Compact high voltage electrical feedthrough

Abstract

Systems, components, and methods are provided for supplying high voltage into a vacuum chamber. An exemplary feedthrough includes a dielectric flange defining a first side, a second side, and an opening extending from the first side to the second side, and a conductor disposed through the opening and making contact with the dielectric flange on the first side.

Description

[Technical Field]

[0001] [Background technology]

[0002] Increasing energy demand and global climate change require an increased proportion of sustainable energy sources. Fusion energy has the potential to provide a zero-carbon, low-waste energy source that could revolutionize the energy industry. As a fusion fuel, one gram of hydrogen isotope is 16m 3 It can provide the same amount of energy as burning 1000 tonnes of coal.

[0003] In a nuclear fusion reaction, light elements (such as hydrogen) are excited to a point where their nuclei can fuse. The output of this reaction is relatively heavy atomic nuclei and energy. Several methods for generating fusion power have been proposed, but all have failed to operate with a net positive energy output (e.g., a Q factor greater than 1). Thermonuclear fusion technology involves a tokamak configuration, in which a hot plasma confined by a strong external magnetic field is contained within a torus. The International Thermonuclear Experimental Reactor (ITER), based in France, is an example. The goal of the ITER collaboration is to prove that net positive fusion power is technically feasible. It is estimated that a 500 MW input power can be extracted in 6 to 10 minutes. The seven-party collaboration is estimated to cost at least $22 billion. Therefore, there is a need for a compact fusion reactor that can be rapidly constructed and deployed, such as in remote locations or space-based platforms, to meet lower power demands with shorter lead times. Summary of the Invention [Problem to be solved by the invention]

[0004] [Means for solving the problem]

[0005] [Brief explanation of the drawings]

[0006] The foregoing aspects and many of the attendant advantages of the claimed subject matter will become better understood as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of a compact feedthrough configured for an operating voltage of approximately ±300 kVDC, according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram of a compact feedthrough configured for an operating voltage of approximately ±600 kVDC, according to an embodiment of the present disclosure. [Figure 3] 3A-3D are schematic cross-sectional views of the compact feedthrough of FIGS. 1 and 2. FIG. [Figure 4] FIG. 4 is a schematic diagram showing a cross-sectional view of the feedthrough of FIG. 1, including the electric field distribution during operation at about +300 kVDC. [Figure 5] FIG. 5 is a schematic diagram showing a cross-section of the feedthrough of FIG. 1, including the potential distribution during operation at about +300 kVDC. [Figure 6] FIG. 6 is a partial schematic diagram showing a cross-section of the feedthrough of FIG. 1 with simulated trajectories and energy information of electrons in a vacuum during operation of the feedthrough at about +300 kVDC. [Figure 7] FIG. 7 is a partial schematic diagram showing a cross-sectional view of the feedthrough of FIG. 1 with simulated trajectories and energy information of secondary electrons in a vacuum during operation of the feedthrough at about +300 kVDC. DETAILED DESCRIPTION OF THE INVENTION

[0007] The detailed description set forth below in connection with the accompanying drawings, in which like numerals refer to like elements, is intended to describe various embodiments of the present disclosure and is not intended to represent the only embodiment. Each embodiment described in the present disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise aspects disclosed.

[0008] As described in more detail below, the present disclosure provides examples of compact bushings and other components compatible with vacuum systems (e.g., ultra-high vacuum) that incorporate insulating or dielectric materials. The insulating or dielectric materials can be structured to reduce the likelihood of surface flashover during operation at high voltages on the order of hundreds of kilovolts. The structure of the dielectric material on the vacuum side, also referred to as the first side, is configured to reduce the number and energy of electrons emitted from the conductor into the vacuum (e.g., by field emission) and to reduce the number and energy of secondary electrons re-emitted from the surface of the dielectric as a result of electron impact.

[0009] As described in detail with reference to the exemplary embodiment of Example 1, embodiments of the present disclosure are directed to compact nuclear fusion systems. However, it is believed that the structures, components, and systems described herein are equally applicable to other low-pressure systems. For example, systems incorporating dielectric bushings may include power systems, such as high-voltage feedthroughs, optical feedthroughs, etc., whereby the interaction of radiative, electrical, or other forms of energy can generate electrons in the vacuum and cause breakdown or other electronic phenomena. While the discussion herein focuses on high-voltage feedthroughs that introduce field emission electron sources into a vacuum environment, embodiments of the present disclosure may omit the conductive feedthrough and provide vacuum-tight insulating or dielectric flanges, bushings, standoffs, etc. to electrically isolate components of the vacuum system.

[0010] Advantageously, the compact components of the present disclosure represent an improvement over the current state of the art for high voltage vacuum system components. For example, the compact feedthroughs of the present disclosure are structured to introduce conductors compatible with high and low voltage operation, and are 10 -8 It is constructed to operate at sub-torr vacuum pressures and voltages of ±600 kVDC or greater with little or no stable dark current and negligible or no surface flashover (e.g., electron avalanche and ionization throughout the dielectric).

[0011] 1 is a schematic diagram of an exemplary compact feedthrough 100 configured for an operating voltage of approximately ±300 kVDC, according to an embodiment of the present disclosure. The exemplary compact feedthrough 100 includes a dielectric flange 105 and a conductor 110. The dielectric flange 105 can define a first side 115, a second side 120, and an opening 125 extending from the first side 115 to the second side 120. The conductor 110 can be disposed through the opening 125, thereby forming a contact 130 with the dielectric flange 105 at the first side 115.

[0012] In some embodiments, the dielectric flange 105 is a solid of revolution symmetric about a central axis "A." The opening 125 may be concentric with the central axis A or may be off-axis relative to the central axis A. For example, the dielectric flange 105 can be fabricated by subtractive manufacturing followed by removal of the opening 125. In some embodiments, the dielectric flange 105 can be fabricated by additive manufacturing or by multiple steps including additive and subtractive manufacturing (e.g., laser fusing of ceramic powder followed by subtractive refinement of the structure by deburring, polishing, etc.).

