Vacuum Capacitor

Abstract

To provide an electrode capable of reaching higher voltage, and a vacuum capacitor provided with the electrode.SOLUTION: An electrode unit for a vacuum capacitor is provided with a belt-like capacitor plate having height H. The belt-like capacitor plate is wound in a spiral shape with a maximum diameter as Dmax and a constant distance between continuing rotations. The belt-like capacitor plate includes a first longitudinal edge fitted to a support part and a second longitudinal edge. The second longitudinal edge is released, and the first longitudinal edge and the second longitudinal edge are connected by an inclined edge part so that the first longitudinal edge is longer than the second longitudinal edge at an outside end part of the spiral. The inclined edge part forms with a longitudinal axis of the belt-like capacitor plate an angle α equal to or smaller than angle αmax=(45° π / 180°) .SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of vacuum capacitors. More precisely, in a first aspect, the present invention relates to an electrode unit for a vacuum capacitor. This electrode unit comprises a support part made of a highly thermally conductive material, such as copper, and spirally wound strip-shaped capacitor plates made of a high-melting-point metal, such as stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel®, titanium, chromium, or an alloy thereof. The electrode unit of the present invention makes it possible to reach higher voltages inside the vacuum capacitor. In a second aspect, the present invention relates to a vacuum capacitor comprising at least one electrode unit according to the present invention. [Background technology]

[0002] Vacuum capacitors are well known in the art and are used in applications where both high frequency and high power are required. Common applications include, for example, oscillator circuits for use in high power radio frequency transmission, and high frequency power supplies for use in the manufacture of semiconductors, solar panels, and flat panel displays.

[0003] As mentioned above, vacuum capacitors are commonly used in semiconductor industry applications, such as plasma coating and etching processes powered by 27.12 MHz, 13.56 MHz, 6.78 MHz, or other radio frequency sources. Very commonly, vacuum capacitors are used as tuning elements, integrated into impedance matchers or other devices that ensure optimal power transfer from a radio frequency generator (with a 50 Ω output impedance) to a dynamic load (i.e., variable impedance) plasma processing chamber. It is desirable to be able to use these impedance matchers at increasingly higher powers, resulting in higher operating voltages. Power density inevitably increases because higher output must be achieved without increasing the size of the capacitor or the device in which it is located. This trend is exacerbated by the fact that power supplies at frequencies below 6.78 MHz and even below 4 MHz are becoming more prevalent, resulting in higher voltages across vacuum capacitors even when used in power applications of the same nominal power due to their higher impedance at these frequencies.

[0004] State-of-the-art vacuum capacitors contain two or more copper electrodes or electrode units separated by a dielectric medium. Copper is generally viewed as a good material for the electrodes or electrode units due to its low electrical losses. Even with very high RF currents, vacuum capacitors generate only modest heat, which can be easily transported away from the electrodes to the housing collar by thermal conduction and then from the housing to the surrounding atmosphere by simple convection and radiation. However, vacuum capacitors may be limited by the current they can sustain before reaching a critical temperature or by the signal voltage they can handle (depending on the application's power signal frequency or duty cycle, either voltage or current may be the most important limiting factor). State-of-the-art vacuum capacitors can withstand approximately 20-25 kV when the copper electrodes are separated by only 1 mm in vacuum. By increasing the electrode separation, the voltage can be further increased, but the size of the copper vacuum capacitor would increase.

[0005] As already mentioned above, copper is the preferred electrode material because it allows for very high current ratings for vacuum capacitors. Most vacuum capacitors are rated for a nominal current of 13.56 MHz. For example, the rated current value is 94 A at 13.56 MHz. RMS However, depending on the geometry of the capacitor sub-components (electrodes, collar, bellows, etc...) and the heat transfer arrangement, the value may be significantly higher or significantly lower. The rated current is I for a specific frequency or over a frequency range. max The frequency curve is given. The frequency of 13.56 MHz is the standard for industrial processes. However, sometimes other frequencies, such as 6.78 MHz, 2 MHz, 400 kHz, or even other frequencies, are used in various applications. The rated current is different at these other frequencies due to the frequency dependence of the skin effect phenomenon, which results in a frequency-dependent electrical resistivity of copper parts.

