Abstract:
The invention relates to an HF resonator comprising a cylindrical cavity made of a dielectric material. An inner face of the cavity has an electrically conductive coating which is divided into a first inner coating and a second inner coating by an electrically insulating gap that encircles a lateral face of the cavity in an annular manner. An outer face of the cavity has an electrically conductive first outer coating and an electrically conductive second outer coating. The first outer coating and the second outer coating are electrically insulated from each other. The HF resonator comprises a device that is provided for applying a high-frequency electric voltage between the first outer coating and the second outer coating.

Description:
This application is the National Stage of International Application No. PCT/EP2012/067266, filed Sep. 5, 2012, which claims the benefit of German Patent Application No. DE 10 2011 083 668.3, filed Sep. 29, 2011. The entire contents of these documents are hereby incorporated herein by reference. 
     BACKGROUND 
     The present embodiments relate to a radio frequency (RF) resonator. 
     Radio-frequency electromagnetic oscillations may be excited in RF resonators. RF resonators may also be designated as cavity resonators. RF resonators are used, for example, in particle accelerators for accelerating electrically charged particles. 
     In order to excite a radio-frequency electromagnetic oscillation in an RF resonator, it is known to generate a radio-frequency power using a klystron or a tetrode, for example, and to transport the power by a cable or a waveguide to the RF resonator and to couple the power into the RF resonator at the RF resonator via a radiation window or an RF antenna. However, very high RF powers may not be obtained with this type of excitation. 
     EP 0 606 870 A1 discloses equipping an RF resonator with a conductive wall with a plurality of solid-state transistors for inducing a radio-frequency electric current flow in the wall of the RF resonator and thereby exciting a radio-frequency electromagnetic oscillation in the RF resonator. The excitation of the current flow takes place by the application of a radio-frequency electrical voltage via an electrically insulating slot in the wall of the RF resonator. 
     Use of RF resonators in particle accelerators for accelerating electrically charged particles includes evacuation of the RF resonator to a very low pressure. Electrically insulating slots filled with dielectric material in otherwise conductive walls of an RF resonator may be sealed only with difficulty and in a complex manner. 
     SUMMARY AND DESCRIPTION 
     The scope of the present invention is defined solely by the appended claims and is not affected to any degree by the statements within this summary. 
     The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, an RF resonator that may be better evacuated is provided. 
     An RF resonator includes a cylindrical cavity composed of a dielectric material. An inner side of the cavity has an electrically conductive coating that is subdivided into a first inner coating and a second inner coating by an electrically insulating gap extending circumferentially around a lateral surface of the cavity in ring-shaped fashion. An outer side of the cavity has an electrically conductive first outer coating and an electrically conductive second outer coating. The first outer coating and the second outer coating are electrically insulated from one another. The RF resonator includes a device provided for applying a radio-frequency electrical voltage between the first outer coating and the second outer coating. Advantageously, the cylindrical cavity of this RF resonator may be evacuated in a simple manner and does not have any perforations that are problematic to seal (e.g., any metal-ceramic connections that are difficult to seal). Advantageously, the device of the RF resonator may capacitively excite a radio-frequency electromagnetic oscillation in the RF resonator via the conductive outer and inner coatings. 
     In one embodiment of the RF resonator, the gap extending circumferentially in ring-shaped fashion is oriented perpendicularly to a longitudinal direction of the cylindrical cavity. Advantageously, the RF resonator has a mirror symmetry and rotational symmetry, which enables an excitation of symmetrical oscillation modes. 
     In another embodiment of the RF resonator, the first outer coating and the second outer coating each extend circumferentially around the lateral surface of the cavity in ring-shaped fashion. Advantageously, the outer side of the RF resonator then also has a mirror symmetry and rotational symmetry, which enables an excitation of symmetrical oscillation modes. 
     The first outer coating may be adjacent to the first inner coating in a direction oriented perpendicularly to the lateral surface of the cavity. Advantageously, there is then a strong capacitive coupling between the first outer coating and the first inner coating. 
     The second outer coating may be adjacent to the second inner coating in a direction oriented perpendicularly to the lateral surface of the cavity. Advantageously, there is then a high capacitive coupling between the second outer coating and the second inner coating. 
     In one development of the RF resonator, the device includes a solid-state power transistor. Advantageously, with a solid-state power transistor, the RF power to be coupled into the RF resonator may be generated close to the coupling-in location. 
     In one development of the RF resonator, the device includes a plurality of solid-state power transistors arranged around the lateral surface of the cavity in ring-shaped shaped fashion. Advantageously, the provision of a plurality of solid-state power transistors enables the excitation of a particularly high RF power in the RF resonator. 
     In one embodiment of the RF resonator, the dielectric material is a glass or a ceramic. Advantageously, glass and ceramic have mechanical properties suitable for use as a vacuum vessel. 
     The cavity may have a circular-cylindrical shape. Advantageously, a cavity embodied in circular-cylindrical fashion enables an excitation of oscillation modes suitable for accelerating charged particles. 
