Transmission line, and pulse forming circuit and pulse power supply device using said transmission line

Abstract

To provide a transmission line for pulse waveform shaping which can further advance miniaturization of a device, and a pulse forming circuit and a pulse power supply device which use the transmission line.SOLUTION: A transmission line which includes first and second conductors constituting a coaxial cylindrical line or a parallel flat plate line and is used for pulse waveform shaping is configured such that the first conductor is arranged and insulating fluid is filled in the tube of the second conductor, the inside of the tube and the first conductor excluding the end portions of the transmission line are covered with a single insulating fluid, the cross-sections of the end portions are spread while the impedance of the end portions of the transmission line is matched with the impedance of portions other than the end portions, whereby creeping discharge at the end portions is suppressed when a high voltage pulse is applied, thereby preventing dielectric breakdown, and the diameter of the transmission line excluding the end portions thereof is reduced.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a transmission line for forming a pulse, and a pulse forming circuit and a pulse power supply device using the transmission line. [Background technology]

[0002] In recent years, technology (also called "pulse power technology") has been developed and utilized to generate high-power, high-voltage pulses with short pulse widths on the order of picoseconds (ps) or nanoseconds (ns) for various applications. In order to generate high-power, high-voltage pulses with short pulse widths, circuits called pulse wave forming circuits or pulse forming circuits are often used. Among these, circuits using a transmission line structure that can handle high voltage and large current are often used, particularly when generating high-power, high-voltage pulses. For example, Patent Document 1 discloses a pulse power supply that uses a Blumlein transmission line, which is a distributed constant line, to form a pulse.

[0003] Patent Document 2 discloses a pulse generating circuit (pulse forming circuit) that includes a Blumlein line connected to a charging power source and a switching element, and generates a rectangular wave pulse to a load connected to the Blumlein line, and discloses a pulse generating device in which the Blumlein line is configured by multiple spiral lines arranged in a conductive cylinder, and the thickness of the conductor that configures the end of the spiral line is made thicker than the thickness of the conductor in the center of the spiral line. Patent Document 2 describes a problem that when a Blumlein line is configured by a conductive cylinder and a double spiral line to solve the problem that a pulse forming line using a Blumlein line requires a line length of several tens of meters to obtain a pulse width of several hundreds of nanoseconds, and that the width of the hollow part of the Blumlein line needs to be very large to match the impedance with a high impedance load, the insulation breakdown of the insulating medium filled in the cylindrical conductor is likely to occur, and describes that the pulse generating circuit proposed in Patent Document 2 solves this problem.

[0004] Patent Document 3 describes that, as shown in FIG. 7(B), in a pulse power supply using a Blumlein BL, the Blumlein BL has a capacitor configuration in which two layers of terminals ab and ac to which a high-voltage pulse is applied are laminated, and that there is a problem that the length and diameter of the Blumlein become very large in order to increase the capacity for a large-current pulse output. In response to this problem, Patent Document 3 discloses a pulse power supply as shown in FIG. 7(A), for example. This pulse power supply applies a high-voltage pulse from a capacitor C0 initially charged by a high-voltage charger (HV Charger) to the primary side of a saturable transformer ST through a saturable reactor SI and a semiconductor switch SW, charges a pulse forming line PFL (a distributed constant line for forming a pulse) with a large current I1 due to the step-down operation of the saturable transformer ST, and supplies a current pulse I2 (large current, ultrashort pulse) to a load LOAD through a diode D due to the magnetic switch operation of the saturable transformer ST. The pulse forming line PFL has an inner cylindrical electrode P1 and an outer cylindrical electrode P2 that is coaxial with the inner cylindrical electrode P1, and is filled with deionized water, insulating oil, or a medium with a high dielectric constant as a magnetic material between the electrodes P1 and P2, and is equivalent to a distributed constant line in which a capacitance component C1 is formed in the radial direction and an inductance component L1 is formed in the longitudinal direction per unit length, and is structured to be capable of shaping into a steep waveform with a relatively short pulse width (several tens to several hundreds of ns).Patent Document 3 describes that the electrode shape of the pulse forming line PFL can also be a parallel plate configuration in which the electrodes P1 and P2 face each other to form a distributed constant line. Furthermore, Patent Document 3 discloses a configuration in which, instead of the pulse forming line PFL, a pulse forming network PFN having an LC lumped constant circuit configuration in which capacitors C1-1 to C1-N and an inductor L are connected in multiple stages in a ladder shape is provided, and it is described that, like the pulse forming line PFL, this is equivalent to a distributed constant line, making it possible to shape the pulse into a steep waveform with a relatively short pulse width. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-130443 [Patent Document 2] Japanese Patent Application Publication No. 4-326809 [Patent Document 3] JP 2004-350338 A [Non-patent literature]

[0006] [Non-Patent Document 1] Osamu Yamamoto and Masashi Hamada (co-editors), "OHM University Textbook: High Voltage Engineering," Ohmsha Co., Ltd., 2013, pp. 128-135 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, Patent Document 3 also describes the use of a pulse forming network (PFN) configured as an LC lumped constant circuit. However, when dealing with high voltages of approximately 100 kV (kilovolts) or more, lumped constant elements with high withstand voltages are not available, and in fact, it has not been possible to adopt a pulse forming network consisting of an LC lumped constant circuit. Furthermore, there is a need to further miniaturize the device compared to the technology disclosed in Patent Document 3.