[0013] In some embodiments, the dielectric flange 105 is characterized by a minimum dimensionless thickness, expressed as a ratio of the width of the dielectric flange, of about 0.1 to about 2.0. As described in more detail with reference to FIGS. 3A-3C , the dielectric flange 105 may include a plurality of surface features 155 and / or recesses 160 that characterize the dielectric flange 105 with a positionally dependent local thickness. As a structure configured to withstand a relative pressure differential between the vacuum environment 145 and the ambient environment 150, the minimum dimensionless thickness 140 of the dielectric flange 105 can be determined at least in part based on the width of the dielectric flange 105, at least in part because the force acting on the dielectric flange 105 is proportional to the cross-sectional area of ​​the dielectric flange 105. In some embodiments, the minimum dimensionless thickness 140 is from about 0.1 to about 1.9, from about 0.1 to about 1.8, from about 0.1 to about 1.7, from about 0.1 to about 1.6, from about 0.1 to about 1.5, from about 0.1 to about 1.4, from about 0.1 to about 1.3, from about 0.1 to about 1.2, from about 0.1 to about 1.1, from about 0.1 to about 1.0, from about 0.1 to about 0.9, from about 0.1 to about 0.8, from about 0.1 to about 0.7, from about 0.1 to about 0.6, from about 0.1 to about 0.5, from about 0.1 to about 0.4, from about 0.1 to about 0.3, or from about 0.1 to about 0.2, including ratios and interpolations thereof. In this context, the term "about" refers to a deviation of 5% or less from the stated value. In this context, the term "minimum" does not refer to the lowest possible value (e.g., a mechanically optimized or minimized thickness determined based on physical simulations), but rather to the shortest distance between the first side 115 and the second side 120 measured across the structure of the dielectric flange 105.

[0014] The exemplary compact feedthrough 100 can be used at a given pressure (e.g., a rough vacuum above 1 torr, 1 torr to 10 -3 Medium vacuum, 10 torr -3The dielectric flange 105 may be removably attached to a vacuum chamber 165 configured to be evacuated to a pressure below torr (such as high and ultra-high vacuum). In some embodiments, the dielectric flange 105 is removably attached to the vacuum chamber 165 using a gasket (e.g., butadiene rubber, copper, ceramic, or other material) compressed between two flange faces, or between a knife edge located on the first side 115 and a knife edge of the vacuum chamber 165 located on the opposite side. In some embodiments, the dielectric flange 105 is removably attached to a metal standoff that is in turn attached to the vacuum chamber 165. In some embodiments, the dielectric flange 105 is directly integrated into the vacuum chamber 165. For example, the vacuum chamber 165 can be formed from a ceramic material, and the opening 125, features 155, and / or recess 160 can be formed in the material of the vacuum chamber 165 itself. In some embodiments, the exemplary compact feedthrough 100 forms part of a reactor system that includes a high-voltage power supply electrically coupled to the conductor 110. The high voltage power source can be electrically coupled to the conductor 110 by a resistive medium integrated into the conductor 110 or connected in series with the conductor 110. In these embodiments, the resistive medium can be a cable with a resistive core, a resistor, or the like.

[0015] In some embodiments, at least a portion of conductor 110 is housed within a secondary chamber 170 that is removably attached to second side 120 of dielectric flange 105. As described in detail with reference to the exemplary embodiment of Example 1, proximate second side 120, conductor 110 can be disposed in an oil (e.g., transformer oil) environment within secondary chamber 170. The environment can include a liquid or a gas. In an exemplary example, the environment can include SF, C3F7CN, alone or in combination with one or more gases (e.g., 30% C3F7CN / 70% CO2). Advantageously, providing a dense insulating medium in contact with conductor 110 can reduce the formation of corona discharge near second side 120, thereby improving the performance of the feedthrough at voltages above where corona discharge typically forms in air.

[0016] In some embodiments, the dielectric flange 105 comprises an insulating or dielectric material. For example, the dielectric flange 105 can be formed from or contain a vacuum-compatible solid dielectric material such as MACOR®, SHAPAL®, aluminum oxide, zirconium dioxide, aluminum nitride, boron nitride, quartz, mica, or borosilicate glass, or other vacuum-compatible solid dielectric material. In some embodiments, a coating of a non-conductive or semi-conductive material is disposed over the first side 115 of the dielectric flange 105. The coating can have a secondary electron emission coefficient lower than that of the dielectric, or preferably less than 1. In this context, the secondary electron emission coefficient refers to the number of secondary electrons emitted from the coating material in response to one electron incident on the coating's surface. A secondary electron emission coefficient less than 1 thus represents a material that is a net absorber of electrons, while a secondary electron emission coefficient greater than 1 represents a material that multiplies the number of free electrons near the first side 115. As described with reference to Example 1 below, the likelihood of surface flashover is affected by the number (e.g., density) of free electrons near the surface of first side 115. Thus, reducing the density of secondary electrons near the surface of first side 115 can reduce the likelihood of surface flashover when example feedthrough 100 is in operation.

[0017] In some embodiments, the compact feedthrough 100 can include a magnetic field to redirect electron paths away from the surface of the insulator. In this regard, the magnetic field can be applied to the electrons in a direction perpendicular to the path of at least some of the electrons traveling between the conductor 110 and the wall of the vacuum chamber 165, which wall can potentially serve as a relative anode (e.g., when a voltage is applied to the conductor 110). The magnetic field can be applied by a solenoid or other magnetic source and can be oriented along the axis of the conductor 110 such that the cross product of the electric and magnetic fields has a vector perpendicular to both the electric and magnetic fields (e.g., a magnetic source that generates a magnetic field in an upward direction relative to FIG. 1 ) to induce spiral motion of the electrons within the vacuum chamber 165. The magnetic field can be generated by any suitable magnetic source, including an electromagnetic coil, a permanent magnet, a superconducting magnet (e.g., an LK99 room-temperature superconducting magnet), or the like.

