a result the wheel-shaped training so far inevitably occurred, advantageously avoided. As a result, a chopper is provided which is able to modulate the particle beam at a substantially higher frequency than was possible in the prior art. However, the storage according to the invention along a circumference is functional and advantageous even at circulating frequencies of the point on the control along the circumference of the guide element, which are smaller than the maximum possible rotational frequency.

It has also been recognized that the storage according to the invention along a circumference, in particular with large circumferences and rotational speeds, is considerably more stable than the storage necessarily required on a rotation axis in the case of wheel-shaped choppers according to the prior art. In order to compensate for a given disturbance torque, according to the definition of the torque when stored along a circumference, a much smaller force is required than when mounted on a rotation axis. At the same time, the bearing force to be applied to be distributed over the entire circumference of the guide element, so that also higher overall bearing forces can be exerted on the control. As a result, the guide element can have a higher circumference and at the same time the control can be moved faster. Thus, the control can move at a higher peripheral speed. This causes the particle beam to be modulated at a higher frequency than was possible in the prior art.

The invention expressly includes a chopper wheel as a control element, wherein this may be formed as a solid disc or spoke-shaped segmented and wherein also a bearing can be present on a rotation axis. Thus, an existing chopper can be retrofitted with the storage according to the invention along a circumference. The benefits according to the invention then likewise come into play, in that for compensation of a given disturbance moment the bearing must apply less force along the circumference than the bearing on an axis of rotation and that altogether higher bearing forces can be exerted on the control element.

Since the control is mounted according to the invention close to the place of its function, the lever with which disturbance torques can attack the bearing, advantageously shortened. Thus, a given disturbance torque acts with a lower force on the bearing than when stored on a rotation axis according to the prior art. Thus, the danger is reduced that the bearing will be destroyed and the control or parts thereof fly away uncontrolled, for example, when the movement of the control is stopped abruptly by a foreign body.

In addition, a rotary axis is unnecessary altogether. There is also no need to mechanically connect parts of the control with a rotation axis. As a result, various shapes for the control are possible. It may, for example, annular, in particular annular, be formed. In particular, the control can be arranged concentrically to the guide element. However, the effect on the particle beam can be achieved even with a single control element, which is just large enough to attenuate the particle beam at a point of rotation around the circumference of the guide element. From a plurality of such individual control elements, a control can be composed, which is able to circulate as a whole around the circumference of the guide member. This control can, for example, occupy all or part of the circumference of the guide element. In the case of defects, such as radiation damage due to the interaction with the particle beam, the individual control elements can then be replaced independently of one another. The connection of the individual control elements can be elastic or solid.

Such shapes of the control can have a considerably lower weight than prior art chopper wheels. This weight also only grows linearly with the size of the control. Since the decisive for the maximum achievable modulation frequency peripheral speed is the product of speed and scope, the largest possible extent of the control is advantageous. By contrast, in a prior art (solid) chopper wheel, the weight is proportional to the area and thus grows quadratically with the circumference. The invention significantly lower weight in turn causes per unit bearing force, which on the control can be exercised, a higher peripheral speed and thus a higher modulation frequency can be achieved.

The lower weight improves the reliability of the chopper in two ways: it leads to a lower stress of the control by the centrifugal forces, so that the risk is reduced that this tears. In the unlikely event of tearing, the fragments also have a much lower mass and thus kinetic energy, so that a much lower effort for an enclosure must be driven, which protects the environment from such fragments.

At the same time, the lower weight also increases the natural frequencies of the control element so that they are advantageously no longer in the range of the circulating frequencies around the circumference of the guide element.

In an operation of the chopper in a vacuum, an annular shape of the control affects yet another advantageous manner. Only the guide element and the control must be in vacuum, but not the entire area bounded by these elements. It is thus sufficient if a tubular region which encloses the control and the guide element is kept under vacuum. In particular, this region can be arranged between an inner diameter that is smaller than the inner diameter of the control element and an outer diameter that is greater than the outer diameter of the guide element. This dramatically reduces the volume to be vacuumed. The cost of pump power and time for the production of this vacuum is reduced considerably.

The ring shape of the guide element according to the invention is not fixed to the circular ring shape. Other annular designs, such as ellipses, may be advantageous, for example, if the chopper is to be adapted to tight spatial conditions of an already existing experimental setup.