[0008] Therefore, the present invention has been devised in consideration of the above-mentioned problems, and an object of the present invention is to provide a transmission line for pulse formation that enables further miniaturization of devices that generate high-output, high-voltage pulses, and a pulse forming circuit and a pulse power supply device that use the transmission line. [Means for solving the problem]

[0009] According to the present invention, there is provided a transmission line used for a pulse wave forming type having first and second conductors constituting a coaxial cylindrical line or a parallel plate line, the first conductor is disposed in a tube of the second conductor and filled with an insulating fluid, the inside of the tube other than the end of the transmission line and the first conductor are covered with a single insulating fluid, the impedance of the end of the transmission line is matched with the other end, and the cross section of the end is expanded to suppress creeping discharge at the end when a high voltage pulse is applied, preventing insulation breakdown, and reducing the diameter of the other end of the transmission line to make it smaller. Also, according to the present invention, there is provided a pulse forming circuit and a pulse power supply device using the above transmission line. Effect of the Invention

[0010] According to the present invention, it is possible to further reduce the size of a transmission line, and to further reduce the size of a pulse forming circuit and a pulse power supply device that use the transmission line. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 illustrates an exemplary embodiment of the present invention. [Diagram 2] 1A and 1B are diagrams illustrating simulation results of an exemplary embodiment of the present invention. [Diagram 3] 1A to 1C are diagrams illustrating an exemplary embodiment of the present invention. [Figure 4] 1A and 1B are diagrams illustrating an exemplary embodiment of the present invention. [Diagram 5] 1A to 1C are diagrams illustrating an exemplary embodiment of the present invention. [Figure 6] 1A and 1B are diagrams illustrating an exemplary embodiment of the present invention. [Figure 7] 1A and 1B are diagrams illustrating an example of related art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An exemplary embodiment of the present invention will be described. According to the embodiment of the present invention, in a pulse forming circuit (pulse wave forming circuit) using a transmission line used when generating a high-power high-voltage pulse, a transmission line for pulse formation (pulse wave forming type) (e.g., 100 in FIG. 1, 300 in FIG. 3, etc.) includes first and second conductors (e.g., 102 and 101 in FIG. 1, 301 and 302 in FIG. 3, etc.) extending from one end in the longitudinal direction to the other end while being spaced apart from each other, and the end portions (e.g., 1, 306, 307, etc.) and a portion other than the end of the transmission line (e.g., thin-diameter tube 107 in FIG. 1, intermediate portion 308 in FIG. 3, etc.), while the size of the end face defined by at least one of the first and second conductors at the end (114, 115 in FIG. 1, 306, 307 in FIG. 3, etc.) is made larger than the cross section of the portion other than the end of the transmission line. According to the present invention, the first conductor (e.g., 102 in FIG. 1, 301 in FIG. 3, etc.) is accommodated in the tube of the second conductor (e.g., 101 in FIG. 1, 302 in FIG. 3, etc.) and is filled with an insulating fluid (303 in FIG. 3), and the inside (inner wall) of the tube of the second conductor other than the end of the transmission line and the first conductor are covered with a single insulating fluid (e.g., 303 in FIG. 3), and there is no triple point (a point where the interface between two types of dielectrics intersects with an electrode (conductor)) other than the end of the transmission line, making it possible to reduce the diameter other than the end. In other words, by expanding the cross section of the end of the transmission line, creeping discharge at the end is suppressed and insulation breakdown is prevented when a high-voltage pulse (e.g., about 100 kV (kilovolts) or more) that cannot be handled by a pulse forming network (PFN) that is an LC lumped constant circuit is applied, and the diameter of the transmission line other than the end is reduced to make it smaller.

[0013] 1 is a diagram illustrating a transmission line according to an embodiment of the present invention. The transmission line 100 according to the embodiment is configured as a coaxial cylindrical line including an outer conductor 101 (second conductor) that extends in the longitudinal direction from one end of the transmission line 100 to the other end and constitutes an outer cylindrical electrode, and an inner conductor 102 (first conductor) that is disposed inside the outer conductor 101 coaxially with the outer conductor 101 and extends in the longitudinal direction from one end of the transmission line 100 to the other end and constitutes an inner cylindrical electrode.

[0014] At both ends 114, 115 in the longitudinal direction of the transmission line 100 (coaxial cylindrical line), the outer conductor 101 is configured as tapered tubes 105, 106.

[0015] The outer conductor 101 in the middle between the end portions 114, 115 on both sides is configured as a thin-diameter tube 107 whose bore is smaller than the bore of the end faces of the tapered tubes 105, 106.

[0016] That is, the outer conductor 101 of the end 114 of the coaxial cylindrical line is configured as an inverted truncated cone-shaped tapered tube 105 that gradually widens (expands in diameter) from the connection portion with the thin-diameter tube 107 on the other side of the end 114 that faces the end face (opening) on ​​one side of the end 114 toward the end face (opening) on ​​one side of the end 114.

[0017] An insulating cover 110 and an input port 103 are disposed at the opening of the tapered tube 105 at the end face of the end portion 114 .

[0018] The insulating lid 110 seals the insulating fluid (liquid, gas, etc.) filled in the gap between the outer conductor 101 and the inner conductor 102. The input port 103 is connected to the transformer secondary side of the pulsed power supply (for example, the secondary side of the saturable transformer ST in FIG. 7(A)).

[0019] The outer conductor 101 of the end 115 of the coaxial cylindrical line is configured as an inverted truncated cone-shaped tapered tube 106 that gradually widens (expands in diameter) from the connection between the end face (opening) on ​​one side of the end 115 and the thin-diameter tube 107 on the other side of the end 115 that faces the end face (opening) on ​​one side of the end 115.

[0020] An insulating cover 111 and an output port 104 are disposed at the opening of the tapered tube 106 .

[0021] Similar to the insulating lid 110, the insulating lid 111 seals an insulating fluid (liquid or gas) or the like filled in the gap between the outer conductor 101 and the inner conductor 102. The output port 104 is connected to a load (for example, the load LOAD in FIG. 7(A)).