     In one embodiment, the cavity is configured to be evacuated to a reduced air pressure compared with the surroundings of the cavity. Advantageously, the RF resonator may be used for accelerating electrically charged particles. 
     A particle accelerator according to one or more of the present embodiments for accelerating electrically charged particles includes an RF resonator of the type mentioned above. Advantageously, the RF resonator in this particle accelerator may be evacuated to a low pressure and has no seams that are difficult to seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a section through one embodiment of an RF resonator; and 
         FIG. 2  shows a section through a wall portion of one embodiment of the RF resonator. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows one embodiment of an RF resonator  100  in a highly schematic illustration. A radio-frequency electromagnetic oscillation mode may be excited in the RF resonator  100 . The RF resonator  100  may serve, for example, for accelerating electrically charged particles in a particle accelerator. 
     The RF resonator  100  includes a cavity  200 . The cavity  200  is embodied as a hollow cylinder and has a circular-disk-shaped first cover surface  210 , a circular-disk-shaped second cover surface  220  and a lateral surface  230  connecting the first cover surface  210  to the second cover surface  220 . In the illustration in  FIG. 1 , the cavity  200  is cut on the plane of the drawing. Consequently,  FIG. 1  illustrates only one half of the cavity  200 . 
     The cavity  200  embodied in hollow-cylindrical fashion defines a longitudinal direction  201  and a radial direction  202  that is oriented perpendicularly to the longitudinal direction  201 . The first cover surface  210  and the second cover surface  220  are each oriented perpendicularly to the longitudinal direction  201 . The lateral surface  230  of the cavity  200  extends between the first cover surface  210  and the second cover surface  220  along the longitudinal direction  201 . 
     In alternative embodiments, the first cover surface  210  and the second cover surface  220  may also be embodied differently than in circular-disk-shaped fashion. By way of example, the cover surfaces  210 ,  220  may each have a rectangular shape or an elliptical shape. 
     The cavity  200  consists of an electrically insulating dielectric material. In one embodiment, the cavity  200  consists of a glass or a ceramic. Advantageously, glass and ceramic materials are strong enough to withstand a high pressure difference between an interior of the cavity  200  and the surroundings of the cavity  200 . 
     The cavity  200  of the RF resonator  100  completely encloses a hollow space and may have no seams that are difficult to seal. Also, the cavity  200  of the RF resonator  10  may have no metal-ceramic transitions. This enables the cavity  200  to be evacuated to a reduced pressure compared with an air pressure in the surroundings of the cavity  200 . For the purpose of evacuating the cavity  200 , the cavity  200  may have one or a plurality of suitable flanges. The first cover surface  210  and the second cover surface  220  of the cavity  200  may also have suitable openings or windows through which a beam of charged particles may pass into the interior of the cavity  200  and may exit from the interior of the cavity  200 . 
     The cavity  200  has an inner side  240  facing the hollow space enclosed by the cavity  200 . The cavity  200  has an outer side  250  facing the surroundings of the cavity  200 . 
     An electrically conductive inner coating  300  is arranged on the inner side  240  of the cavity  200 . The electrically conductive inner coating  300  may include a metal, for example. The inner coating  300  is subdivided into a first inner coating  310  and a second inner coating  320 . An electrically insulating inner gap  330  is arranged between the first inner coating  310  and the second inner coating  320 . The inner gap electrically insulates the first inner coating  310  from the second inner coating  320 . In the region of the inner gap  330 , no conductive coating is provided on the inner side  240  of the cavity  200 . 
     In one embodiment, the inner gap  330  is arranged in a manner extending circumferentially on the lateral surface  230  of the cavity  200  in ring-shaped fashion. In this case, the inner gap  330  may be oriented perpendicularly to the longitudinal direction  201  of the cavity  200  and thus parallel to the cover surfaces  210 ,  220 . In one embodiment, the inner gap  330  is arranged centrally between the first cover surface  210  and the second cover surface  220 . 
     The first inner coating  310  covers the inner side  240  of the first cover surface  210  and the inner side  240  of a portion of the lateral surface  230  that is adjacent to the first cover surface  210 . The second inner coating  320  covers the inner side  240  of the second cover surface  220  and the inner side  240  of a portion of the lateral surface  230  that is adjacent to the second cover surface  220 . 
     In the longitudinal direction  201 , the inner gap  330  may be made very narrow. For example, the width of the inner gap  330  in the longitudinal direction  201  may be small compared with a length of the cavity  200  in the longitudinal direction  201  and small compared with a wavelength of a radio-frequency oscillation mode that may be excited in the RF resonator  100 . 
     An electrically conductive outer coating  400  is arranged on the outer side  250  of the cavity  200 . The outer coating  400  may consist of a metal, for example. The outer coating  400  includes a first outer coating  410  and a second outer coating  420 . An outer gap  430  is arranged between the first outer coating  410  and the second outer coating  420 . In the region of the outer gap  430 , no electrically conductive coating is provided on the outer side  250  of the cavity  200 . The outer gap  430  electrically insulates the first outer coating  410  and the second outer coating  420  from one another. 