[0018] The spiral motion of electrons (e.g., whether electrons move radially outward, radially inward, or are substantially radially static during spiral motion) can be controlled by the strength of the magnetic field, and the condition of being substantially radially static is described by considering a condition called the Hull cut-off in accelerator physics. When charged particles such as protons and electrons are accelerated in a magnetic field, they follow spiral trajectories, and these particles can remain in phase with the oscillating electric field that is responsible for their acceleration. The Hull cut-off condition defines the maximum magnetic field strength at which a cyclotron can accelerate particles of a given mass-to-charge ratio. If the magnetic field is too strong (above the Hull cut-off), the particles can no longer remain in phase with the oscillating electric field, making the acceleration process inefficient.

[0019] The Hull cutoff condition for a coaxial electrode configuration can be expressed as: This equation gives the minimum magnetic field required to prevent electrons from reaching the anode.

number

[0020] 2 is a schematic diagram of an exemplary compact feedthrough 200 configured for an operating voltage of approximately ±600 kVDC in accordance with an embodiment of the present disclosure. The exemplary compact feedthrough 200 is an example of the exemplary compact feedthrough 100 of FIG. 1 , whose structure is configured to operate up to voltages of approximately ±600 kVDC or greater while exhibiting little or no stable dark current during operation and a reduced likelihood of surface flashover. Similar to the exemplary compact feedthrough 100, the exemplary compact feedthrough 200 includes a dielectric flange 105 that defines a first side 115, a second side 120, and an opening 125. The first side 115 and / or the second side 120 can define a plurality of features 155, illustrated as symmetrical concentric ridges around the opening 125. In some embodiments, the conductor 110 of the exemplary compact feedthrough 200 can be or include a purified metal configured to generate an electric field within the vacuum chamber 165 during operation (e.g., at an applied voltage of up to about ±600 kVDC). For example, the conductor 110 can be or include a conductive material characterized by a purity of about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, about 99% or higher (including ratios or interpolations thereof). The conductor 110 can be or include molybdenum, titanium, stainless steel, niobium, copper, tungsten, aluminum, nickel, tantalum, or composites and / or alloys thereof. In some embodiments, the conductor 110 can be formed from any vacuum-compatible electrode material.

[0021] In some embodiments, the dielectric flange 105 contains aluminum oxide, zirconium dioxide, aluminum nitride, MACOR, SHAPAL, boron nitride, quartz, mica, or borosilicate glass at a purity of about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, about 99%, or more (including ratios or interpolations thereof). The material of the dielectric flange 105 can be characterized by a purity above a given threshold electric field strength (e.g., greater than 15 kV / mm) such that it does not transition from dielectric to conductor. The threshold electric field strength can depend on the purity and can be adjusted, for example, by doping or by purifying the material to a higher purity.

[0022] In some embodiments, the exemplary compact feedthrough 200 is removably mounted to the vacuum chamber 165 using a dielectric standoff 176. The dielectric standoff 176 may be coated with a non-conductive or semi-conductive material characterized by a secondary electron emission coefficient less than 1. Similar to the first side 115, a net electron absorber coating can improve the performance of the electrical feedthrough by reducing the likelihood of surface flashover due to a local increase in electron density in the vacuum environment surrounding the conductor 110 near the surface of the dielectric standoff 176.

[0023] 3A-3C are schematic cross-sectional views of the compact feedthrough 100 and compact feedthrough 200 of FIGS. 1 and 2 according to embodiments of the present disclosure. The schematic views of FIGS. 3A-3D illustrate example cross-sectional views intended to highlight the structural elements of the dielectric flange 105 and the conductor 110, from which various improvements and functions of the example compact feedthrough 100 and example compact feedthrough 200 are derived, as described in more detail with reference to FIGS. 1 and 2. For example, FIG. 3A illustrates a portion of the cross-section of the example compact feedthrough 100 of FIG. 1, focusing on the triple junction (TJP) between the first side 115 of the dielectric flange 105 and the conductor 110. FIGS. 3B and 3C illustrate a region of the first side 115 that includes multiple features 155, the structure of which is configured to attenuate electron flow between the conductor 110 and the vacuum chamber 165. FIG. 3D shows the corresponding region of the example compact feedthrough 200 of FIG. 2, including the conductor 110 and the first side 115 of the dielectric flange 105.

[0024] As described in more detail with reference to FIG. 3 , conductor 110 can be or include a body of revolution having a cross-section that is rotationally symmetric about an axis of rotation and defined in part by a compound curve 305. Compound curve 305 can include a first curve segment 310 having a first radius of curvature. Compound curve 305 can also include a second curve segment 315 having a second radius of curvature that is greater than the first radius of curvature of first curve segment 310. In some embodiments, the second radius of curvature is also equal to or less than about 20 mm, about 19 mm, about 17 mm, about 16 mm, about 15 mm, about 14 mm, about 13 mm, about 12 mm, about 10 mm, about 9 mm, about 8 mm, about 7 mm, about 6 mm, or about 5 mm, including ratios and interpolations thereof. In further embodiments, the first radius of curvature of first curve segment 310 is equal to the second radius of curvature of second curve segment 315.