[0022] In FIG. 1, the outer conductor 101 of the small diameter tube 107 has 180-degree bent portions 116 and 117, but the number of bent portions is not limited to two. By bending the transmission line 100 by 180 degrees, the dimension between both ends of the transmission line is reduced compared to the case where the transmission line 100 is formed of a straight tube. In the small diameter tube 107, the bent portions 116 and 117 constituting the outer conductor 101 have a predetermined radius and are connected to the straight tube outer conductor 101 at both ends. The bent portions 116 and 117 may be connected by, for example, impedance matching the bent joint to the straight tube cylindrical conductor (outer conductor 101) with a connecting tool or the like, or may be connected by brazing or the like. Alternatively, they may be molded integrally with the straight tube cylindrical conductor by bending or the like. The inner conductor 102 is bent into an arc shape coaxially with the outer conductor 101 at the bent portions 116 and 117. At the ends 114, 115, the tapered tubes 105, 106 may be connected to the straight cylindrical conductor of the small diameter tube 107 by impedance matching using a connector or the like, or may be connected by brazing or the like, or may be integrally molded.

[0023] The diameter of the inner conductor 108 of the end 114 matches the diameter of the inner conductor 102 in the thin tube 107 on the side connected to the inner conductor 102 of the thin tube 107, and is deformed toward the input port 103 provided on one end face of the end 114 while maintaining impedance matching in accordance with the shape of the tapered tube 105 of the outer conductor 101. That is, the inner conductor 108 of the end 114 is formed into an inverted truncated cone shape whose diameter gradually increases from the other side facing the one end face of the end 114 toward the input port 103 on the one end face of the end 114.

[0024] Similarly, the inner conductor 109 of the end 115 matches the diameter of the inner conductor 102 in the thin tube 107 on the side connected to the inner conductor 102 of the thin tube 107, and is deformed toward the output port 104 provided on one end face of the end 115 in accordance with the shape of the tapered tube 106 of the outer conductor 101 while maintaining impedance matching. That is, the inner conductor 109 of the end 115 is formed into an inverted truncated cone shape that gradually expands in diameter from the other side facing the one end face of the end 115 toward the output port 104 on one end face of the end 115. Note that the tapered tubes 105, 106 and the inner conductors 108, 109 are configured such that the line connecting the center of the bottom face and the center of the top face of the inverted truncated cone intersects with the bottom face and the top face at an angle, but the angle of inclination is not limited to the example shown in FIG. 1, and the line connecting the center of the bottom face and the center of the top face of the inverted truncated cone may be configured to intersect with the bottom face and the top face at a right angle.

[0025] The internal conductors 108 and 109, which are expanded at the ends 114 and 115, may be hollow conductors, i.e., pipe-shaped conductors. By making them pipe-shaped conductors, the shape can be processed not only by cutting but also by drawing or the like. Also, by making them pipe-shaped, the weight of the conductor can be reduced. In this case, a through hole having a size sufficiently smaller than the wavelength corresponding to the frequency of the pulse transmitted by the transmission line 100 (for example, 1 / 5 wavelength or less) may be opened on the side of the pipe so that the insulating fluid can enter the inside of the pipe. Note that the number of through holes is not limited to one. By opening holes at multiple locations on the side of the pipe, it is possible to reduce the amount of air remaining inside the pipe. For example, the pipe may be made of a material such as a mesh having many through holes of the above size on its side. This further reduces the amount of air remaining inside. The internal conductor 102 housed in the small diameter tube 107 (external conductor) may also be a hollow cylindrical conductor (pipe-shaped) with a through hole of the above size on the side of the pipe.

[0026] As a method of impedance matching, in the case of a coaxial cylindrical line, for example, the ratio of the inner diameter of the outer conductor to the outer diameter of the inner conductor is made constant. If the outer diameter of the inner conductor 102 of the coaxial cylindrical line is a and the inner diameter of the outer conductor 101 is b, the characteristic impedance Z0 per unit length of the coaxial line is given by 1 / (2π)√(μ / ε)ln(b / a)[Ω] where ε is the dielectric constant of the dielectric material inside the coaxial cylindrical line, and μ is the magnetic permeability of the conductor.

[0027] Therefore, if the inner diameter (inner radius) of outer conductor 101 of thin tube 107 is b1, the outer diameter (outer radius) of inner conductor 102 accommodated in thin tube 107 (outer conductor) is a1, the inner diameter (inner radius) of tapered tubes 105, 106 between one end and the other end of end portions 114, 115 is bx, the outer diameter (outer radius) of inner conductors 108, 109 is ax, the maximum inner diameter (inner radius) of tapered tubes 105, 106 at the open end on the other side of end portions 114, 115 is b2, and the maximum outer diameter (outer radius) of inner conductors 108, 109 is a2, then b1 / a1=bx / ax=b2 / a2 If so, the characteristic impedance Z0 of the tapered tubes 105, 106 at the ends 114, 115 of the transmission line 100 and the small diameter tube 107 therebetween remains unchanged, and impedance matching is achieved between the ends 114, 115 of the transmission line 100 and other locations.

[0028] Of course, the impedance matching method is not limited to the above. For example, when impedance matching is performed using a quarter-wavelength line, a step shape (step) may be used. A quarter-wavelength transmission line has the property of converting the load impedance into an inverse number. However, when impedance matching is performed in a wide frequency band that forms a pulse, it is preferable to use tapered tubes 105 and 106 as shown in Figure 1.

[0029] Although not particularly limited, in this embodiment, impedance matching refers to a state in which the voltage standing wave ratio is 1.3 or less, preferably 1.2 or less, and more preferably 1.05 or less, for example.

[0030] The waves propagating through the coaxial cylindrical line are fundamental mode TEM (Transverse Electromagnetic) waves (the components in the propagation direction of the electric and magnetic fields are 0), but as the frequency increases, higher modes occur. Therefore, it is desirable to set the diameters of the tapered tubes 105 and 106 (for example, the inner radius R of the end faces) within a range that can suppress the occurrence of higher modes.