In a particularly advantageous embodiment of the invention, the control element has at least one region which is reflective for the particle beam. For this purpose, for example, a graphite monocrystal is suitable for a neutron beam. Then the portion of the particle beam not transmitted by the chopper can be used for another experiment. But he can also be led by another chopper. If both branches of the particle beam are combined, the result is modulated at a higher frequency than a single chopper could

In a further advantageous embodiment of the invention, the control element has at least one helical bore. At a given velocity of revolution, only particles within a narrow velocity window can then pass the control. The chopper then not only modulates the intensity of the particle beam, but also simultaneously selects the particles of the beam according to their velocity and thus their energy and momentum. Thus, chopper and speed selector are advantageously combined in one device. Since only one drive is required, such a combination device is more reliable than two individual devices. At the same time installation space is saved, which is particularly advantageous in space-constrained experimental arrangements and when operating in a vacuum.

The longer the helical bore, the narrower the velocity range of the particles that can pass. However, a longer bore increases the thickness and thus the weight of the control. Since the control according to the invention saves a great deal of weight elsewhere, it is possible, without compromising the stability, to make the area of the helical bore thicker.

It is conceivable that the control element is mounted against the guide element in such a way that the receptor point can circulate along the outer circumference of the guide element. In a particularly advantageous embodiment of the invention, however, the control element is mounted against the guide element such that the point of view is capable of circulating along the inner circumference of the guide element. In this embodiment, the control is pressed in operation by the centrifugal forces against the guide element. This increases the stability of the storage and at the same time also the operational safety: Even if the control should break, the guide element prevents the fragments from the radial fly away. A separate, elaborate enclosure of the chopper to protect the environment from debris is not required. The guide element already increases the reliability.

The storage of the control element against the guide element is in a particularly advantageous embodiment of the invention, a magnetic storage and in particular a permanent magnetic storage. Such storage is non-contact and thus wear-free even at high speeds. There is no lubricant required so that the bearing is fully ultra high vacuum compatible.

Advantageously, the guide element and the control element each have at least one magnetized region in such a way that these magnetized regions repel each other at the point of circulation of the point in which they come closest. If, for example, the control element has an annular shape and the magnetized areas are arranged point-symmetrically about the center of the ring, a rest position is defined in which all repulsions between magnetized areas are compensated. In a deflection from the rest position, a magnetic gap is reduced, so that the repulsive force between the corresponding magnetized areas increases and drives the control back to the rest position.

In a further advantageous embodiment, the bearing of the control on constraints in such a way that the control can neither move axially out of the guide element or tilt in this. This can be effected, for example, by additional magnetized areas on the control element and on the guide element, which, when in operation directly opposite one another, exert magnetic forces with an axial component on one another.

In a particularly advantageous embodiment of the invention, the guide element has means for generating a magnetic traveling field. Then can in addition to the magnetic bearing and the drive of the control via the guide element take place. This functional integration of drive and bearing is also able to respond to imbalances in the control by adjusting the strength of the traveling magnetic field over time. Such imbalances are very difficult to avoid in choppers with typical diameters of 1.20 m and more and peripheral speeds up to 300 m / s.

In an advantageous embodiment of the invention, at least one temporarily or permanently magnetized region of the guide element, which belongs to the magnetic bearing of the control element against the guide element, at the same time also an element for generating the magnetic traveling field. If the magnetized region is, for example, a coil which is energized for magnetic storage of the control element according to a time program, an additional current can be modulated onto this current, which generates the traveling magnetic field.

To achieve a maximum propulsion and thus a maximum rotational speed, the magnetic traveling field is advantageously perpendicular to the magnetic field of the magnetic bearing.

The technical teaching underlying the above statements is not limited to the application case chopper described in detail. Instead, it is generally taught that it is advantageous to design a, preferably magnetic, mounting of two, in particular mutually rotatable, components such that at least one Aufpunkt on the first component along a circumference of the second component is able to circulate, this second component advantageously designed annular is. The above-described advantages of such an arrangement according to the invention also come into play, for example, in the magnetic bearing of turbomolecular pumps or exhaust gas turbochargers.