[0025] As shown, the first curved segment 310 may be closer to the first side 115 and the second curved segment 315 may be farther from the first side 115. In some embodiments, the compound curve 305 includes a third segment 320, with the first curved segment 310 located between the third segment 320 and the second curved segment 315. The third segment 320 may be shaped to receive the dielectric flange 105 at the first side 115 and form a contact between the first side 115 and the third segment 320. In some embodiments, the third segment 320 and / or the first side 115 include a knife edge 325. Knife edge 325 can facilitate the formation of a vacuum-tight seal at the contact, for example, by compression of gasket 175 (e.g., a ring formed from copper, aluminum, flexible graphite, stainless steel, cast steel, Monel, Inconel, brass, bronze, or any combination thereof) between first side 115 and third segment 320. In some embodiments, the contact between first side 115 and conductor 110 can be formed by metallizing dielectric flange 105 in the contact area and vacuum brazing the two components to form a hermetic seal.

[0026] As described in more detail with reference to Example 1 below, the structure of the conductor 110 and the dielectric flange 105 can provide functional improvements to the exemplary compact feedthrough 100 and exemplary compact feedthrough 200 described herein. For example, the size and curvature of the compound curve 305 can reduce the likelihood of surface flashover, as well as the stable dark current exhibited during high-voltage operation. Therefore, locations with high aspect ratios or surface irregularities, such as imperfections in surface polishing or machining artifacts, can cause localized electric field concentrations and increased emission current from “hot spots” on the surface of the conductor 110. Thus, the first radius of curvature of the first curve segment 310 can configure the TJP such that the contact between the dielectric flange 105 and the conductor 110 is shielded by the first curve segment 310 from the features 155 on the first side 115, thereby reducing the localized electric field around the TJP and reducing the electron emission current from the TJP. Because TJPs are typically points of electric field concentration, shielding or otherwise reducing the electric field strength in the area surrounding the TJP can reduce the likelihood of surface flashover at high electric field strengths.

[0027] In some embodiments, the first radius of curvature can be from about 0.5 mm to about 10 mm. If the first radius of curvature is less than about 0.5 mm, the composite curve 305 can concentrate the electric field at the apex of the first curve segment 310, thereby increasing the likelihood of field emission of electrons from the conductor and increasing the electron density near the surface of the first side 115. For example, above 8 mm, the composite curve 305 can approach a distance from the vacuum chamber 165 that allows electrons to traverse that distance (such as by tunneling), thereby increasing the stable dark current.

[0028] In some embodiments, the first curved segment 310 meets the third segment 320 at an angle “α.” The angle α can be from about 15 degrees to about 345 degrees relative to a radial axis B of the dielectric flange 105, which is perpendicular to the rotation axis A. The value of the angle α affects the degree of shielding of the electric field at the TJP from the first side 115, with an angle α of about 90 degrees corresponding to a line tangent to the first curved segment 310 being parallel to the rotation axis A. Similarly, an angle α of about 0 degrees or about 180 degrees corresponds to a line tangent to the first curved segment 310 being parallel to the radial axis B.

[0029] A cross-section of first side 115 can define a first segment 330 substantially perpendicular to rotation axis A. The cross-section can also define an annular recess 335 concentric with opening 125. Annular recess 335 can be continuous with first segment 330. Annular recess 335 can be defined by an inner portion 340 having a semicircular cross-section with a radius "R." With respect to radius R, in some embodiments, the first radius of curvature can be from about 0.5 mm to about ½R mm.

[0030] The cross section can define a first feature 155-1 that is contiguous with the annular recess 335. The first feature 155-1 can include an inner surface 345 and an outer surface 350. The inner surface 345 can be located closer to the axis of rotation A than the outer surface 350. The inner surface 345 can be separated from the conductor 110 by a non-dimensional distance 355, defined as the ratio of the dimensioned distance between the compound curve 305 and the inner surface 345 to the overall radius of the dielectric flange 105, ranging from about 0.1 to about 1.0. Advantageously, defining the non-dimensional distance 355 relative to the overall dimensions of the dielectric flange 105 allows the annular recess 335 to be defined at least in part based on the overall dimensions of the dielectric flange 105 rather than a predetermined geometric shape. In this manner, the example compact feedthrough 100 and the example compact feedthrough 200 can be scaled relative to a single geometric dimension rather than a physical simulation. Additionally, electron phenomena may be due to the structural configuration of the electrode and the inner surface of first side 115, and simulations may determine a distance below which surface flashover is more likely to occur. In contrast, a dimensionless distance 355 above a given value may allow electrons emitted from conductor 110 to accelerate in the electric field emanating from conductor 110 and reach velocities that make the electrons more likely to generate secondary electron re-emission and increase the likelihood of surface flashover. Because acceleration depends on the strength of the electric field, different operating parameters will have different effects on the simulation of electron behavior. To that end, the dimensionless distance 355 can be from about 0.01 to about 1.0, from about 0.1 to about 1.0, from about 0.2 to about 1.0, from about 0.3 to about 1.0, from about 0.3 to about 0.9, from about 0.3 to about 0.8, from about 0.3 to about 0.7, from about 0.3 to about 0.6, from about 0.3 to about 0.5, from about 0.3 to about 0.4 (including ratios and interpolations thereof).

[0031] As shown in FIGS. 1 and 3B and 3C, the dielectric flange 105 can include multiple features 155 of different sizes, shapes, and orientations. Illustrated is a portion of a cross section of the dielectric flange 105 according to an embodiment of the present disclosure. The cross section includes a first feature 155-1, a second feature 155-2, and a third feature 155-3. In FIG. 3B, the first feature 155-1 defines an inner surface 345 and an outer surface 350. In FIG. 3C, the first feature 155-1 defines an inner surface 345 and an outer surface 350 and further defines a lateral protrusion 351 and an electron confinement zone 352. The second feature 155-2 defines a second inner surface 360 ​​and a second outer surface 365. The third feature 155-3 similarly defines an inner surface and an outer surface. In some embodiments, the third feature 155-3 is located farther from the axis of rotation A than the first feature 155-1.