[0031] In other words, when the frequency of the transmitted wave becomes high, a TE, for example, appears in the coaxial cylindrical line. 11 Higher modes such as the transverse electric mode occur. Here, the electric field and magnetic field of the electromagnetic wave traveling in the z direction with the longitudinal direction of the coaxial cylindrical line as the z axis are expressed as follows: E = E(x,y)exp(iωt-γz), H = H(x,y)exp(iωt-γz) (ω is the angular frequency), the TE of a hollow cylindrical tube (radius R) is mn The mode is the derivative j of the mth order Bessel function. m 'nth zero j mn 'For (m=0,1,2,…, n=1,2,…), k=j mn ' / R=k mn , Where k 2 =ω 2 εμ+γ 2 (ε is the permittivity, μ is the permeability, γ 2 <0, i.e., when γ is an imaginary number, it travels in the z direction as a wave.) Therefore, k 11 2 =(j 11 ' / R) 3 ≧ω 2 εμ If so, then γ 2 ≧0, and TE 11 The occurrence (progression) of the mode is suppressed. In this case, the diameter range of the tapered tubes 105 and 106 is as follows: R ≤ j 11 ' / {ω√(εμ)} 1 / √(εμ) is the speed of a traveling wave (electromagnetic wave), and the speed in a vacuum is c=1 / √(ε0μ0)(=3×108 The frequency f is approximated by ([m]). For example, let the frequency f be 100 MHz (Mega Hertz). 1 / ω√(εμ) is c / (2πf), and c / f is the wavelength. 11 Since '=1.841, R≦1.841×3×10 8 / (6.28×10 8 )=0.879[m]. Therefore, the higher mode TE 11 The inner radius b2 at the end face of the taper tubes 105, 106 that suppress the generation of noise is calculated to be approximately 88 cm or less, but in reality it becomes smaller depending on the relative dielectric constant of the dielectric. For example, the relative dielectric constant εr of water is approximately 80 at a temperature of 20°C and in a static electric field (this varies depending on temperature and frequency). In this case, the maximum value of the inner radius b2 at the end face of the taper tubes 105, 106 is approximately 10 to 15 cm (diameter: approximately 20 to 30 cm) from 88 [cm] / √εr. However, the above values ​​are merely examples roughly calculated to facilitate understanding of the invention, and of course do not limit the present invention.

[0032] A dielectric is filled in the gap between the inside of the outer conductor 101, which is composed of the tapered tubes 105 and 106 and the small diameter tube 107, and the surface of the inner conductor 102, and the gap is sealed with insulating covers 110 and 111 at both ends of the transmission line 100. As the dielectric, for example, insulating gas such as SF6 (sulfur hexafluoride), which has a high dielectric strength, pure water, pure water mixed with an organic polymer, insulating liquid such as insulating oil or silicone oil, etc. can be used. By mixing an organic polymer into pure water, it is possible to suppress the deterioration of the dielectric strength over time caused by ions dissolving from the wall. In addition, by mixing an organic polymer into pure water, it is possible to increase the viscosity of the insulating liquid without deteriorating the dielectric strength of the insulating liquid. This makes the support of the conductor covered with a single insulating fluid, other than the end of the transmission line, stronger, and increases the resistance to vibration and impact. Similarly, silicone oil, which can be selected from a variety of viscosities, has the same advantages. Dielectrics made of these insulating fluids can be easily filled into the complex interior of a coaxial cylindrical tube without defects such as voids. Thermoplastic resins (such as high-density polyethylene, polystyrene, and fluororesins) that are in a liquid state when filled can also be used as dielectrics.

[0033] The insulating lids 110 and 111 may be made of resin, ceramic, or the like, from the standpoint of airtightness and sealing ability for sealing the insulating fluid (liquid, gas) to be enclosed.

[0034] Since the insulating fluid and the insulating covers 110 and 111 have different dielectric constants, the shapes of the input port 103 and the output port 104 are complex. A pulse transformer or gap switch (not shown) is connected to the outside of the input port 103 and the output port 104, or a pulse forming line is intentionally configured as an open end. A gap switch that adjusts the operating voltage by adjusting the electrode gap distance is used for pulse discharge by the capacitor. The basic principle of the gap switch is to realize high-speed current flow by utilizing the dielectric breakdown of the insulator (e.g. gas) between opposing electrodes.

[0035] The end faces (open ends) of the tapered tubes 105, 106 and the opposite end are connected to a thin tube 107, and the end faces (open ends) of the tapered tubes 105, 106 are hermetically sealed with insulating covers 110, 111 made of a solid insulating material such as resin or ceramic.

[0036] Edges 112, 113 of insulating lids 110, 111 form a triple junction (a point where a conductor and two insulators with different dielectric constants intersect at one point) where three types of materials come into contact: tapered tubes 105, 106 (outer conductor 101), a dielectric that is an insulating fluid, and an insulating material that constitutes insulating lids 110, 111. This triple junction is considered to be prone to dielectric breakdown (to be the starting point of dielectric breakdown) (see Non-Patent Document 1).

[0037] Moreover, it is said that creeping discharge is likely to occur on the surfaces of the insulating covers 110 and 111, which are made of solid insulating material. Creeping discharge is discharge that occurs along the boundary surface of an insulator in a composite insulator such as a solid insulator and a gas insulator. When insulation breakdown occurs due to creeping discharge, the inner conductor 108 and tapered tube (outer conductor) 105, and the inner conductor 109 and tapered tube 106 (outer conductor) become conductive, and no longer function as a transmission line.

[0038] Therefore, in related technology, a method has been adopted in which the desired dielectric strength is designed by the separation distance between the inner conductor and the outer conductor connected to the input port and output port at the end, and the distance is connected with a straight coaxial pipe of the same diameter (see Figure 7(A)). This characteristic is unique to transmission lines that handle high voltage pulses of, for example, about 100kV (kilovolts) or more, and cannot be handled by, for example, a pulse forming network (PFN) that is an LC lumped constant circuit, and is not taken into consideration in transmission lines for low voltage signals that are generally available on the market, for example, coaxial cables that transmit microwave signals, for which a dielectric strength of about 1kV is sufficient.

[0039] According to this embodiment, at ends 114, 115 of the transmission line 100, the outer conductor 101 is made into tapered tubes 105, 106, and the inner conductors 108, 109 are formed accordingly while maintaining impedance matching, so that the end opening surface where dielectric breakdown is likely to occur has a large diameter, a sufficient distance is provided between the outer conductor and the inner conductor, and a sufficient dielectric strength is ensured.