[0006] Besides copper, other metals for vacuum capacitor electrodes are known to provide satisfactory properties. For example, WO 2012 / 000532 proposes aluminum electrodes for vacuum capacitors with improved voltage resistance. Another example is found in JP 11-273998 A, which discloses high-melting-point hard materials such as stainless steel as alternative electrode materials.

[0007] Materials for vacuum capacitor electrodes other than copper can improve the high-voltage performance of vacuum capacitors. Improving the voltage performance of a capacitor without necessarily increasing its size or decreasing its capacitance value is an important feature, so replacing copper with other materials can be advantageous. This is particularly advantageous in applications where voltage is critical rather than current critical, such as low-duty-cycle pulsed power or continuous-wave power at frequencies substantially lower than 13.56 MHz. This is due to a better overall ratio of heat generated to heat removed when operating with low-duty-cycle pulsed power, and a more favorable skin effect coefficient at lower frequencies.

[0008] To make vacuum capacitors compact, i.e., to maximize the capacitance-generating surface within a given volume, the electrodes inside the vacuum enclosure are typically of two types: concentric cylinders, as disclosed, for example, in U.S. Pat. No. 3,611,075, or alternating spiral electrodes, as presented in Swiss Patent No. 598,687. Spiral electrodes have the added advantage that the pair of connecting electrodes is self-centering, meaning that the distance between the alternating electrode surfaces is exactly equal throughout.

[0009] In the case of a vacuum capacitor, the dielectric medium is a vacuum. Vacuum capacitors are typically placed in a high vacuum (10 -6 Torr) or ultra-high vacuum (10 -9The vacuum is maintained inside a hermetic housing, also referred to in this application as an enclosure. A typical housing may include an insulating element, often a ceramic cylinder, tightly bonded to a metal collar, typically made of copper, to ensure a hermetic seal so that a high vacuum inside the enclosure can be maintained throughout the capacitor's operating life. The most common joining technique is a brazing process, which may require brazing temperatures of up to 800°C depending on the brazing material. This brazing step has previously prevented the use of electrode units with support parts made of a highly thermally conductive material, such as copper, and spirally wound strip capacitor plates made of a high-melting-point material, such as stainless steel, molybdenum, tantalum, or tungsten. If the spirally wound strip capacitor plates of a known electrode unit made of copper are simply replaced with capacitor plates made of a high-melting-point material, the capacitor will disintegrate during assembly of the vacuum capacitor, specifically during the brazing process. Such electrode units, each a vacuum capacitor, cannot be used reliably due to the disintegration.

[0010] However, as mentioned above, electrode units for vacuum capacitors featuring strip capacitor plates made of a high-melting-point material, and vacuum capacitors including one or more such electrode units, have numerous advantages. It is therefore an object of the present invention to propose a novel electrode unit, which avoids the risk of collapse during the brazing step of the vacuum capacitor assembly process. It is also an object of the present invention to propose a vacuum capacitor that can withstand higher operating voltages thanks to an electrode unit with strip capacitor plates made of a high-melting-point material. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2012 / 000532 Brochure [Patent Document 2] Japanese Patent Application Publication No. 11-273998 [Patent Document 3] U.S. Patent No. 3,611,075 [Patent Document 4] Swiss Patent No. 598687 Summary of the Invention [Problem to be solved by the invention]

[0012] The elements of the present invention therefore propose a new electrode unit for a vacuum capacitor and a new vacuum capacitor, by which the above-mentioned drawbacks of known systems are completely overcome or at least significantly reduced.

[0013] The elements of the present invention propose, in particular, an electrode unit for a vacuum capacitor, comprising a support part made of a material with high thermal conductivity and a spirally wound strip-shaped capacitor plate made of a high-melting-point metal, which makes it possible to avoid collapse of the electrode unit during the brazing step of the assembly process of the vacuum capacitor. [Means for solving the problem]

[0014] According to the invention, this feature is realized by the elements of the two independent claims. Further advantageous embodiments follow from the dependent claims and the description.

