High-frequency coaxial cable for electric propulsion

Abstract

This RF coaxial cable offers low power loss at high frequencies, high radial heat dissipation, and advanced flexibility / bending rigidity. [Solution] A high-frequency (RF) coaxial cable 10 used in situations requiring high AC transmission at high frequencies, comprising: a single hollow inner conductor 101 having a flexible metal shield 101a and a hollow forming body 101b; an insulator 102 on the hollow inner conductor 101; an outer conductor 103 formed from a second flexible metal shield on the insulator 102; an outer sleeve 104 on the outer conductor 103; and an electromagnetic compatibility (EMC) overbraid 105 on the outer sleeve 104.

Description

[[TECHNICAL FIELD]]

[0001] The present disclosure generally relates to radio frequency (RF) feeding coaxial cables for electric propulsion used in situations requiring high-frequency large alternating current (AC) transmission. In particular, the present disclosure relates to an loss-optimized RF feeding coaxial cable for electric propulsion, which is used in severe and complex situations involving factors such as cable bending, radiation, and temperature, for example, for RF ion thrusters, preferably grid-type ion thrusters. [[BACKGROUND ART]]

[0002] Fig. 1 shows a system 1 such as a satellite, comprising a coaxial cable 10 and a coaxial cable 10pa connecting an RF AC power source 30 and a radio frequency ion thruster (RIT) 20.

[0003] The RF current source 30 may be, for example, an inverter that converts direct current (DC) from a corresponding satellite bus into high-frequency / RF alternating current, for example, an RF generator (RFG). The RIT 20 may be a thruster for translational propulsion / acceleration of the satellite along any axis in a three-dimensional coordinate system, and / or a thruster for rotational propulsion / acceleration of the satellite around any axis (yaw, pitch and / or roll) in the three-dimensional coordinate system. Additionally or alternatively, the RIT 20 may generate and accelerate plasma via a grid-type system.

[0004] Fig. 2A shows a coaxial cable 10pa according to the prior art.

[0005] For the RIT 20 to operate, high current at high frequency must be transmitted. In the prior art, as shown in Fig. 2A, a coaxial cable 10pa is generally used for this purpose, which comprises an outgoing / inner conductor 101pa in the core, and a return / outer conductor 103pa concentrically arranged with an insulating material / insulator 102pa sandwiched therebetween. The coaxial cable 10pa may further comprise an outer sleeve 104pa.

[0006] As mentioned earlier, AC transmission at high frequencies suffers significant losses because the effects occurring within this operating range drastically reduce the effective cross-sectional area of ​​the electrical conductor that is effectively utilized by AC. This effect is primarily manifested by the fact that the flowing current is "shifted" toward the edge layer of the conductor (the so-called skin effect). Conventional coaxial cables 10pa for RF applications often use so-called Litz cables (or stranded cables) as conductor bundles / strands 101pa-str (of which three are, for example, linked to the sign) within the core to minimize losses. These strands 101pa-str have a relatively small diameter d s It can have this, which means that the aforementioned effect is not very pronounced.

[0007] However, a disadvantage is that a large number of stranded wires 101pa-str are required to transmit a suitable current. The advantage of a low severity of the skin effect in a densely packed bundle is partially offset by the immediate displacement effect (so-called proximity effect) that occurs between stranded wires 101pa-str with the same potential. Due to the large number of stranded wires 101pa-str, such a cable 10pa also has high bending stiffness, meaning it is not always suitable for use in applications such as swivel thrusters.

[0008] Figure 2B is a graph for a conventional RF coaxial cable 10pa, where the temperature gradient of the cable core / shell is plotted on the vertical axis against the overall outer diameter of the coaxial cable 10pa on the horizontal axis.