[0040] On the other hand, the intermediate portion between the tapered tubes 105 and 106 is structured so as not to generate a triple point, and the small diameter tube 107 can be made smaller while maintaining the dielectric strength.

[0041] Furthermore, when transmitting a high-voltage pulse (e.g., 100 kv (kilovolt) or more), impedance matching is achieved between tapered tubes 105, 106 and thin tube 107, so that unintended reflected waves are not generated and the tube functions as a transmission line for transmitting the pulse.

[0042] FIG. 2 shows the results of an electromagnetic field simulation performed on a transmission line with a configuration similar to that of FIG. 1. Pure water was assumed as the dielectric. FIG. 2(A) shows an input pulse to the transmission line (a pulse input to input port 103 in FIG. 1) and an output pulse from the transmission line (a pulse output to output port 104 in FIG. 1) in the electromagnetic field simulation. The horizontal axis of FIG. 2(A) is time, and the vertical axis is voltage (however, units are arbitrary). The time width of the pulse is set to approximately 110 ns. FIG. 2(B) shows the S parameters. S 11 is the reflection characteristic of the input side, S 21 represents the passing characteristics from the input side. The horizontal axis of Fig. 2(B) is frequency (unit: Giga Herz: GHz), and the vertical axis is decibels (dB). Because impedance matching is achieved between the tapered tubes 105 and 106 and the thin tube 107, good results were obtained with no significant reflections. In other words, no significant overshoot or undershoot is seen at the rise and fall of the output pulse.

[0043] As an example of a pulse forming circuit using the transmission line 100 of the above embodiment, a configuration may be used in which one end is connected to the secondary side of a transformer (e.g., saturable transformer ST in FIG. 7A) that receives a pulse generated by on-control of a switch (e.g., semiconductor switch SW in FIG. 7A) from a capacitor (e.g., C0 in FIG. 7A) charged by a charger, receives a high-voltage pulse from the secondary side of the transformer, and outputs a pulse to be supplied from the other end to a load (e.g., LOAD in FIG. 7A). As an example of a pulse power supply device, a configuration may be provided that includes a first-stage pulse generating circuit that applies a pulse generated by turning on a switch (e.g., semiconductor switch SW in FIG. 7A) from a capacitor (e.g., C0 in FIG. 7A) charged by a charger to the primary side of a transformer (e.g., saturable transformer ST in FIG. 7A), and a pulse forming line (transmission line 100) having one end connected to the secondary side of the transformer and the other end connected to a load (e.g., LOAD in FIG. 7A), receiving a high-voltage pulse output from the secondary side of the transformer and forming a pulse to be supplied to the load. Note that, for ease of explanation, FIG. 7A in the related art is referred to as an example of a pulse forming circuit and a pulse power supply device, but it goes without saying that the configuration is not limited to that of FIG. 7A and the like.

[0044] In the above embodiment, an example has been described in which a coaxial cylindrical line is used in the pulse forming circuit. However, it goes without saying that the configuration to which the basic principle of the present invention described with reference to FIG. 1 is applied is not limited to a coaxial cylindrical line.

[0045] Fig. 3 is a diagram for explaining an example in which a strip line 300 is used as a parallel plate line constituting a pulse forming circuit of a pulsed power supply. Fig. 3(A) is a schematic plan view of the strip line 300 seen from above, Fig. 3(B) is a schematic cross-sectional view taken along line B-B' in Fig. 3(A), and Fig. 3(C) is a schematic end view taken along line A-A' in Fig. 3(A).

[0046] Referring to FIG. 3(A), a conductor 301 (first conductor) has tapered sections 304, 305 at both ends 306, 307 of a strip line 300, the width of which gradually increases from an intermediate section 308 toward an open end.

[0047] The strip line is configured such that the signal conductor is sandwiched between ground conductors (referred to as "conductor (GND)"). In this embodiment, since the insulating fluid described above is used as the dielectric, the insulating fluid is filled and sealed inside the conductor (GND) 302 (second conductor) made of a straight tube having a rectangular cross section, for example. That is, the side surfaces between the bottom and top surfaces of the opposing conductor (GND) 302 are covered with conductors (GND) 302A and 302B to seal in the insulating fluid and ensure safety. Note that the conductors (GND) 302A and 302B on the side surfaces may be tubes integrated with the conductor (GND) 302 on the bottom and top surfaces, but in FIG. 3, for the sake of explanation, the conductors (GND) 302 on the side surfaces are denoted by different reference numerals 302A and 302B.

[0048] As shown in FIG. 3B and FIG. 3C, the conductor 301 is disposed closer to the bottom side than the top surface of the conductor (GND) 302. That is, the conductor 301 does not have to be disposed at the center height between the top surfaces of the conductors (GND) 302 (as long as impedance matching is ensured). The edges of both sides of the cross section perpendicular to the longitudinal direction of the conductor 301 are preferably rounded (rounded edge processing) to prevent discharge. In addition, the four corners of the inner wall of the conductor (GND) 302 made of a hollow rectangular tube are also preferably rounded (rounded edge processing) to prevent discharge. Such a feature is also a unique feature required for a transmission line that handles high-voltage pulses that need to prevent discharge, but it has not been taken into consideration at all in transmission lines for low-voltage signals that are generally available on the market, or has been treated as an issue that does not need to be taken into consideration.

[0049] In Fig. 3(A), the open ends of the ends 306 and 307 may be covered airtight with an insulating lid or the like, as in Fig. 1. In this case, the open ends of the tapered portions 304 and 305 may be connected to the secondary side of the saturable transformer and the load of the pulse generating circuit shown in Fig. 7(B) and the like, respectively, via an input port and an output port (both not shown) provided on the insulating lid, as in Fig. 1.

[0050] Referring to Figure 3(B), in the cross section at the middle 308 of line B-B' in Figure 3(A), the width of conductor 301 of strip line 300 is w1, the thickness of conductor 301 is t1, and the thickness of dielectric 303 (the distance between the bottom and top surfaces of conductor (GND) 302) is h1.