[0015] In particular, the object of the invention is to provide an electrode unit for an electric vacuum capacitor, comprising strip-shaped capacitor plates having a height H, the strip-shaped capacitor plates having a maximum diameter D maxand the distance between successive turns is constant and the strip capacitor plate is wound in a spiral, the strip capacitor plate including a first longitudinal edge attached to a support portion and a second longitudinal edge, the second longitudinal edge being free, and at an outer end of the spiral the first longitudinal edge and the second longitudinal edge are connected by an inclined edge such that the first longitudinal edge is longer than the second longitudinal edge, the inclined edge being inclined with the longitudinal axis of the strip capacitor plate by an angle α max This is achieved by the electrode units forming an angle α of less than or equal to (45°·π / 180°).

[0016] The inventors have determined that the angle α between the beveled edge of the capacitor plate and its longitudinal axis is α max We have found that by setting α = (45°·π / 180°) or less, it is possible to provide an electrode unit having a support plate made of a highly thermally conductive material such as copper, silver, aluminum, or their alloys, and strip capacitor plates made of a high-melting-point metal such as stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel®, titanium, chromium, or their alloys, which does not collapse during the brazing process used in the manufacturing process of a vacuum capacitor. This is highly advantageous because the highly thermally conductive support plate allows optimal heat transport, while a capacitor plate made of one of the listed materials allows a higher voltage to be reached before vacuum breakdown occurs. Simulations have shown that the von Mises stress due to temperature fluctuations, a cause of failure of electrode units known in the art, can be avoided or at least significantly reduced by an appropriate value of α.

[0017] In a first preferred embodiment of the present invention, the angle α is min =γ tan -1 (2H / (π D max)), where γ is a real number greater than or equal to 1.0. This angle ensures that the outermost spiral extends to the full height H of the other turns before reaching half a turn, ensuring sufficient connection with the counter electrode unit. The counter electrode unit is therefore also called the connecting electrode unit.

[0018] A coefficient γ greater than 1.0 can be advantageously selected to optimize the shape of the outermost turns of the capacitor plates in order to utilize the available volume for the electrode unit that will be placed inside. Indeed, vacuum capacitors (for which these electrode units are intended) are typically required to have a small volume, making them easier to pump down. Another requirement for small-volume vacuum capacitors is that they are often incorporated into equipment components, such as impedance matchers, that themselves have limited volume. Therefore, the volume inside the vacuum capacitor enclosure should be used efficiently. Selecting a coefficient γ greater than 1 allows the otherwise wasted volume to be filled with additional metal that creates capacitance.

[0019] In a second preferred embodiment, the support portion is made of copper, silver, aluminum, or an alloy thereof, and the strip capacitor plates are made of stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel®, titanium, chromium, or an alloy thereof, thereby providing an electrode unit with a high heat flow thanks to the copper support portion and a high vacuum breakdown voltage thanks to the material of the strip capacitor plates, without the risk of collapse during assembly of the vacuum capacitor.

[0020] In another preferred embodiment of the present invention, α max is equal to (35°·π / 180°), which ensures that the deformation of the strip capacitor plates of the electrode unit is small during the brazing step in the manufacturing process of the vacuum capacitor.

[0021] In another preferred embodiment of the present invention, α max is equal to (23°·π / 180°). The deformation of the strip capacitor plates of the electrode unit during the brazing step of the manufacturing process of the vacuum capacitor is further reduced. This allows for the manufacture of vacuum capacitors with higher precision. An angle α selected equal to or less than (23°·π / 180°) is particularly preferred, as in this case the thermal stresses generated during the manufacture of the electrode unit can be kept small even at high brazing temperatures, which allows for a more flexible brazing process.