[0009] As shown in Figures 2A and 2B, another disadvantage of conventional RF coaxial cable 10pa is the effect of its small overall diameter d0 (horizontal coordinate in Figure 2B, see also Figure 2A) on the temperature / temperature gradient (vertical coordinate in Figure 2B) that occurs during operation. Two sample values, one with a cable core diameter of 14.6 mm (labeled "conventional product") and the other with a cable core diameter of 19.1 mm, are shown by dashed lines. The first value represents an RF coaxial cable currently used in thrusters, with a core diameter of 3.37 mm and a core / shell temperature gradient of 90 K, which reaches temperatures exceeding the material limit. On the other hand, the second value represents an ideal case (which is idealized because capacitance also increases in reality), illustrating the advantage of increasing the core diameter (i.e., 7.87 mm compared to 3.37 mm above) while maintaining all other material thicknesses, thereby reducing the core / shell temperature gradient from 90 K to 50 K.

[0010] On the one hand, reducing the diameter is necessary to ensure the mechanical flexibility of cable 10pa. However, on the other hand, this constraint means that the resulting small diameter of the inner conductor will result in an extremely small contact surface with the adjacent layer (insulating material / insulator 102pa). As a result, the heat generated in the output conductor 101pa TIFF2026145038000002.tif813 can only dissipate to a limited extent to the outside, and as a result, "heat accumulation" occurs within the cable core 101pa, resulting in a high temperature gradient (see vertical axis in Figure 2B), and therefore, core 101pa( TIFF2026145038000003.tif813) and cable 10pa( TIFF2026145038000004.tif913) Surface / Outer Sleeve 104pa There is a risk of insufficient heat transfer during the TIFF2026145038000005.tif1013) process. [Overview of the project] [Problems that the invention aims to solve]

[0011] Thus, there is a need to realize improved coaxial cables suitable for situations requiring high AC transmission at high frequencies, such as RF ion thrusters, preferably grid-type ion thrusters.

[0012] These objectives are addressed by the present invention as defined by the independent clauses. Preferred embodiments are defined by the dependent clauses.

[0013] This disclosure can be summarized as follows without losing its universality:

[0014] The cable disclosed in this invention employs an alternative approach to existing cables, combining the required reduction of losses during transmission with a high degree of mechanical flexibility, and achieving a significantly reduced temperature gradient between the forward conductor in the core and the cable surface.

[0015] For this purpose, a specific geometric structure and a suitable combination of materials are used. Instead of a forward conductor consisting of bundles of multiple strands, as in conventional RF cables, a single waveguide / hollow conductor is used, similar to those commonly found in the less relevant field of fixed conductors, such as the tubular shapes in antenna technology. This has the advantage of avoiding design losses due to proximity effects between adjacent conductors at the same potential, compared to stranded wires. Hollow conductors also offer the advantage of being able to be optimally designed for current distribution caused by the skin effect (high current density in the edge layer). This maximizes the use of available conductor cross-sectional area and minimizes the amount of conductor material that is unnecessary because current does not flow through it. However, the hollow conductor tubes used are not suitable for this purpose due to their lack of flexibility, so a flexible metal shield is used in this case. To hold this shield in place within the structure, it is mounted on a plastic molded body. This molded body is hollow to minimize the bending stiffness of the structure. The return conductor in this design is also designed as a shield, as is customary in coaxial cables.

[0016] Another disadvantage of conventional RF cables is the often-overwhelming effect of their small overall diameter on the temperature generated during operation. Reducing the diameter is necessary to ensure the cable's mechanical flexibility. However, this constraint simultaneously means that the resulting small diameter of the inner conductor leads to an extremely small contact surface with the adjacent layer (insulating material). Consequently, heat generated within the output conductor can only be dissipated to a limited extent, resulting in "heat accumulation" within the cable core and a high temperature gradient between the core and the cable surface. Therefore, the core of the described new cable lies in the selected diameter of the inner conductor shield. This diameter is designed to be a compromise / optimal balance between low power loss, good / high radial heat dissipation, and low capacitance per unit length. The latter is essential for specific applications in the resonant circuits of RIT thrusters.

[0017] In addition, this disclosure enables the following advantages:

[0018] This enables the selection of suitable insulating materials between the forward and return conductors, which have low mechanical rigidity and good electrical properties, and allows for optimized cable design using a combination of hollow core / hollow conductor (e.g., held by a plastic molded body).