       FIG. 2  shows a section through a portion of the lateral surface  230  of the cavity  200  of the RF resonator  100  in the region of the inner gap  330  and of the outer gap  430 . The outer gap  430  is situated at the same position as the inner gap  330  in the longitudinal direction  201 . In the radial direction  202 , the outer gap  430  is adjacent to the inner gap  330 . The outer gap  430  is arranged on the outer side  250  of the lateral surface  230  in a manner extending circumferentially in a ring-shaped fashion. If the inner gap  330  is situated in the center between the first cover surface  210  and the second cover surface  220  in the longitudinal direction  201  of the cavity  200 , then the outer gap  430  may also be arranged centrally between the first cover surface  210  and the second cover surface  220 . The width of the outer gap  430  in the longitudinal direction  201  may substantially correspond to the width of the inner gap  330  in the longitudinal direction  201 . 
     The first outer coating  410  and the second outer coating  420  are each arranged on the outer side  250  of the lateral surface  230  in a manner extending circumferentially in ring-shaped fashion. In this case, the outer coatings  410 ,  420  embodied in ring-shaped fashion may be oriented perpendicularly to the longitudinal direction  201  of the cavity  200 . The width of the first outer coating  410  in the longitudinal direction  201  and the width of the second outer coating  420  in the longitudinal direction  201  may correspond approximately to the width of the outer gap  430  in the longitudinal direction  201  of the cavity  200 . The first outer coating  410  and the second outer coating  420  may also have a larger width or a smaller width than the outer gap  430  in the longitudinal direction  201 . In one embodiment, the width of the first and second outer coatings  410 ,  420  in the longitudinal direction  201  is small relative to a wavelength of an electromagnetic oscillation mode that may be excited in the cavity  200 . 
     The first outer coating  410  is insulated from the first inner coating  310  by the dielectric lateral surface  230 . The second outer coating  420  is insulated from the second inner coating  320  by the dielectric lateral surface  230 . The first inner coating  410 , the dielectric lateral surface  230  and the first inner coating  310  form a first capacitor. The second outer coating  420 , the dielectric lateral surface  230  and the second inner coating  320  form a second capacitor. The first and second capacitors bring about a capacitive coupling between the first outer coating  410  and the first inner coating  310  and between the second outer coating  420  and the second inner coating  320 . An electrical voltage applied between the first outer coating  410  and the second outer coating  420  is coupled capacitively into the first inner coating  310  and the second inner coating  320 , such that an electrical voltage applied between the first outer coating  410  and the second outer coating  420  brings about a substantially identical electrical voltage between the first inner coating  310  and the second inner coating  320 . 
     The RF resonator  100  includes a drive device  500  that is provided for coupling radio-frequency electromagnetic power into the cavity  200  of the RF resonator  100 . The drive device  500  is configured to apply a radio-frequency electrical voltage between the first outer coating  410  and the second outer coating  420 . The drive device  500  may include a solid-state power transistor or some other solid-state switch. In one embodiment, the drive device  500  includes a plurality of solid-state power transistors arranged in a ring-shaped manner in the region of the outer gap  430  in a manner extending circumferentially on the outer side  250  of the lateral surface  230  of the cavity  200 . 
     If the drive device  500  applies a radio-frequency electrical AC voltage between the first outer coating  410  and the second outer coating  420 , then a radio-frequency electrical AC voltage also occurs between the first inner coating  310  and the second inner coating  320  owing to the capacitive couplings between the outer coatings  410 ,  420  and the inner coatings  310 ,  320 . In the first inner coating  310  and the second inner coating  320 , the radio-frequency electrical voltage coupled in excites a radio-frequency electric current flow. 
     If the frequency of the AC voltage applied by the drive device  500  between the first outer coating  410  and the second outer coating  420  corresponds to a resonant frequency of the RF resonator  100 , then the current flow induced in the inner coatings  310 ,  320  brings about an excitation of a resonant radio-frequency oscillation mode in the interior of the cavity  200 . 
     Consequently, the drive device  500  allows radio-frequency electromagnetic power to be coupled capacitively into the cavity  200  of the RF resonator  100 , in order to excite and amplify a resonant radio-frequency oscillation in the interior of the cavity  200 . 
     Advantageously, the cavity  200  of the RF resonator  100  simultaneously serves as a vessel to be evacuated and as a carrier for the electrically conductive inner coating  300 . By virtue of the possibility of a capacitive excitation, the cavity  200  does not require any electrically conductive perforations and therefore also does not require any metal-ceramic transitions that are difficult to seal. 
     Although the invention has been more specifically illustrated and described in detail by the exemplary embodiments, the invention is not restricted by the examples disclosed. Other variations may be derived therefrom by a person skilled in the art, without departing from the scope of protection of the invention. 
     It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification. 
     While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.