In general, the approach offers a possibility, so far in the prior art by rotating around a rotation axis elements which achieve a physical effect in the region of its outer periphery, to modify such that the element is stored along the outer periphery. In this way, the axis of rotation and connections of any kind between this axis of rotation and the outer circumference can be partially or completely saved. As a result, the mass of the arrangement can be advantageously reduced, and the lever with which disturbance moments act on the bearing is advantageously reduced. The outer circumference can be tailored to the needs. It may for example be a closed loop, which may be arbitrarily oriented in space, for example in a vertical plane. The bearing carries the physical effect-achieving element, such as one or more turbine blades, beam stopper, filters, reflectors or energy selectors.

In particular, the turbomolecular pump and the exhaust gas turbocharger are characterized by particularly large disturbance torques which engage in a magnetic bearing on a shaft according to the prior art with a large lever on the camp. When storage according to the invention along a circumference of these disturbing moments attack only with a very short lever and thus can be better compensated by the camp. In general, the bearing force is distributed over the entire circumference of the second component, so that according to the invention overall significantly greater bearing forces can be absorbed than in the prior art. Also, the volume of construction of both turbomolecular pumps and exhaust gas turbochargers can be advantageously reduced by the inventive integration of drive and storage.

Special description part

Figur 1:

Ausführungsbeispiel des erfindungsgemäßen Choppers, entlang dessen Symmetrieachse betrachtet.

Figur 2:

Seitenansicht des Choppers aus Figur 1.

Figur 3:

Ausschnitt des Choppers aus Figur 1 in Schnittzeichnung.

Figur 4:

Dreidimensionale Ansicht des Choppers aus Figur 1.

The subject matter of the invention will be explained in more detail below with reference to figures, without the subject matter of the invention being restricted thereby. It is shown:

FIG. 1:

Embodiment of the chopper according to the invention, viewed along the axis of symmetry.

FIG. 2:

Side view of the chopper FIG. 1 ,

FIG. 3:

Detail of the chopper FIG. 1 in section drawing.

FIG. 4:

Three-dimensional view of the chopper FIG. 1 ,

Like reference numerals designate like elements.

FIG. 1 shows an embodiment of a chopper invention in a view along its axis of symmetry (the axis of symmetry is perpendicular to the plane). This chopper comprises an annular guide element 11 on a base 12 as well as a likewise annular, concentric with the guide element 11 arranged control element 13. The guide member 11 comprises a main body 11a and magnetic coils 11b. The main body 11a consists of a circular ring 11a1, which is arranged between two annular discs 11a2 and 11a3. The magnetic coils 11b are recessed at regular intervals in the inner side of the circular ring 11a1 of the main body 11a.

The control element 13 comprises a base ring 13a, permanent-magnetic regions 13b and areas 13c which are reflective for the particle beam and thus impermeable. The permanent magnetic regions 13b are sunk at regular intervals in the outer side of the base ring 13a. The particle-beam-reflecting and hence impermeable regions 13c are mounted at regular intervals on the inside of the base ring 13a.

The magnetic coils 11b and the permanent magnetic regions 13b cooperate in such a way that the control element 13 is mounted magnetically against the guide element 11. At the same time, the magnetic coils 11 b are also elements for generating a traveling magnetic field with which the control element 13 and thus also the areas 13 c reflecting the particle beam can be set into rotation within the guide element 11.

The main body 11 a surrounds the base ring 13 a almost completely except for a radially inwardly directed region in which the particle-beam-reflecting regions 13 c can protrude radially inward around the guide element 11 in each circulating position of the control element 13. Thus, the magnetic bearing of the control member 13 is supplemented against the guide member 11 by a mechanical emergency storage, which imposes such constraints on the control 13 that it can neither move axially out of the guide member 11 nor tilt in this

The embedding of the magnetic coils 11b in the main body 11a and the embedding of the magnetized portions 13b in the base ring 13a are only in the upper right quadrant of FIG. 1 to see, in which the chopper is partially shown in cross-section.

FIG. 2 shows a side view of the chopper FIG. 1 , Across from FIG. 1 the chopper is turned 90 degrees out of the drawing plane. Here, the subdivision of the main body 11a into a circular ring 11a1 and two annular disks 11a2 and 11a3 is illustrated.