[0019] This allows for an increase in the diameter of the forward conductor compared to conventional cables, without significantly increasing bending rigidity.

[0020] By using a metal shield as a hollow conductor, the effective cross-sectional area of ​​the conductor that is effectively utilized by AC is maximized.

[0021] This significantly improves heat dissipation from the cable core to the outside.

[0022] Reducing losses and temperature, along with enabling the high degree of flexibility / bending rigidity required in RF cables, is a fundamental prerequisite for the successful operation of such RF cables in situations requiring high AC transmission at high frequencies, such as RIT. [Means for Solving the Problem]

[0023] In a first aspect for better understanding of the present disclosure, there is provided a radio frequency (RF) coaxial cable for use in situations requiring high current alternating current (AC) transmission at high frequencies, the RF coaxial cable comprising a single hollow inner conductor provided with a flexible metal shield.

[0024] In a first variant of the first aspect, the flexible metal shield is preferably formed of a nickel-copper braid or a silver-copper braid.

[0025] In a second variant of the first aspect, the RF coaxial cable preferably further comprises an insulator on the single hollow inner conductor. The insulator is preferably made of silicone rubber, and particularly preferably made of vinyl methyl silicone rubber. It is preferable that the RF coaxial cable further comprises an outer conductor on the insulator, and it is preferable to further comprise: the outer conductor formed from a second flexible metal shield; an outer sleeve on the outer conductor; and an electromagnetic compatibility (EMC) overbraid on the outer sleeve. In this regard, the second flexible metal shield is preferably formed of a nickel-copper braid or a silver-copper braid, and / or the outer sleeve is preferably formed of a non-metallic tubular braid, and / or the EMC overbraid is preferably formed of a nickel-copper braid or a silver-copper braid.

[0026] In a third variant of the first aspect, the single hollow inner conductor is preferably constituted by: a flexible metal shield; and a hollow formed body, wherein the flexible metal shield is provided in a sheath shape on the hollow formed body, thereby maintaining the shape of the flexible metal shield. In the latter case, the hollow formed body is preferably a hollow plastic formed body, particularly preferably an inner tube made of silicone rubber, and most particularly preferably an inner tube made of vinyl methyl silicone rubber.

[0027] In the fourth modification of the first embodiment, it is preferable that a single hollow inner conductor has a diameter d1 selected to provide a low capacitance per unit length of the RF coaxial cable. In the latter case, it is preferable that the low capacitance per unit length is less than 160 pF / m. In addition to or instead of this, it is preferable that d1 is further selected to optimize the relationship between low capacitance per unit length, low power loss, high radial heat dissipation of the RF coaxial cable, and low inductance per unit length. In the latter case, the low power loss is preferably in the range of less than 7.7 W / m, particularly preferably in the range of 2.4 W / m to 6.8 W / m, particularly preferably achieved by making the AC resistance per unit length less than 30.0 mΩ / m at a reference frequency (e.g., 750 kHz), the high heat dissipation is preferably in the range of higher than 1.0 W / K, and the low inductance per unit length is preferably in the range of less than 220 nH / m. In addition to this, or instead, d1 is preferably in the range of 4.0 mm to 8.5 mm, and particularly preferably in the range of 4.5 mm to 8.2 mm.

[0028] In the fifth modification of the first embodiment, the situation is preferably an RF ion thruster, and more preferably a grid-type ion thruster. In the latter case, it is preferable that the situation includes high AC in the range of 25A to 50A peak-to-peak and high frequencies in the range of 500kHz to 900kHz.

[0029] In a second embodiment for better understanding of the present disclosure, a high-frequency (RF) coaxial cable is provided for use in situations requiring high-frequency, high-current alternating current (AC) transmission, comprising: a single hollow inner conductor having a flexible metal shield; an insulator on the single hollow inner conductor; an outer conductor on the insulator, the outer conductor being formed from a second flexible metal shield; an outer sleeve on the outer conductor; and an electromagnetic compatibility (EMC) overbraid on the outer sleeve.