[0022] This can be particularly advantageous when the electrode unit is incorporated into a vacuum capacitor in a manufacturing process that requires multi-step brazing, including a very high temperature first brazing step (e.g., using a palladium alloy braze) at approximately 930°C, a second brazing step (using a copper-silver alloy braze) at approximately 800°C, and an additional brazing step (using a suitable indium-copper-silver alloy braze) at approximately 705°C. The brazing furnace temperatures described above are indicative and valid for specific braze compositions. Importantly, the furnace temperature must reach a value above the liquidus temperature of the braze for each braze step, and subsequent brazing steps must be performed at lower temperatures so as not to melt the braze used in the previous step. Most brazes have a melting temperature range where solid and liquid phases can coexist. For example, the aforementioned brazing temperature of 705°C is appropriate for an indium-copper-silver brazing alloy of composition In 14.5%-Ag 24%-Cu 61.5% having a solidus temperature of 630°C and a liquidus temperature of 705°C. Thus, heating the brazing furnace to 705°C allows the brazing material to fully liquefy and flow over the surfaces to be brazed together, where it solidifies upon cooling, ensuring a good metallurgical bond. Note that in practice, a slightly higher temperature of 705°C may be selected to account for possible non-uniformities in industrial furnaces and to account for possible tolerances in temperature control equipment.

[0023] To avoid melting of the brazing filler metal used in the preceding step (800°C, continuing to refer to the above example), it is important that both the solidus and liquidus temperatures of the brazing filler metal in that previous step exceed 705°C. In other words, the melting ranges of the brazing filler metals used in the two brazing steps must not overlap with each other. A multi-step brazing process can be advantageous for the manufacturing process of vacuum capacitors, since the electrode units (capacitor plates and support parts) can be brazed independently in a first step, and then, during one or more subsequent steps, the electrode units can undergo important surface optimization steps (such as cleaning, polishing, quality assessment, etc.) before being further brazed to the metal collar of the future vacuum capacitor housing, and finally, the internal volume of the housing is pumped down to create the vacuum dielectric medium of the vacuum capacitor. With the aim of having a qualitatively satisfactory and durable brazed joint for a vacuum capacitor, the melting ranges (i.e., the distance from the solidus to the liquidus temperature) of the brazing filler metals used are selected so that they do not overlap. The above paragraph relates to the electrode units described above. It can now be seen why choosing a capacitor plate angle α of less than or equal to (23°·π / 180°) is beneficial, since it allows for multiple brazing steps at increasingly higher temperatures. This is because smaller angle values ​​advantageously lead to lower von Mises stresses, despite the fact that much larger temperature cycles are involved.

[0024] In yet another preferred embodiment of the invention, the beveled edges are rounded at the transition to the first longitudinal edge and / or the second longitudinal edge, which makes it possible to avoid sharp edges or spikes at the transition between the beveled edges and the longitudinal edges of the capacitor plates that may promote breakdown of the electric field in a vacuum.

[0025] In a further preferred embodiment of the invention, the support part comprises a spiral guide edge arranged in the space formed by two successive turns of the strip capacitor plate, the width of the guide edge corresponding to the distance between two successive turns of the strip capacitor plate, which makes it possible to easily attach the capacitor plate to the support part while ensuring that the distance between two successive turns remains constant.

[0026] In yet another preferred embodiment of the present invention, the strip capacitor plates are attached to the support portion by brazing.

[0027] The object of the present invention is also achieved by a vacuum capacitor comprising an enclosure for containing a vacuum dielectric medium, and a first electrode unit and a second electrode unit separated by the vacuum dielectric medium, the enclosure including a first conductive collar in electrical contact with the first electrode unit and a second conductive collar in electrical contact with the second electrode unit, the first conductive collar and the second conductive collar being separated by an insulating element of the enclosure, and at least one of the first electrode unit or the second electrode unit being an electrode unit of the present invention.