[0032] Although the features 155 in FIGS. 1-3D are generally depicted as concentric ridges having rounded or sharp triangular cross-sections, it is contemplated that the features 155 may be shaped differently. For example, FIG. 3C shows a first feature 155-1 having a lateral protrusion 351 and an electron confinement zone 352. The electron confinement zone 352 of the first feature 155-1 is oriented at least partially in the direction of the electric field. This orientation forces electrons moving along the electron confinement zone 352 to move in a direction opposite the electrostatic force (e.g., moving against the electric field), which is practically impossible, trapping the electrons along the surface 352. In further embodiments, the features 155 may be shaped as concentric ridges having rounded rectangular cross-sections, polygonal cross-sections, curvilinear cross-sections (e.g., compound curves, scimitar curves, etc.), etc. In an illustrative example, feature 155 can include one or more raised or protruding surfaces, such as concentric ridges including an inner stem and an outer base, where a first region of feature 155 located closer to radial axis B is narrower than a second region of feature 155 located farther from radial axis B.

[0033] The first feature 155-1 can be characterized by a first height 375, and the second feature 155-2 can be characterized by a second height 370. In some embodiments, the second height 370 is smaller than the first height 375. In some embodiments, the second height 370 is larger than the first height 375. The third feature 155-3 can be characterized by a third height 380, which can be different from the first height 375 and the second height 370. In some embodiments, each feature 155 included as part of the first side 115 can be characterized by a different height, which can be a random height within a range of heights that enables the features 155 to interrupt the trajectory of electrons between the conductor 110 and the vacuum chamber 165. The features 155 can be divided into two or more groups by height. For example, a first subset of the features 155 can be characterized by a first height 375, and a second subset of the features 155 can be characterized by a second height 370. In some embodiments, the height of a given feature 155 is proportional to the radial distance of the given feature 155 from the axis of rotation A. For example, the difference between the first height 375 and the third height 380 can define a non-zero angle “γ” with respect to the radial axis B of the dielectric flange 105. In some embodiments, the angle γ can range from −75 degrees to 75 degrees. In an illustrative example, the dielectric flange 105 can further include a fourth feature 155-4 located farther from the axis of rotation A than the third feature 155-3, and the fourth feature 155-4 is characterized by a height defined by the angle γ with respect to the first height 375 and the third height 380. Advantageously, gradually increasing the height of the feature with increasing distance from axis A reduces the effect of field acceleration of electrons between conductor 110 and vacuum chamber 165 by disrupting the straight line trajectory between vacuum chamber 165, which may potentially be a relative anode (e.g., when conductor 110 is energized), and composite curve 305 and / or TJP.

[0034] To that end, one or more angles “β” can be defined by the interior surface of the feature 155. The angle β can improve the performance of the dielectric flange 105 in at least partially reducing the likelihood of surface flashover, in that an angle of the interior surface providing near-normal incidence can reduce secondary electron re-emission, for example, by moving the interaction volume deeper into the dielectric material. In contrast, a smaller angle of incidence moves the electron interaction volume closer to the interior surface 345, increasing the likelihood that secondary electrons will escape the dielectric material. Thus, a smaller value of β, closer to alignment with the rotation axis A, is generally more effective at absorbing incident field-emitted electrons from the conductor 110. However, in some cases, the angle β can be greater than zero for multiple reasons. For example, the relative orientation of the composite curve 305 and the first feature 155-1 provides a likely trajectory for emitted electrons that is not aligned with the radiation axis B. Similarly, manufacturing methods may limit the value of the angle β to a non-zero value. In some embodiments, inner surface 345, inner surface 360, and / or other inner surfaces of feature 155 can be oriented at an angle β relative to axis of rotation A between about 0 degrees and about 90 degrees, between about 0 degrees and about 75 degrees, between about 0 degrees and about 60 degrees, between about 0 degrees and about 45 degrees, between about 0 degrees and about 30 degrees, between about 0 degrees and about 15 degrees, between about 0 degrees and about 10 degrees, or between about 0 degrees and about 5 degrees (including ratios and interpolations thereof).

[0035] As distinguished from first height 375, second height 370, and third height 380, features 155-1, 155-2, and 155-3 can be characterized by respective inner and outer lengths corresponding to the surfaces of each feature 155. In this manner, the overall shape of feature 155 can be described by the radial surface lengths of the inner and outer surfaces, which resemble the path electrons travel along the surface of dielectric flange 105. In an example of a substantially triangular cross-section of concentric raised features (e.g., a substantially triangular shape due to the rounded junction of the inner and outer surfaces), the ratio of the lengths of each feature can define the height or angle β. As a dimensionless parameter, the ratio of the inner length to the outer length can be used to scale features 155 for various sizes of exemplary feedthrough 100 and exemplary feedthrough 200.

[0036] In some embodiments, the ratio of the length of the first inner surface 345 to the first outer surface 350 is about 0.01 to about 3.0. From a geometric perspective, having the inner surface of the feature 155 shorter than the outer surface provides a smaller β value, based at least in part on manufacturing constraints regarding the relative orientation of the inner and outer surfaces. Thus, a smaller ratio improves electron absorption. However, it also introduces a balance between the number of features 155 and the height of the features 155. At greater heights, the ratio limits the number of features, while at the same time, a greater number of features reduces the available space for each feature, limiting the height. Thus, the ratio of the length of the first inner surface 345 to the first outer surface 350 can be about 0.01 to about 2.5, about 0.01 to about 2.0, about 0.01 to about 1.5, about 0.01 to about 1.0, about 0.01 to about 0.5, about 0.01 to about 0.1, and the like (including ratios and interpolations therein).