[0051] Referring to FIG. 3(C), at the end faces of line A-A' in FIG. 3(A) (end faces of ends 306, 307), the thickness of conductor 301 of the strip line is t2 (t2>t1), the thickness of dielectric 303 (the distance between the bottom and top surfaces of conductor (GND) 302) is h2 (h2>h1), and the width of conductor 301 is w2 (w2>w1).

[0052] If the thickness t of the conductor 301 is ignored, the characteristic impedance Z0 per unit length of the strip line is generally calculated by an approximation formula that depends on (w / h) for the width w of the conductor 301 and the thickness h of the dielectric. In this case, if the width w2 of the conductor 301 and the thickness h2 of the dielectric 303 at the end face of the line A-A' in Figure 3(A) are larger than the width w1 and thickness h1 of the intermediate portion 308 between the ends 306 and 307, w2 / h2=w1 / h1 By doing so, the characteristic impedance Z0 of the strip line 300 is kept substantially the same at both ends 306, 307 and at the intermediate portion 308 therebetween, achieving impedance matching. That is, when the width of the conductor 301 is tapered from w1 to w2 at the ends 306, 307, the thickness of the dielectric (the distance between the bottom and top surfaces of the conductor (GND) 302) is also set at the same ratio from h1 to h2.

[0053] Alternatively, based on a numerical calculation result (electromagnetic field simulation result) or an actual measurement value of the characteristic impedance Z0 depending on the thickness of the dielectric of the strip line, for a dielectric 303 of thickness h2, a width w2 of the end face of the conductor 301 that matches the characteristic impedance of the thickness h1 and the width w1 of the conductor 301 may be obtained. In this case, an electromagnetic field simulation may be performed taking into consideration the conductor (GND) 302 made of a straight tube with a rectangular cross section, the conductor 301 placed therein, and the dielectric constant of the dielectric (insulating fluid) filled in the conductor (GND) 302, etc.

[0054] In addition, when using an approximation formula in which the characteristic impedance Z0 of the strip line depends on w / h and t / h, It is also acceptable to set w1 / h1=w2 / h2, t1 / h1=t2 / h2 (w2>w1, h2>h1, t2>t1).

[0055] The thickness h2 of dielectric 303 and the width w2 of conductor 301 (signal pattern) (Figure 3(C)) at the end faces of ends 306, 307 of strip line 300 are both greater than the thickness h1 and the width w1 of conductor 301 (signal pattern) (Figure 3(B)) at intermediate portion 308 of strip line 300, and the area of ​​the end faces of ends 306, 307 defined by conductor 301 and conductor (GND) 302 is greater than the cross section of intermediate portion 308.

[0056] FIG. 4(A) is a diagram showing another example of the strip line of this embodiment. In this example, the strip line 400 has bent portions 410 and 411 that bend the pattern of the conductor 401 at a predetermined angle (180 degrees in FIG. 4(A)) in the intermediate portion 409 between the ends 407 and 408. FIG. 4(B) is a schematic cross-sectional view showing a cross section of the line a-a' in FIG. 4(A). It is needless to say that the number of bent portions 410 and 411 is not limited to two. Although the bending of the conductor 401 affects impedance matching, it is bent quite sharply as shown in FIG. 4(A) in consideration of the frequency to be used (for example, the minimum radius of the bent portions 410 and 411 is about half the wiring interval s of the conductor 401). The width in the a-a' direction in Figure 4(A) requires a width obtained by multiplying the width w1 of conductor 401 by 3 (=number of folds (2) + 1) plus the wiring spacing s of parallel conductors 401 multiplied by 2 (=number of folds).

[0057] The bent conductor 401 is placed in a conductor (GND) 402 made of a straight tube with a rectangular shape. The side surfaces between the bottom and top surfaces of the opposing conductor (GND) 402 are covered with conductors (GND) 402A and 402B to seal in the insulating fluid (dielectric 403) and ensure safety. The conductors (GND) 402A and 402B on the side may be tubes integral with the conductor (GND) 302 on the bottom and top surfaces, but for the sake of explanation in FIG. 4, the conductor (GND) 402 on the side is given different reference numerals 402A and 302B. As with the strip line 300 in FIGS. 3(A) and (B), the end portions 407 and 408 have tapered portions 405 and 406 that are gradually enlarged toward the open end side, and the distance between the bottom surface and the top surface of the conductor (GND) 402 at the end portions 407 and 408 is larger than that at the intermediate portion 409.

[0058] A microstrip line has a ground plane on one side and a signal line on the opposite side across a dielectric substrate, but in this embodiment, since an insulating fluid is used as the dielectric, it has the same configuration as the strip line 300 shown in Fig. 3. That is, the side surfaces between the bottom and top surfaces of the conductor (GND) 302 are covered with conductors (GND) 302A and 302B to seal in the insulating fluid, and the conductor 301 has a tapered portion at the end that gradually widens toward the open end, similar to the strip line 300, and the distance between the bottom and top surfaces of the conductor (GND) 302 at the end is larger than that in the middle portion.

[0059] Fig. 5 is a diagram for explaining an example in which a coplanar line 500 is used as a parallel plate line constituting a pulse forming circuit of a pulsed power supply. Fig. 5(A) is a schematic plan view of the coplanar line as viewed from above. Fig. 5(B) and Fig. 5(C) are schematic diagrams showing a cross section of the coplanar line of Fig. 5(A) other than the end (cross section along line B-B' in Fig. 5(A)) and an end face of the end (cross section along line A-A' in Fig. 5(A)).

[0060] A coplanar line is a transmission line structure in which a signal pattern and a ground conductor are on the same plane, but in this embodiment, an insulating fluid is used as the dielectric, so the insulating fluid is filled inside conductor (GND) 505, which is a straight tube with a rectangular cross section. Both side surfaces between the bottom and top surfaces of conductor (GND) 505 are covered with conductors (GND) 506A and 506B to seal in the insulating fluid and ensure safety.