[0028] Thanks to electrode units with strip capacitor plates made of high-melting-point metals, vacuum capacitors with higher operating voltages can be obtained. The maximum angle of the beveled edges of the strip capacitor plates of the electrode units ensures that the strip capacitor plates do not collapse during the necessary brazing step of the metal collar to the insulating housing of the capacitor. Until now, this collapse of the strip capacitor has been the reason why vacuum capacitors including electrode units with spirally wound strip capacitor plates made of high-melting-point materials such as stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel®, titanium, chromium, or alloys thereof have not been available. A further advantage of the vacuum capacitor according to the present invention is provided by the combination of capacitor plates made of a high-melting-point material with support plates made of a highly thermally conductive metal, which allows for the high operating currents required in many applications of vacuum capacitors.

[0029] In a first preferred embodiment of this aspect of the invention, the vacuum capacitor comprises two connecting electrode units according to the invention, and the spiral of the strip capacitor plates is chiral, which makes it possible to obtain a vacuum capacitor with spirally intertwined capacitor plates, with a first capacitor plate of one electrode unit being in the space between two successive turns of the capacitor plates of the other electrode unit.

[0030] In another preferred embodiment of this aspect of the invention, the strip capacitor plate and the support plate of the at least one electrode unit are attached to one another using a first brazing material, and the first conductive collar and the second conductive collar are each attached to opposite ends of the insulating element of the enclosure using a second brazing material, the first brazing material and the second brazing material being selected to have non-overlapping melting ranges.

[0031] This advantageously makes it possible to include important surface optimization steps (such as cleaning, polishing, quality assessment, etc.) between successive brazing steps. Such optimization steps may be required to achieve the best possible voltage compatibility of the vacuum capacitor during operation. Indeed, the electric field breakdown threshold in vacuum depends primarily on the electrode surface quality (and a good vacuum level between these surfaces).

[0032] In another preferred embodiment of this aspect of the invention, the first brazing material has a melting temperature as high as the second brazing material, which is advantageous because it ensures that the first brazing material does not melt during the process of attaching the conductive collar to the insulating element.

[0033] In an even further preferred embodiment of this aspect of the invention, the strip capacitor plates and the support plate of one electrode unit are attached to each other using a first brazing material, the strip capacitor plates and the support plate of the other electrode unit are attached to each other using a second brazing material, and the first conductive collar and the second conductive collar are each attached to opposite ends of the insulating element of the enclosure using a third brazing material, and the first brazing material, the second brazing material, and the third brazing material are selected to have non-overlapping melting ranges.

[0034] This advantageously allows flexibility in successive manufacturing steps, quality assurance between those steps, and reliable vacuum-tight metal-metal and metal-insulator joints (with the insulating parts of the enclosure).

[0035] In another preferred embodiment of this aspect of the invention, a bellows and movement system is provided to allow the position of at least one of the two electrode units to be changed, thereby making it possible to adjust the capacitance value of the vacuum capacitor by adjusting the overlap of the surfaces of the strip capacitor plates of the electrode units. The movement system may, for example, comprise a simple screw and nut system or another mechanism allowing similar adjustment.

[0036] In another preferred embodiment of this aspect of the invention, the overlap of the faces of the strip capacitor plates of the two electrode units of the vacuum capacitor is fixed, which allows the capacitance value of the vacuum capacitor to be fixed. [Brief explanation of the drawings]

[0037] [Figure 1] 1 is a side perspective view of an electrode unit according to a first embodiment of the present invention. FIG. [Figure 2] 1 is a side view of an electrode unit according to a first embodiment of the present invention. [Figure 3a] FIG. 2 is a top view of two connecting electrode units according to a first embodiment of the present invention. [Figure 3b] FIG. 10 shows the orientation of two connecting electrode units according to the present invention. [Figure 3c] FIG. 1 shows the insertion of two connecting electrode units according to the present invention. [Figure 4] FIG. 10 is a first side view of an electrode unit according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a second side view of the electrode unit according to the second embodiment of the present invention. [Figure 6] 1 is a cross-sectional view of a vacuum capacitor according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] Figure 1 shows a perspective view of an electrode unit 10 according to a first preferred embodiment of the present invention. The electrode unit 10 comprises a strip-shaped capacitor plate 11 wound in a spiral shape around a rotation axis A of a support part 12. As also shown in Figure 3a, the spiral has a maximum diameter D max , with successive turns being equidistant from one another. The distance between two successive turns advantageously exceeds the thickness of the strip capacitor plates 11. This makes it possible to use two connecting electrode units 10, in which the strip capacitors of a first electrode unit are located in the space between successive turns of a second electrode unit. Two connecting electrode units 10 and 10' are shown in Figure 3a. The electrode units 10 and 10' differ in that the helices of the strip capacitor plates 11 and 11' are chiral. This makes it possible to insert the strip capacitor plates of one electrode unit into the space between successive turns of the strip capacitor plates of the other electrode unit, as shown in Figures 3b and 3c, thereby changing the overlap of the capacitor plate surfaces.