[0030] Furthermore, it is preferable that the second embodiment includes the characteristics of any of the first to fifth improvements of the first embodiment. [Brief explanation of the drawing]

[0031] The technical embodiments of the embodiments described herein will be described with reference to the accompanying drawings. [Figure 1] This shows a system (e.g., a satellite) that includes a coaxial cable connecting an RF AC power supply and a radio frequency ion thruster (RIT). [Figure 2A] This shows a coaxial cable 10pa based on prior art. [Figure 2B] This graph shows the temperature gradient of the cable core / shell plotted on the vertical axis, with the overall outer diameter of the coaxial cable 10pa on the horizontal axis. [Figure 3] Embodiments of the RF supply coaxial cable for electric propulsion according to this disclosure are shown. [Figure 4A] This disclosure shows the relationship between the characteristics of the RF supply coaxial cable for electric propulsion (components used / radius / diameter of layers) and the capacitance obtainable per unit length. [Figure 4B] The characteristics of the RF supply coaxial cable for electric propulsion of this disclosure (components used / radius / diameter of layers), the inductance obtainable per unit length, resistance per unit length, power loss, heat dissipation, and core temperature under a reference flight condition (e.g., space) defined as a solar radiation of 1400 W / m2 and a thermal environment temperature of 30°C in a vacuum are shown. [Figure 5A] The test results for core temperature (measurements taken in a vacuum test chamber (ground-mounted) in a thermal environment of 30°C without solar radiation) are shown for three use cases of the RF supply coaxial cable for electric propulsion described herein, namely OP-1 (low power mode), OP-2 (high current mode), and OP-3 (maximum thrust mode). [Figure 5B]This disclosure presents test results from the perspective of power loss for three use cases of the RF supply coaxial cable for electric propulsion, namely OP-1 (low power mode), OP-2 (high current mode), and OP-3 (maximum thrust mode). [Modes for carrying out the invention]

[0032] The following description provides specific details to give a full understanding of the technology presented herein, for illustrative purposes rather than limitations. Those skilled in the art will see that the technology can also be implemented in other embodiments distinct from these specific details.

[0033] Furthermore, those skilled in the art will recognize that the services, functions, and processes disclosed herein can be implemented using software or application-specific integrated circuits (ASICs), digital signal processors (DSPs), or general-purpose computers that function in conjunction with a programmed microprocessor. Although the following embodiments are described in terms of methods and apparatus, it will also be recognized that the technologies described herein can be embodied in computer programs and systems having a computer processor and memory incorporated into the processor, and that the services, functions, and processes disclosed herein can be recorded in memory by one or more programs that perform them. This applies in particular to the following embodiments: (i) an automated process for manufacturing / forming the loss-optimized RF coaxial cable of the Disclosure, and (ii) a simulation process for the loss-optimized RF coaxial cable of the Disclosure.

[0034] Figure 3 shows an embodiment of the electric propulsion RF supply coaxial cable 10 of the present disclosure used in situations requiring high AC transmission at high frequencies. Generally, the electric propulsion RF supply coaxial cable 10 of the present disclosure employs an alternative approach to existing ones, combining the required reduction of losses (such as power loss) during transmission with a high degree of mechanical flexibility, and further achieving an extremely low temperature gradient between the forward conductor 101a in the core 101 and the cable surface 104.

[0035] To this end, the RF supply coaxial cable 10 for electric propulsion (hereinafter simply referred to as "RF coaxial cable 10") comprises a single hollow inner conductor 101 equipped with a flexible metal shield 101a. That is, for this purpose, a combination of a specific geometric structure and suitable materials (further described below) is used. Instead of a forward conductor 101pa (see Figure 2A) consisting of bundles of many stranded wires 101pa-str, as in conventional RF cables 10pa, a single waveguide / hollow conductor 101 is used. A somewhat similar structure is found only in less relevant technical fields such as fixed conductors, for example, in tubular shapes in antenna technology. This has the advantage that, compared to stranded wires 101pa-str, the aforementioned proximity effect loss between adjacent conductors at the same potential does not occur in the design. Furthermore, the hollow conductor 101 also has the advantage of being able to be designed to be optimal for the current distribution caused by the aforementioned skin effect (e.g., high current density in the edge layer). Therefore, the use of the available conductor cross-sectional area can be maximized, and the amount of conductor material that is unnecessary because current does not flow through it can be minimized. However, the hollow conductor tube 101pa used previously lacks flexibility and is therefore unsuitable for the circumstances of this disclosure; in this case, a flexible metal shield 101a is used.