[0061] In the coplanar line, the signal conductor and the ground conductor on the same plane are composed of a conductor (signal) 501 and conductors 502 and 503 that protrude inward from the inner walls of conductors (GND) 506A and 506B on both sides. The conductors (GND) 505, 506A, and 506B may be composed of an integrally molded tube. The conductors 502 and 503 may be connected to the inner walls of the conductors (GND) 506A and 506B by brazing or the like. As shown in Fig. 5(B) and Fig. 5(C), the edges on both sides perpendicular to the longitudinal direction of the conductor 501 and the edges of the conductors (GND) 502 and 503 arranged opposite the conductor (signal) 501 are preferably rounded to prevent discharge. In addition, the inner wall corners of the conductor (GND) 505 and the conductors (GND) 506A and 506B, which are made of a hollow rectangular tube, are also rounded to prevent discharge.

[0062] 5(A) and (B), the width of conductor (signal) 501 is w1, and the width of gaps 507 and 508 between conductor (signal) 501 and conductors (GND) 502 and 503 is s1. As shown in Figures 5(A) and (C), the width of the end faces of tapered portions 511 and 512 of end portions 513 and 514 is w2, and the width of gaps 509 and 510 between tapered portions 511 and 512 and conductors (GND) 502 and 503 is s2.

[0063] For the characteristic impedance Z0 of coplanar line 500, a model (approximation) that depends on w / (w+2s) and its square can be used with respect to conductor width w and two gaps 2s. Note that characteristic impedance Z0 of coplanar line 500 is proportional to the reciprocal of the square root of the relative dielectric constant, which depends not only on w / (w+2s) but also on thickness h of dielectric 504, but these are ignored for simplicity. In this case, with respect to width w and gap 2s of conductor (signal) 501 at end faces of ends 513 and 514 of coplanar line 500 and at intermediate portion 515 other than ends 513 and 514, w / (w+2s)=r (r is a constant value, except 0 <r<1) In this case, the characteristic impedance Z0 is kept the same at both ends 513, 514 and the middle portion 515 of the coplanar line 500. s = (1-r) × w / (2r) It becomes.

[0064] As shown in Fig. 5(A), at the ends 513 and 514 on both sides of the coplanar line 500, the conductor (signal) 501 forms tapered portions 511 and 512 whose width gradually expands toward the open end side. That is, the width of the tapered portions 511 and 512 expands from w1 on one side (middle portion 515 side) of the ends 513 and 514 to w2 on the other side (open end side). The gaps 509 and 510 between the conductor (signal) 502 and 503 also expand from s1 on one side (middle portion 515 side) of the ends 513 and 514 to s2 on the other side (open end side) in proportion to the width of the conductor (signal) 501. Referring to Figs. 5(B) and (C), the size (width x height) of the end face of the conductor (signal) 501 at the open ends of the ends 513 and 514 is larger than the cross section of the conductor (signal) 501 in the middle portion.

[0065] In Fig. 5(A), the open ends of the ends 513 and 514 may be covered airtight with an insulating lid or the like, as in Fig. 1. In this case, the open ends of the tapered portions 511 and 512 may be connected to the secondary side of the saturable transformer and the load of the pulse generating circuit shown in Fig. 7(B) and the like, respectively, via an input port and an output port (both not shown) provided in the insulating lid, as in Fig. 1.

[0066] Fig. 6 is a diagram for explaining an example of a differential transmission line as another example of the coplanar line shown in Fig. 5. Fig. 6(A) is a schematic plan view, and Fig. 6(B) is a schematic cross-sectional view of line a-a' in Fig. 6(A). Conductor (+ line) 601 and conductor (- line) 602 constituting a differential pair have w1 at intermediate portion 611 between ends 609, 610, and w2 (w2>w1) at the open ends of tapered portions 605-608 of ends 609, 610. The interval s between conductor (+ line) 601 and conductor (- line) 602 is constant at intermediate portion 611, and is expanded at ends 609, 610. The radius R of the bent portion 613 and the bent portion 614 of the conductor (+ line) 601 and the conductor (- line) 602 is set so that the interval between the conductor (- line) 602 facing before and after bending by the bent portion 613 and the interval between the conductor (+ line) 601 facing before and after bending by the bent portion 614 are almost the same as the interval s between the conductor (+ line) 601 and the conductor (- line) 602, but the radius R of the bent portion 613 and the bent portion 614 is appropriately set according to the frequency used, etc. Note that, with respect to the interval s of the differential pair of the conductor (+ line) 601 and the conductor (- line) 602, the interval between the conductor (+ line) 601 facing the inner wall of the side wall 603A of the conductor 603 and the inner wall and the interval between the conductor (- line) 602 and the inner wall may be set to a predetermined distance (for example, 2s or more). In Fig. 6(B), the conductors 601 and 602 are depicted as having flat shapes, but are not limited to this. Like the relationship between a stripline and a coaxial cylindrical line, the conductors 601 and 602 in Fig. 6(B) may be cylindrical with a roughly circular cross section. For example, the feeder line may be embedded in the conductor (GND) 603. The cylindrical conductors 601 and 602 have their ends expanded in diameter toward the open end.

[0067] The transmission lines 300, 400, 500, and 600 described with reference to FIGS. 3 to 6 can also be used as pulse forming lines that shape (form) pulse waveforms in a pulse forming circuit and a pulse power supply, similar to the transmission line 100 in FIG.

[0068] As described above, according to the present embodiment, in a transmission line structure having a pair of electrodes (conductors) constituting a coaxial cylindrical line or a parallel plate line, a transmission line structure having the pair of electrodes (conductors) can be provided that allows a device to be further miniaturized as compared to related techniques such as Patent Document 3, by mainly matching the impedance of the end portion with that of the other portions while making the opening larger compared to the other portions.

[0069] Moreover, by using the transmission line structure of the above-described embodiment as a circuit, it is possible to provide a circuit that allows the device to be further miniaturized.