[0037] FIG. 3D illustrates an exemplary cross section of the dielectric flange 105 and conductor forming a triple junction as part of the exemplary feedthrough 200 of FIG. 2. This exemplary cross section omits the features of the exemplary feedthrough 200 to better illustrate the configuration of the recess 385 and concentric features 155 that together form the exemplary feedthrough 200, operating at voltages above −600 kVDC and up to +600 kVDC with little or no potential for surface flashover and reduced or no stable dark current. As illustrated, the angle γ can be larger than the value illustrated for the relatively low voltage configuration of the exemplary feedthrough 100 of FIG. 1. Advantageously, the larger angle increases the angular sweep between the conductor 110 and the vacuum chamber 165 that is intercepted by the features 155, thereby further reducing the number of electrons that can travel from the conductor 110 to the vacuum chamber 165 without striking the features 155. Similarly, angle β is shown to be non-zero, but relatively smaller than the value illustrated in FIGS. 3A-3C. Similar to angle γ, the facing angle of the interior surfaces of feature 155 may be reduced to account for a higher average linear velocity of electrons, due at least in part to a stronger electric field generated by a higher applied voltage. Increasing electron velocity increases the likelihood of secondary and / or backscattered electron generation, and the average energy of the secondary / backscattered electrons may be higher, making the shape of the interaction volume within feature 155 important. Thus, increasing the applied voltage may reduce the value of β. Similarly, increasing the applied voltage may increase the likelihood of secondary discharge formation (e.g., corona discharge) on second side 120 of dielectric flange 105. Thus, conductor 110 may incorporate one or more recesses 385 that provide a gap between conductor 110 and a central element 390 to which a power coupling may be removably attached.

[0038] Example 1: Compact 300kVDC bushing for operation under ultra-high vacuum pressure

[0039] The following is a description of exemplary embodiments of the feedthrough of the present disclosure. The simulation results, schematics, and operating windows are intended to illustrate non-limiting examples of feedthroughs configured to operate under high and low voltages while reducing dark current. Embodiments of the present disclosure include additional and / or alternative components, features, or operating parameters other than those described below.

[0040] introduction

[0041] Increasing energy demand and global climate change require an increased proportion of sustainable energy sources. Fusion energy has the potential to provide a zero-carbon, low-waste energy source that could revolutionize the energy industry. As a fusion fuel, one gram of hydrogen isotope is 16m 3 It is possible to provide an energy equivalent to the combustion of 10 ... -8 The delivery of high voltages to vacuum chambers (up to 1000 kV) introduces challenges such as ionization / breakdown of gas atoms or molecules in the vacuum and surface flashover across surfaces near the feedthroughs used to pass current into the vacuum chamber. The exemplary embodiment described herein achieves a current of approximately 100 nA / mm at an applied voltage of approximately ±300 kV. 2 The compact bushing is configured to conduct current to the vacuum chamber at a dark current of:

[0042] Currently, oil and other fossil fuels are experiencing record prices and unprecedented volatility. This is occurring at a time when the world desperately needs to address rising CO2 levels. Global CO2 emission levels have increased by 90% since 1970, with fossil fuels accounting for 78% of carbon emissions. In the United States, renewable energy consumption has nearly quadrupled since 1950. As of 2020, renewable energy represents 12% of total U.S. energy generation. According to the U.S. Energy Information Administration (EIA), renewable energy production is expected to exceed 20 EJ in 2050, which is less than 20% of projected total energy consumption.

[0043] Research into generating energy through nuclear fusion power began in earnest in 1938. In a fusion reaction, light elements (such as hydrogen) are excited to the point where their nuclei can fuse. The output of this reaction is relatively heavy atomic nuclei and energy. Several methods for generating fusion power have been proposed, but all have failed to operate with a net positive energy output (e.g., a positive Q factor). Thermonuclear fusion technology involves a tokamak configuration, in which a hot plasma confined by a strong external magnetic field is contained within a torus. The International Thermonuclear Experimental Reactor (ITER), based in France, is an example. The goal of the ITER collaboration is to prove that net positive fusion power is technically feasible. It is estimated that an input power of 50 MW can produce 500 MW of power for 6 to 10 minutes. The seven-party collaboration is estimated to cost at least $22 billion.

[0044] There are at least a dozen government and private companies targeting technologies in tokamak, inertial confinement fusion, magnetized target fusion, field-reversed configurations, and stellarator configurations. An embodiment of the present disclosure is directed to a system for confining fast ions, known as the "Orbitron," which includes relatively small magnets and does not use lasers to provide energy for fusion (as in Z-pinch devices). Unlike other fusion configurations, the Orbitron device is configured with a smaller footprint and generates over 5 kW of power, which can be used to power electric vehicles, aircraft, and local or regional power grids. In an Orbitron device, ions are co-confined by an electrostatic field and a relatively weak magnetic field perpendicular to the electrostatic field. In an embodiment of the present disclosure, the plasma volume is relatively small and is maintained by an electric field generated by an applied voltage on the order of ±100 kV.

[0045] Exemplary embodiments described herein describe a feedthrough configured to support applied voltages on the order of ±100 kV without dielectric breakdown for generating electric fields in a vacuum environment as part of the generation of fusion plasma in an Orbitron configuration. In some embodiments, the compact bushing can be mounted at pressures on the order of ±100 kV from atmospheric pressure. -8 The configuration described herein is configured to transmit ±300 kV DC down to below torr. Advantageously, the configuration described herein reduces surface flashover across the dielectric in a vacuum and provides a 220 in. 3 Validation of the configuration described here was performed by electrostatic simulation of electrical stresses and particle trajectories to assess the risk of surface flashover.

[0046] Design Considerations

[0047] The disclosed feedthrough bushings are configured to transmit high voltages from a high-pressure ambient environment to a low-pressure vacuum environment, thus enabling a system to sustain a fusion plasma while addressing several constraints and technical challenges posed by difficult operating conditions, including dielectric breakdown, vacuum arc formation, surface flashover, and elevated and stable dark currents.