[0036] In this regard, the flexible metal shield 101a is preferably composed of a nickel-copper braid or a silver-copper braid. This disclosure is not limited to any particular type of braid. Other material combinations based on this disclosure are also feasible. As a non-limiting example, a nickel-plated copper braid with a minimum optical coverage of 93% at temperatures above 150°C can be used.

[0037] Furthermore, it is preferable that the RF coaxial cable 10 further comprises an insulator 102 on a single hollow inner conductor 101 (or more precisely, on a flexible metal shield). It should be noted in this regard that when the Disclosure states that one layer is "on top of" another layer, this should be interpreted as substantially complete area / circumferential contact between the layers. However, this does not limit the method / process of manufacturing such a laminated composite in any form. (i) one layer (e.g., a braid) may cover another layer like a sheath; (ii) one layer, e.g., a (plastic) sleeve, may be laminated with another layer; (iii) one layer, e.g., a (plastic) sleeve, may cover another layer; and (iv) an adhesive / bonding layer (or a similar functional layer, not shown) may be provided between two layers of the Disclosure as needed (in other words, it is not possible to circumvent the scope of protection of the Disclosure by sandwiching one or more adhesive layers or similar functional layers between two layers as defined in the Disclosure).

[0038] Furthermore, the insulator 102 is preferably made of silicone rubber, and more preferably vinyl methyl silicone rubber. In addition, it is preferable that the RF coaxial cable 10 further comprises (i) an outer conductor 103 on the insulator 102, the outer conductor 103 preferably forming a second flexible metal shield 103, (ii) an outer sleeve 104 on the outer conductor 103, and (iii) an EMC overbraid 105 on the outer sleeve 104.

[0039] In this regard, the second flexible metal shield 103 is preferably made of a nickel-copper braid or a silver-copper braid.

[0040] In addition to or instead of this, the outer sleeve 104 is preferably made of a non-metallic tubular braid. In non-limiting examples, the non-metallic tubular braid may be a flame-retardant fabric made of a meta-aramid material, a para-aramid material (Kevlar (Kevlar is a registered trademark of DuPont de Nemours, Inc.)), or other insulating material.

[0041] In addition to or instead of this, the EMC overbraid 105 is preferably made of a nickel-copper braid or a silver-copper braid (as described above).

[0042] Furthermore, a single hollow inner conductor 101 (i.e., within a single hollow inner conductor 101 there are no further features other than those described below) is preferably composed of a flexible metal shield 101a and a hollow forming body 101b, and it is preferable that the flexible metal shield 101a is provided in a sheath-like manner on the hollow forming body 101b to maintain the shape of the flexible metal shield 101a. As mentioned above, although it is practical to cover the hollow forming body 101b with the flexible metal shield 101a, this does not preclude any other feasible manufacturing method for forming a single hollow inner conductor 101, such as plating or weaving.

[0043] In this regard, the hollow molded body 101b is preferably a hollow plastic molded body, particularly preferably an inner tube made of silicone rubber, and most preferably an inner tube made of vinylmethyl silicone rubber. That is, in order to maintain the position of the flexible metal shield 101a in the overall structure of the RF coaxial cable 10, it is preferable that the shield 101a is placed on the plastic molded body 101b. In order to minimize the bending rigidity of the overall structure of the RF coaxial cable 10, it is preferable that the molded body 101b is hollow.

[0044] Furthermore, it goes without saying that it is preferable that the single hollow inner conductor 101 (hollow formwork 101b and flexible metal shield 101a), the insulator 102, the outer conductor 103, the outer sleeve 104, and the EMC overbraid 105 all have a concentric (effectively) cylindrical shape with respect to a common center, as is common in coaxial cables. For this reason, the hollow formwork 101b has a radius r0 or diameter d0, the flexible metal shield 101a (or the single hollow inner conductor 101 as a whole) has a radius r1 or diameter d1, the insulator 102 has a radius r2 or diameter d2, the outer conductor 103 has a radius r3 or diameter d3, the outer sleeve 104 has a radius r4 or diameter d4, and the EMC overbraid 105 has a radius r5 or diameter d5.