In FIG. 3 a section of the chopper is shown in cross-sectional view, wherein the section along the line AA in FIG. 1 was carried out. The annular discs 11a2 and 11a3 of the main body 11a have at their directed to the common axis of symmetry of the guide member 11 and control element 13 edge extensions 11a4 and 11a5, which are directed towards each other. The projections 11a4 and 11a5 form a gap 11a6 into which the particle beam-reflecting region 13c of the control element engages and in which this region 13c can rotate.

In the direction of the base ring 13a of the control 13 facing edges of the annular discs 11a2 and 11a3 of the guide member 11 additional magnetized portions 11a7 and 11a8 are sunk. In the edges of the base ring 13a of the control element 13 facing these areas 11a7 and 11a8, magnetized areas 13a1 and 13a2 are buried. The magnetized regions 11a7 and 11a8 in the circular disks act with the magnetized regions 13a1 and 13a2 of the base ring together such that the annular disks 11a2 and 11a3 interact with the base ring 13a via axial magnetic forces, wherein the term "axially" here on the common axis of symmetry of the guide element 11 and. Control 13 refers. Thus, the magnetic bearing of the control element 13 against the guide member 11 constraints in such a way that the control element 13 can neither axially move out of the guide member 11 still tilt in this. The above-mentioned mechanical emergency storage is claimed only in exceptional operating conditions that overwhelm the magnetic storage by the interaction of the magnetized areas 11a7 and 11a8 with the magnetized areas 13a1 and 13a2.

The magnetized region 13b, which is recessed in the base ring 13a of the control, forms a magnetic gap with the magnetic coil 11b. The magnetized region 11a7 forms a magnetic gap with the magnetized region 13a1. The magnetized region 11a8 forms a magnetic gap with the magnetized region 13a2.

The area 13c reflecting the particle beam and thus impermeable receives its reflective property by means of a coating 13c1 applied on one side.

In the in FIG. 3 In the embodiment shown, optionally, the magnetized regions 13b buried in the base ring 13a of the control element 13 may be additionally secured by a layer or winding of high strength material (such as CFIC or a woven fabric) which provides radially outward movement of the magnetized regions Prevent 13b from the base ring 13a out. In this direction, in operation on the magnetized regions 13b, the centrifugal force, which can be significant, since permanent magnetic materials usually have a high density.

FIG. 4 shows the chopper in a three-dimensional representation. It can be seen particularly clearly that the particle-beam-reflecting regions 13c in operation within the gap 11a6 between the extensions 11a4 and 11a5 of the annular discs 11a2 and 11a3 of the main body 11 a of the guide member 11 rotate.

Claims (15)

1. Chopper for a particle beam, characterised by at least one annular guide element (11) and at least one control element (13) for the particle beam, which is mounted against the guide element in such a way that at least one receiving point on the control element may circulate along a circumference of the guide element.
2. Chopper according to claim 1, characterised by a circular guide element.
3. Chopper according to one of claims 1 to 2, characterised by a chopper wheel as a control element.
4. Chopper according to claims 1 to 3, characterised by an annular, particularly a circular control element.
5. Chopper according to one of claims 1 to 4, characterised in that the control element has at least one reflective area (13c) for the particle beam.
6. Chopper according to one of claims 1 to 5, characterised in that the control element has at least one helical hole.
7. Chopper according to one of claims 1 to 6, characterised by a neutron beam as a particle beam.
8. Chopper according to one of claims 1 to 7, characterised by the control element being mounted in such way that the receiving point may circulate along an inner circumference of the guide element.
9. Chopper according to one of claims 1 to 8, characterised by a magnetic mounting of the control element against the guide element.
10. Chopper according to claim 9, characterised in that the guide element and the control element each have a magnetised area made in such a way that these magnetised areas repel each other at the point on the circumference of the receiving point, at which they come closest to each other.
11. Chopper according to claims 9 to 10, characterised in that the magnetic mounting has constraints in such a way that the control element may not move out of the guide element axially or bend out of line in it.
12. Chopper according to one of claims 9 to 11, characterised in that the guide element has means for producing a magnetic travelling field.
13. Chopper according to claim 12, characterised by means for impressing a time dependence on the magnetic travelling field.
14. Chopper according to claims 12 to 13, characterised in that at least one temporarily or permanently magnetised area of the guide element, which belongs to the magnetic mounting of the control element against the guide element, is also an element for producing the magnetic travelling field.
15. Chopper according to one of claims 12 to 14, characterised in that the travelling field is vertical to the field of the magnetic mounting.

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