[0039] The strip capacitor plate 11 includes a first longitudinal edge 11a attached to the support plate 12 and a second longitudinal edge 11b that is free. At the outer end of the spiral, the strip capacitor plate 11 presents a beveled edge 11c that connects the first longitudinal edge 11a with the second longitudinal edge 11b.

[0040] The support part 12 advantageously comprises a helical guide edge 13 arranged in the space formed by two successive turns of the strip capacitor plate 11. The width of the guide edge 13 corresponds to the distance between two successive turns of the strip capacitor plate 11. The guide edge 13 has the advantage of ensuring that the successive turns of the capacitor plate 11 remain equidistant during assembly of the strip capacitor plate 11 to the support part 12.

[0041] As mentioned above, the vacuum enclosure of a vacuum capacitor must include an insulating piece, most often a cylindrical ceramic that is brazed to two metal collars. It has been observed by the inventors that when attempting to replace the copper strip capacitor plates of electrode units known in the art with strip capacitor plates made of a high melting point material, such as stainless steel, the strip capacitor electrodes collapse during the brazing process, i.e., the distance between successive revolutions changes.

[0042] The inventors have found that the value of angle α, which is the angle formed by the longitudinal axis B of the capacitor plate 11 with the beveled edge 11c, is crucial to being able to have an electrode unit 10 with a support portion 12 made of copper, silver, aluminum, alloys thereof, etc., and strip-shaped capacitor plates 11 made of a high-melting-point material, such as stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel®, titanium, chromium, or alloys thereof, that will not collapse during the thermal cycle of the brazing process used to manufacture vacuum capacitors. Simulations have shown that an appropriate value of α can avoid or at least significantly reduce the von Mises stress caused by temperature fluctuations, a cause of failure of electrode units known in the art. The inventors have found that angle α is critical to being able to have an electrode unit 10 with a support portion 12 made of copper, silver, aluminum, alloys thereof, etc., and strip-shaped capacitor plates 11 made of a high-melting-point material, such as stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel®, titanium, chromium, or alloys thereof, that will not collapse during the thermal cycle of the brazing process used to manufacture vacuum capacitors. Simulations have shown that an appropriate value of α can avoid or at least significantly reduce the von Mises stress, which is a cause of failure of electrode units known in the art, due to temperature fluctuations. max = (45° π / 180°) or less. Preferably, a non-magnetic austenitic stainless steel such as alloy 1.4301 can be used to avoid or minimize parasitic effects due to the strong electromagnetic fields present in typical vacuum capacitor environments. These parasitic effects can lead to overheating or other poor performance of the capacitor in power applications.

[0043] As explained above, the angle α is set to the upper limit α max It is crucial that the angle α is smaller than the angle α min =γ tan -1 (2H / (π D max)), where H is the height of the strip capacitor plates 11. min is advantageous because, before reaching half a turn, the outermost spiral extends to the full height H of the other turns, ensuring a sufficient connection with the counter electrode unit.

[0044] The electrode unit 10 of FIG. 2 shows, for example, an angle of (45°·π / 180°), which is the upper limit of tolerance for stainless steel. Nevertheless, the upper limit α max is slightly different for other materials and may be lower or higher. Knowing now that the value of the angle α is critical, one skilled in the art can determine the exact upper limit α for the material selected for the strip capacitor plates. max It will not be difficult to find.