[0045] In this regard, it is preferable that the single hollow inner conductor 101 has a diameter d1 selected to result in a low capacitance per unit length of the RF coaxial cable 10. Another drawback of conventional RF cables 10pa is that the overall outer diameter d0 is often small, which affects the temperature generated during operation (see Figure 2A). On the one hand, reducing the diameter is essential to ensure the mechanical flexibility of the cable. However, on the other hand, this constraint means that the resulting small diameter of the inner conductor leads to an extremely small contact surface with the adjacent layer (insulating material / insulator 102pa). As a result, the heat generated in the output conductor / inner conductor 101pa can only be dissipated to a limited extent to the outside, resulting in "heat accumulation" within the cable core 101pa and creating a high temperature gradient between the core 101pa and the surface of the RF coaxial cable 10pa (e.g., outer sleeve 104). Therefore, a notable feature of the RF coaxial cable 10 of this disclosure lies in the selected diameter d1 of the flexible metal shield 101a. The diameter d1 is designed to achieve a compromise / optimal balance between low power loss, good / high radial heat dissipation, and low capacitance per unit length of the RF coaxial cable 10. This low capacitance per unit length is particularly important in the context of the present disclosure, namely, the context of an RF ion thruster (particularly preferably a grid-type ion thruster) (as a resonant circuit). This environment preferably involves high AC with peak-to-peak currents of 25A to 50A and high frequencies in the range of 500kHz to 900kHz.

[0046] Figure 4A shows the relationship between the characteristics of the RF supply coaxial cable for electric propulsion of this disclosure (components used / radius / diameter of layers) and the capacitance obtainable per unit length. On the other hand, Figure 4B shows the characteristics of the RF supply coaxial cable for electric propulsion of this disclosure (components used / radius / diameter of layers) and the capacitance obtainable in a vacuum of 1400 W / m 2 This shows the inductance, resistance, power loss, heat dissipation, and core temperature per unit length obtained under defined reference flight conditions (e.g., space) with solar radiation and a thermal environment temperature of 30°C.

[0047] As shown in Figures 4A and 4B, Comparative Examples 1 to 7 (abbreviated as "CE1" to "CE7") exhibit characteristics r0 to r5 (d0 to d5), where the capacitance per unit length, inductance per unit length, resistance per unit length, power loss, heat dissipation (e.g., heat dissipation between the inner core conductor and the insulating material), and core temperature are below or above the claimed range (highlighted with black squares in Figures 4A and 4B). Next, Embodiments 1 to 10 (abbreviated as "EMB1" to "EMB7") exhibit characteristics r0 to r5 (d0 to d5) where the capacitance per unit length, inductance per unit length, resistance per unit length, power loss, heat dissipation (e.g., heat dissipation between the inner core conductor and the insulating material), and core temperature are within the claimed range. In particular, both Embodiment 10 (EMB10) and Comparative Example 7 (CE7) are special in that they represent extreme cases where d5 is 25.0 mm, that is, they show the maximum allowable outer diameter of the RF cable 10 for RIT applications.

[0048] As shown in Figure 4A, it is desirable that the low capacitance per unit length be less than 160 pF / m.

[0049] As shown in Figures 4A and 4B, it is preferable that the diameter d1 (of the single hollow inner conductor 101 / flexible metal shield 101a) is further selected to optimize the relationship between low capacitance per unit length, low power loss, high radial heat dissipation of the RF coaxial cable 10, and low inductance per unit length. That is, as shown in Figure 4B (and below in Figure 5B), the low power loss is preferably in the range of less than 7.7 W / m, more preferably in the range of 2.4 W / m to 6.8 W / m (for example, depending on the thruster operating point (OP), preferably less than 7.7 W / m at all OPs (see Figures 4A and 4B above)), the high heat dissipation is preferably in the range of more than 1.0 W / K, and the low inductance per unit length is in the range of less than 220 nH / m.