[0048] The feedthroughs of the present disclosure may include a conductor material and a dielectric or insulating material. The dielectric strength of the insulator material may determine the thickness of the insulator used to avoid dielectric breakdown. Under operating conditions (p<1×10 -8 Due to the high vacuum pressure (torr), the materials used for the bushing include ultra-high vacuum compatibility (e.g., structural and material properties such as low outgassing). Most plastic insulators, such as polyvinyl chloride (PVC), polyetheretherketone (PEEK), and polyethylene (PE), are characterized by relatively high levels of outgassing and are therefore unsuitable for operation in ultra-high vacuum. Ceramics, such as aluminum oxide, SHAPAL, and MACOR, are characterized by relatively low outgassing rates and relatively high dielectric strength. In this exemplary embodiment, the feedthrough includes MACOR for a system operating under a field strength of approximately 129 MV / m.

[0049] For DC systems, discharge breakdown in a vacuum can be modeled using Paschen's law, which relates dimensions such as electrode gap distance to operating conditions such as vacuum pressure and applied voltage. -8 At pressures of 1000 torr, the mean free path of electrons is approximately λ ≥ 5000 m. As a result, it is unlikely that free electrons will participate in an electron avalanche as part of the discharge spark.

[0050] At chamber and component surfaces exposed to electric fields, secondary electron emission can induce surface flashover (e.g., across the insulator surface), which may involve dark current or sparking of volume discharge within the volume. Surface flashover is influenced by the surface conditions of the dielectric and electrode components of the feedthrough bushing. Surface flashover can proceed by a three-step mechanism, including (1) field emission of electrons from the electrode (e.g., at the triple junction), (2) secondary electron emission avalanche across the surface of the dielectric, and (3) Townsend ionization of desorbed gases from the surface of the dielectric.

[0051] Dark current refers to the electron flux from the electrode that is not accompanied by a discharge spark, such as field emission of electrons into the vacuum. Dark current can be a function of the geometry, material, and cathode surface area. Dark current is related to the first step of the surface flashover mechanism described above. Dark current drawn from the power supply can limit the power supply's output voltage, increasing the vacuum system's power demand to generate the same field strength within the vacuum. Higher current also increases the voltage drop across the power supply's current-limiting resistors. Thus, the applied voltage can be significantly lower than the power supply's output voltage.

[0052] The compact feedthrough design of an exemplary embodiment is shown in Figure 1. The feedthrough measures 6" x 6" x 6". As a result, the electric field strength can be significant at the surface of the cathode. To reduce the possibility of flashover, the cathode and dielectric flange, along with the ratio of the cathode to anode diameters, are configured to keep the electric field strength below the flashover threshold at approximately ±300 VDC.

[0053] The dielectric flange acts as a spacer between the two media: vacuum and oil at atmospheric pressure. The choice of oil as the insulating medium improves the electrical stability of the cable-cathode junction. The sawtooth design of the uneven wedges on the surface of the insulator traps potential electrons that may attack the surface of the insulator.

[0054] As shown in Figure 1, the cathode is not completely cylindrical, but consists of a hemispherical section on the vacuum side and a truncated conical section on the oil side. The hemispherical portion of the cathode localizes the triple junction (TJP) within the equipotential well, minimizing electric field tension. The truncated cone is internally threaded, which helps seal the cathode-insulator interface at a 45-degree angle with the dielectric flange.

[0055] The anode was geometrically configured in terms of gap distance as an approach to increasing the breakdown voltage within the gap above the cathode's operating voltage to reduce electron generation due to field emission. The cathode and anode were made of molybdenum and stainless steel, respectively. To reduce particle emission, both surfaces were polished to reduce the presence of surface irregularities. The feedthrough was tested for breakdown and dark current measurements using a 300 kVDC power supply with a 15 MΩ current-limiting resistor. Measurements were performed using a high-sampling-rate ammeter.

[0056] Electrostatic simulations were completed to assess the strength of the mechanical stresses on the feedthrough during operation under vacuum. Additionally, particle trajectory analysis was integrated with the electrostatic simulations to assess the likelihood of surface flashover. Figures 4 and 5 show the electric field and potential distributions, respectively, at the center cut of the bushing. The results presented in Figures 4 and 5 correspond to a voltage of -300 VDC applied to the cathode and the anode grounded.

[0057] The conductor and dielectric flanges are structured to reduce and / or minimize the electric field intensity at the triple junction (TJP). Figure 4 shows that the electric field maximum in the exemplary geometry does not occur at the TJP. Instead, the electric field is maintained below 20 MV / m at the TJP due to the creation of an equipotential well around the TJP. In this way, the electric field intensity at the TJP does not cause significant electron emission, reducing the possibility of electron flux-induced flashover. For vacuum breakdown, the breakdown voltage of the linear approximation of Paschen's law is >10 for a gap distance of 3.5 cm in air. 10 This gives a breakdown voltage of 100 MV. The electric field is estimated to be greatest at approximately 41.7 MV / m at the outer surface of the corresponding cathode opposite the TJP. As a result of the dielectric flange construction, electrons emitted from the outer surface of the cathode cannot reach the anode, further reducing the likelihood of surface flashover.

[0058] Particle trajectory analysis

[0059] To evaluate the possibility of flashover in feedthroughs, particle trajectories were simulated for extreme cases of electron emission from the cathode surface. The simulation evaluated the trajectories of secondary electrons emitted from the surface of an insulator. The number of electrons emitted from the cathode surface is controlled by the field emission mechanism, and the electron emission rate follows the Fowler-Nordheim equation:

number

[0060] From equation (1), we can see that the macroscopic electric field distribution due to voltage level and gap distance has less effect on the electron emission rate than the local microscopic field enhancement factor β, which is highly dependent on the surface treatment and conditioning approach. The dependence of β on the microscopic surface conditions makes it difficult to predict the level of field emission without experimentation.