[0045] Advantageously, the beveled edge 11c has a rounded portion 11d at the transition to the first longitudinal edge 11a. Although such a rounded portion is only provided at the first longitudinal edge 11a in Figures 1 and 2, it can also be provided at the transition to the second longitudinal edge 11b. One or more rounded portions has the advantage of avoiding the formation of sharp edges or spikes that could promote vacuum breakdown.

[0046] 4 and 5 show side views of an electrode unit 20 according to a second preferred embodiment of the present invention. The electrode unit 20 differs from the electrode unit 10 only in the shape of the strip-shaped capacitor plates 21. As shown in FIG. 4, the inclined edges 21c of the capacitor plates 21 form an angle α with their longitudinal axis that is smaller than that in the electrode unit 10. To be precise, the angle α of the electrode unit 20 is (22.5°·π / 180°).

[0047] FIG. 6 shows a cross-sectional view of a vacuum capacitor 30 according to a preferred embodiment of this aspect of the present invention. The vacuum capacitor 30 includes an enclosure 31 for containing a vacuum dielectric medium 32. The enclosure includes a first conductive collar 33 and a second conductive collar 34 separated by an insulating element 35 of the enclosure 31. Typically, the insulating element 35 is made of a ceramic material and has a cylindrical shape. For the manufacturing process, the insulating element 35 is brazed to the metal collars 33, 34 using a second brazing material 39. During this process, a temperature of approximately 800°C is required. Without the use of electrode units according to the present invention, such a temperature would lead to the collapse of the strip-shaped capacitor plates 11, 21 of the electrode units 10, 20. As shown in FIG. 6, the electrode units 10, 20 positioned inside the vacuum dielectric 32 are in electrical contact with the conductive collars 33 and 34, respectively. The vacuum capacitor can be a variable vacuum capacitor in which the overlap of the electrode unit surfaces is adjustable using a moving mechanism 36 and an extendable bellows 37. Since the strip capacitor plates 11, 21 and the support plate 12 of the electrode units 10, 20 are brazed together by means of a first brazing filler metal 38, and the ceramic cylinder 35 also has to be brazed to the metal collars 33, 34 in a vacuum-tight manner using a second brazing filler metal 39, the brazing filler metals 38 and 39 used in the successive brazing steps are preferably selected to have non-overlapping melting ranges. It may also be advantageous to provide two different brazing filler metals for the brazing steps of the two electrode units 10, 20.

[0048] Finally, the above outlines relevant, non-limiting embodiments. It will be apparent to those skilled in the art that modifications to the disclosed, non-limiting embodiments can be made without departing from the spirit and scope thereof. Therefore, the described, non-limiting embodiments should be considered merely illustrative of some of their more prominent features and applications. Other beneficial results can be achieved by applying the non-limiting embodiments in different ways or modifying them in ways known to those skilled in the art. It is particularly important to note that it is not possible to describe all possible embodiments, in particular all possible angles α that make it possible to achieve the objectives of the present invention. Nevertheless, those skilled in the art will know how to adapt the angle α to the material selected for the capacitor plates.