[0050] As shown in Figures 4A and 4B, it is preferable that the diameter d1 (of the single hollow inner conductor 101 / flexible metal shield 101a) be further selected to optimize the relationship between low resistance per unit length and low core temperature (for the latter, see also Figure 5A in different scenarios). Specifically, the low resistance per unit length is preferably in the range of less than 30.0 mΩ / m at a reference frequency (e.g., 750 kHz), which enables low power loss. The low core temperature is preferably in the range of less than 170°C (reference flight conditions, i.e., 1400 W / m in a vacuum). 2 Outer space is defined as having no solar radiation and a thermal environment temperature of 30°C (see Figure 4B), or a range of less than 120°C (meaning no solar radiation and measurements being taken in a vacuum test chamber (located on the ground) and a thermal environment temperature of 30°C; see Figure 5A).

[0051] Ultimately, the important parameter d1 (diameter of the single hollow inner conductor 101 / flexible metal shield 101a) is preferably in the range of 4.0 mm to 8.5 mm, and particularly preferably in the range of 4.5 mm to 8.2 mm (as shown in bold in Figure 4A).

[0052] Figure 5A shows the test results for core temperature (measurements taken in a vacuum test chamber (installed on the ground) in a thermal environment of 30°C without solar radiation) for three use cases of the RF coaxial cable 10 of this disclosure, namely OP-1 (low power mode), OP-2 (high current mode), and OP-3 (maximum thrust mode). On the other hand, Figure 5B shows the test results from the perspective of power loss for the three use cases of the RF coaxial cable 10 of this disclosure, namely OP-1 (low power mode), OP-2 (high current mode), and OP-3 (maximum thrust mode).

[0053] Figures 5A and 5B show two samples, respectively (named "Experimental Circuit Boards (BB)," i.e., prototype models created for test purposes as "Experimental Circuit Boards"), labeled "BB#1" and "BB#2" for the RF coaxial cables 10 being evaluated, compared to the prior art RF synchronous cable 10pa (referred to as "Con" for the conventional type). As shown in Figure 5A, samples BB#1 and BB#2 were comparatively superior to the prior art in maintaining the core temperature of the inner conductor 101 below 120°C in all three use cases (excluding ambient influences such as solar radiation). Furthermore, as shown in Figure 5B, samples BB#1 and BB#2 were comparatively superior to the prior art in maintaining the overall power loss of the RF coaxial cable 10 below 7.7 W / m in all three use cases (in all of the above operations).

[0054] In other embodiments, the RF coaxial cable 10 used in situations requiring high AC transmission at high frequencies (i.e., the RF coaxial cable 10 has no further features other than those described below) may be configured as follows: a single hollow inner conductor 101 (preferably including any of the above features) having a flexible metal shield 101a (preferably including any of the above features); an insulator 102 (preferably including any of the above features) on the single hollow inner conductor; an outer conductor 103 (preferably including any of the above features) on the insulator, wherein the outer conductor is formed from a second flexible metal shield (preferably including any of the above features); an outer sleeve 104 (preferably including any of the above features) on the outer conductor; and an EMC overbraid 105 (preferably including any of the above features) on the outer sleeve.

[0055] The advantages of the technology described herein are expected to be fully understood from the foregoing description, and it is evident that various modifications can be made to the form, structure, and arrangement of the exemplary embodiments without departing from the scope of this disclosure or without impairing any of its advantageous effects. Since the technology described herein can be modified in various ways, it is recognized that this disclosure should be limited only to the scope of the claims set forth below. [Explanation of symbols]

[0056] 1 System 10. High-frequency (RF) coaxial cable 10pa coaxial cable 20. High-frequency ion thruster (RIT) 30 RF AC power supply 101 Single hollow inner conductor 101a Flexible metal shield 101b Hollow formation 101pa core 101pa-str stranded wire 102 Insulator 102pa insulator 103 Outer conductor 103pa outer conductor 104 Outer sleeve 104pa outer sleeve 105 Electromagnetic Compatibility (EMC) Overblade BB experimental circuit board CE comparison example EMB Embodiment d0 diameter d1 diameter d s diameter OP operating point r1 characteristics r2 characteristics r3 characteristics r4 characteristics r5 characteristics

Claims

1. A high-frequency (RF) coaxial cable (10) used in situations requiring high-frequency, high-current alternating current (AC) transmission, An RF coaxial cable characterized by comprising a single hollow inner conductor (101) having a flexible metal shield (101a).