[0061] The rate of electron field emission from the cathode surface can be inferred from the magnitude of the steady current drawn from the HV power supply, known as the dark current. Preliminary measurements of dark current were completed for four metals (NK Clean Z stainless steel, 99.996% Class 1 OHFC copper, JIS Grade 2 pure titanium, and 99.999% molybdenum) at different field strengths. For stainless steel and copper, dark currents exceeded 1 nA at field strengths of approximately 40–50 MV / m. In contrast, for titanium and molybdenum, dark currents exceeded 1 nA at field strengths greater than 100 MV / m. At field strengths below 75 MV / m, the dark current for titanium and molybdenum was nearly zero. Therefore, molybdenum was selected as the cathode to operate as a +300 kVDC feedthrough, and the gap distance was determined to reduce the maximum field strength to less than 75 MV / m (e.g., 3.5 cm or greater).

[0062] In the electron trajectory simulation, an electron source is located on the surface of the cathode and emits electrons at a rate proportional to the current given by the Fowler-Nordheim equation (Eq. (1)). The initial kinetic energy of the electrons was assumed to be 300 keV (the energy due to the highest applied voltage), and their initial direction was aligned with the electric field direction. While the secondary electron emission efficiency (SEEY) of MACOR can be as high as 1.5, the scope of the study is limited to relatively low-energy incident particles. To simulate the worst-case scenario, an SEEY of 2 was considered, corresponding to a secondary electron re-emission event activated by each electron impacting the dielectric surface. The initial velocity of the secondary electrons was considered to be dominated by diffuse scattering, and the secondary electron velocity was assumed to be the same as the incident electron velocity. This extreme scenario is far from the actual secondary electron efficiency. Nevertheless, considering an SEEY of 2 provided a feedthrough structure configured to operate reliably with no flashover and limited dark current.

[0063] Figure 6 shows the simulated trajectories of emitted and secondary electrons. The emission sites of electrons emitted from the cathode surface are visible. It can also be observed that the majority of electrons emitted from the cathode impinge on the anode without causing secondary electron re-emission across the dielectric surface. The second stage of surface flashover causes electron avalanches across the dielectric surface. This occurs when electrons emitted from the cathode impinge on the dielectric surface, and secondary electrons re-emitted from the dielectric surface increase the number of electrons traveling toward the anode. Figure 7 shows a detailed view of the vacuum-side surface of the dielectric flange, including secondary electron trajectories. As shown, the simulation results indicate that many, most, or all of the field-emitted electrons impinging on the insulator surface are suppressed by the first wedge of the dielectric sawtooth design. Furthermore, the secondary electron trajectories passing through the first wedge are such that the likelihood of secondary electron generation is sufficiently low that an electron avalanche is unlikely or impossible.

[0064] conclusion

[0065] High voltage electron sources form a vital component of electrostatic confinement based fusion reactors. The compact feedthrough bushing of the present exemplary embodiment has a p<10 -8 The insulator is configured to operate at approximately +300 kVDC below torr with no surface flashover and little to no dark current. The cathode material selection reduces dark current and allows for relatively high field strengths. Localizing the triple junction describing the contact between the conductive cathode, the dielectric flange, and the vacuum within the equipotential well has shown improved performance in terms of maintaining the rate of electron emission below the rate at which surface flashover would likely occur. The insulator structure, which includes multiple sawtooth wedge mechanisms, is configured to operate in extreme conditions of secondary electron emission, with less than 5% of field-emitted electrons striking the insulator surface in a vacuum, with nearly all field-emitted electrons being deflected by the first wedge of the sawtooth design.

[0066] In the foregoing description, specific details are set forth to provide a thorough understanding of exemplary embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the presently disclosed embodiments may be practiced without all of the specific details. In some instances, well-known process steps have not been described in detail in order to avoid unnecessarily obscuring various aspects of the present disclosure. Furthermore, it will be understood that embodiments of the present disclosure may employ any combination of the features described herein.

[0067] This application may refer to quantities and values. Unless specifically stated otherwise, such quantities and values ​​are not intended to be limiting, but rather exemplary of possible quantities or values ​​relevant to this application. In this regard, this application may also use the term "plurality" to refer to a quantity or value. In this regard, the term "plurality" is intended to mean any number greater than 1, e.g., 2, 3, 4, 5, etc. Terms such as "about," "approximately," and "near" mean plus or minus 10% of the stated value. For purposes of this disclosure, the phrase "at least one of A and B" is equivalent to "A and / or B," or vice versa, i.e., "A" alone, "B" alone, or "A and B." Similarly, for example, the phrase "at least one of A, B, and C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), and if more than three elements are listed, further includes all possible permutations.

[0068] It should be noted that for purposes of this disclosure, terms such as "upper," "lower," "vertical," "horizontal," "forward," "rearward," "inner," "outer," "front," "rear," and the like are to be construed as descriptive and not limiting the scope of the claimed subject matter. Furthermore, the use herein of "including," "comprising," or "having," and variations thereof, is meant to encompass the subsequently listed items and their equivalents, as well as additional items. Unless otherwise limited, the terms "connected," "coupled," and "mounted," and variations thereof, herein are used broadly and encompass both direct and indirect connections, couplings, and mounting.

[0069] Throughout this specification, technical terms may be used, and these terms shall have their ordinary meaning within the technical field to which they are derived unless specifically defined herein or unless a different meaning is clearly indicated by the context of their use.

[0070] The principles, exemplary embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, the aspects of the present disclosure that are intended to be protected should not be construed as limited to the particular embodiments disclosed. Moreover, the embodiments described herein are to be considered illustrative rather than restrictive. It will be understood that variations and modifications may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, all such variations, modifications, and equivalents are expressly intended to be included within the spirit and scope of the present disclosure as claimed.

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