Claims

1. A vacuum capacitor (30), an enclosure (31) for containing a vacuum dielectric medium (32); a first electrode unit (10, 20) and a second electrode unit (10, 20) separated by the vacuum dielectric medium (32); Equipped with the enclosure (31) includes a first conductive collar (33) in electrical contact with the first electrode unit (10, 20) and a second conductive collar (34) in electrical contact with the second electrode unit (10, 20); the first conductive collar (33) and the second conductive collar (34) are separated by an insulating element (35) of the enclosure; At least one of the first electrode unit (10, 20) or the second electrode unit (10, 20) comprises a strip-shaped capacitor plate (11, 21) having a height H; The strip-shaped capacitor plates (11, 21) have a maximum diameter D ｍａｘ and the distance between successive turns is constant and the strip-shaped capacitor plates (11, 21) are spirally wound, and the strip-shaped capacitor plates (11, 21) include first longitudinal edges (11a, 21a) attached to a support portion (12) and second longitudinal edges (11b, 21b), and the second longitudinal edges (11b, 21b) are free; At the outer ends of the spirals, the first longitudinal edges (11a, 21a) and the second longitudinal edges (11b, 21b) are connected by inclined edges (11c, 21c) such that the first longitudinal edges (11a, 21a) are longer than the second longitudinal edges (11b, 21b), and the inclined edges (11c, 21c) form an angle α with the longitudinal axis (B) of the strip-shaped capacitor plates (11, 21). ｍａｘ and forms an angle α of not more than (45° π / 180°), the strip-shaped capacitor plates (11, 21) and the support portion (12) of the at least one electrode unit (10, 20) are attached to each other using a first brazing material (38); the first conductive collar (33) and the second conductive collar (34) are attached to opposite ends of the insulating element (35) of the enclosure (31) using a second brazing material (39), A vacuum capacitor (30) wherein the first brazing material (38) and the second brazing material (39) are selected to have non-overlapping melting ranges.

2. The angle α is an angle α ｍｉｎ = γ tan －１ (2H / (π・D ｍａｘ )) or greater, and γ is a real number greater than or equal to 1.

0.

3. 3. The vacuum capacitor (30) according to claim 1 or 2, wherein the support portion (12) is made of copper, silver, aluminum, or an alloy thereof, and the strip-shaped capacitor plates (11, 21) are made of stainless steel, carbon steel, molybdenum, tantalum, tungsten, nickel, Inconel (registered trademark), titanium, chromium, or an alloy thereof.

4. α ｍａｘ The vacuum capacitor (30) of any one of claims 1 to 3, wherein is equal to (35°·π / 180°).

5. α ｍａｘ The vacuum capacitor (30) of any one of claims 1 to 3, wherein is equal to (23°·π / 180°).

6. 6. A vacuum capacitor (30) according to any one of claims 1 to 5, wherein the beveled edge (11c, 21c) is rounded at the transition to the first longitudinal edge (11a, 21a) and / or the second longitudinal edge (11b, 21b).

7. 7. A vacuum capacitor (30) according to any one of claims 1 to 6, wherein the support portion (12) comprises a spiral guide edge (13) arranged in a space formed by two successive turns of the strip-shaped capacitor plates (11, 21), the width of the guide edge (13) corresponding to the distance between two successive turns of the strip-shaped capacitor plates (11, 21).

8. 8. A vacuum capacitor (30) according to any one of claims 1 to 7, wherein the strip capacitor plates (11, 21) are attached to the support part (12) by brazing.

9. A vacuum capacitor (30) as described in any one of claims 1 to 8, wherein the first electrode unit (10, 20) and the second electrode unit (10, 20) are oriented along two connecting coaxial axes, and the spiral of the strip capacitor plate is chiral.

10. 10. A vacuum capacitor according to any one of claims 1 to 9, wherein the first brazing material (38) has a higher melting temperature than the second brazing material (39).

11. 11. The vacuum capacitor according to claim 1, wherein the strip-shaped capacitor plates (11, 21) and the support portion (12) of one electrode unit (10, 20) are attached to each other using a first brazing filler metal (38), the strip-shaped capacitor plates (11', 21') and the support portion (12) of the other electrode unit (10', 20') are attached to each other using a third brazing filler metal (39), the first conductive collar (33) and the second conductive collar (34) are attached to both ends of the insulating element (35) of the enclosure (31) using a second brazing filler metal (39), and the first brazing filler metal, the second brazing filler metal, and the third brazing filler metal are selected to have melting ranges that do not overlap each other.

12. 12. A vacuum capacitor (30) according to any one of the preceding claims, further comprising a bellows and a movement system for enabling the position of at least one of the two electrode units (10, 20) to be changed.

13. 13. The vacuum capacitor (30) according to any one of claims 1 to 12, wherein the overlap of the faces of the strip-shaped capacitor plates of the two electrode units (10, 20) is fixed.

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