2. The RF coaxial cable according to claim 1, characterized in that the flexible metal shield is made of a nickel-copper braid or a silver-copper braid.

3. The RF coaxial cable according to claim 1, further comprising an insulator (102) on the single hollow inner conductor.

4. The RF coaxial cable according to claim 3, characterized in that the insulator is made of silicone rubber, preferably vinylmethyl silicone rubber.

5. The RF coaxial cable, The outer conductor (103) on the insulator, wherein the outer conductor is formed from a second flexible metal shield, The outer sleeve (104) on the outer conductor, The electromagnetic compatibility (EMC) overblade (105) on the outer sleeve and The RF coaxial cable according to claim 3, further comprising the features described above.

6. The second flexible metal shield consists of a nickel-copper braid or a silver-copper braid, and / or The outer sleeve is made of a non-metallic tubular braid and / or, The RF coaxial cable according to claim 5, characterized in that the EMC overbraid consists of a nickel and copper braid or a silver and copper braid.

7. The single hollow inner conductor is The aforementioned flexible metal shield, and The RF coaxial cable according to claim 1, characterized in that it is composed of a hollow forming body (101b) on which the flexible metal shield is provided in a sheath-like manner, thereby maintaining the shape of the flexible metal shield.

8. The RF coaxial cable according to claim 7, characterized in that the hollow forming body is a hollow plastic forming body, preferably an inner tube made of silicone rubber, and particularly preferably an inner tube made of vinylmethyl silicone rubber.

9. The diameter d of the single hollow inner conductor is selected such that it has a low capacitance per unit length of the RF coaxial cable. １ The RF coaxial cable according to claim 1, characterized by having the following features.

10. The RF coaxial cable according to claim 9, characterized in that the low capacitance per unit length is less than 160 pF / m.

11. d １ The RF coaxial cable according to claim 9, further selected such that the relationship between low capacitance per unit length, low power loss, high radial heat dissipation of the RF coaxial cable, and low inductance per unit length is optimized.

12. The low power loss is in the range of less than 7.7 W / m, preferably in the range of 2.4 W / m to 6.8 W / m, and particularly preferably achieved by setting the AC resistance per unit length at the reference frequency to less than 30.0 mΩ / m. The aforementioned high heat dissipation is in a range higher than 1.0 W / K. The RF coaxial cable according to claim 11, characterized in that the low inductance per unit length is in the range of less than 220 nH / m.

13. d １ The RF coaxial cable according to claim 9, characterized in that the length is in the range of 4.0 mm to 8.5 mm, preferably in the range of 4.5 mm to 8.2 mm.

14. The RF coaxial cable according to claim 1, characterized in that the aforementioned situation is an RF ion thruster, preferably a grid-type ion thruster.

15. The aforementioned situation is, High AC in the range of 25A to 50A at peak-to-peak, The RF coaxial cable according to claim 14, characterized in that it includes high frequencies in the range of 500 kHz to 900 kHz.

16. A high-frequency (RF) coaxial cable (10) used in situations requiring high-frequency, high-current alternating current (AC) transmission, A single hollow inner conductor (101) having a flexible metal shield (101a), The insulator (102) on the single hollow inner conductor, The outer conductor (103) on the insulator, wherein the outer conductor is formed from a second flexible metal shield, The outer sleeve (104) on the outer conductor, and An RF coaxial cable characterized by being composed of an electromagnetically compatible (EMC) overbraid (105) on the outer sleeve.

17. The RF coaxial cable according to claim 16, characterized in that it is configured to have the characteristics of claim 2.

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