[0070] Although the transmission line structure having a pair of electrodes (conductors) constituting a coaxial cylindrical line or a parallel plate line has been described as an example, the present invention is not limited to this. For example, the effect of the present invention can be obtained also in a transmission line structure consisting of a set of conductors including a positive conductor, a negative conductor, and a ground conductor for transmitting pulses of both polarities. Alternatively, by applying the present invention to a double coaxial line (Blumlein line) of a pulse power supply as shown in Figure 7(B), the transmission line structure can be made compact, and it is of course possible to further miniaturize a pulse forming circuit and a pulse power supply device equipped with the transmission line structure.

[0071] The disclosures of the above Patent Documents 1-3 and Non-Patent Document 1 are incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure of the present invention (including the scope of the claims), and further based on the basic technical ideas. Furthermore, various combinations and selections of the various disclosed elements (including each element of each claim, each element of each example, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. In other words, the present invention naturally includes various modifications and alterations that a person skilled in the art would be able to make in accordance with the entire disclosure including the scope of the claims and the technical ideas. [Explanation of symbols]

[0072] 100 Transmission Line 101 Outer conductor (second conductor) 102 Inner conductor (first conductor) 103 Small diameter tube 103 Input Port 104 Output Ports 105, 106 Tapered tube 107 Small diameter tube 108, 109 Inner conductor 110, 111 Insulating cover 112, 113 Edge (triple point) 114, 115 End 116, 117 Bending part 300 Stripline (transmission line) 301 Conductor (signal line) 302, 302A, 302B Conductor (GND) 303 Dielectrics (insulating fluids) 304, 305 Tapered section 306, 307 Ends 308 Middle Section 400 Stripline (transmission line) 401 Conductor (signal line) 402, 402A, 402B Conductor (GND) 403 Dielectrics (insulating fluids) 405, 406 Tapered section 407, 408 End 409 Middle Section 410, 411 Bending part 500 Coplanar line (transmission line) 501 Conductor (signal) 502, 503, 506A, 506B Conductor (GND) 504 Dielectrics (insulating fluids) 507, 508, 509, 510 Gap 511, 512 Tapered section 513, 514 End 515 Middle 601 Conductor (+ line) 602 Conductor (-line) 603, 603A, 603B Conductor (GND) 604 Dielectrics (insulating fluids) 605, 606, 607, 608 Tapered section 609, 610 End 611 Middle section 612, 613, 614, 615 Bending section

Claims

1. A transmission line used for a pulse wave forming type, the transmission line having first and second conductors constituting a coaxial cylindrical line or a parallel plate line, the first conductor is disposed in a tube of the second conductor and is filled with an insulating fluid, and the inside of the tube other than the end of the transmission line and the first conductor are covered with a single insulating fluid; A transmission line in which the impedance of the end of the transmission line is matched with other ends, and a cross section of the end is expanded to prevent dielectric breakdown when a high voltage pulse is applied, thereby reducing the diameter of the transmission line other than the end.

2. the first and second conductors extend from one end to the other end in a longitudinal direction of the transmission line while being spaced apart from each other; 2. The transmission line according to claim 1, wherein at least one of the first and second conductors has a width or cross section in a direction perpendicular to the longitudinal direction of the transmission line at end faces of the end portions on both sides in the longitudinal direction of the transmission line that is larger than a width or cross section at a location other than the end faces of the end portions and at an intermediate portion between the end portions on both sides, and the transmission line is impedance-matched between the end portions on both sides in the longitudinal direction and the intermediate portion.

3. the second conductor constitutes an outer conductor of the coaxial cylindrical line; the first conductor constitutes an inner conductor disposed coaxially with the outer conductor within a cylindrical tube of the outer conductor; the outer conductor, at the end portion, constitutes a tapered tube whose diameter gradually increases from a side facing an end face of the end portion toward the end face, 3. The transmission line according to claim 1, wherein the inner conductor has a diameter gradually increasing from a side of the end portion facing the end face toward the end face in accordance with a shape of the outer conductor.

4. 4. The transmission line according to claim 3, wherein a ratio of a radius of the inner conductor to an inside diameter of the outer conductor is the same at the end and at a location other than the end of the transmission line.

5. 5. The transmission line according to claim 3, wherein at the end, the internal conductor has a hollow cylindrical shape whose diameter gradually increases from a side facing an end face of the end toward the end face, and the cylindrical side has one or more through holes of a predetermined size.

6. the first conductor and the second conductor constitute the parallel plate line; At the end portion, the first conductor has a tapered shape in which its width gradually increases from a side facing an end face of the end portion toward the end face, 3. The transmission line according to claim 1, wherein at the end, a distance between the first conductor and the second conductor gradually increases from a side facing an end face of the end toward the end face.

7. 7. The transmission line of claim 6, wherein a ratio of the width of the first conductor to the spacing between the first conductor and the second conductor is the same at the end and at any point other than the end of the transmission line.

8. 8. The transmission line according to claim 6, wherein the first conductor has a plate-like cross-sectional shape perpendicular to the longitudinal direction of the transmission line, and both edges of the first conductor are rounded to remove corners as a measure to prevent discharge.

9. 8. The transmission line according to claim 6, wherein the first conductor has a circular cross section perpendicular to a longitudinal direction of the transmission line.

10. 10. The transmission line according to claim 6, wherein the second conductor is a tube having a hollow rectangular cross section perpendicular to a longitudinal direction of the transmission line, and the four corners of the inner wall of the cross section of the tube are rounded as a measure to prevent discharge.

11. 11. The transmission line according to claim 6, wherein the first conductor is made up of two conductors forming a differential balanced line.

12. 12. The transmission line according to claim 1, wherein the insulating fluid is a thermoplastic resin that is in a liquid state when filled.

13. 13. The transmission line according to claim 1, wherein the high voltage pulse is 100 kV (kilovolt) or more.

14. 14. A pulse forming circuit comprising the transmission line according to claim 1 as a pulse forming line having one end connected to a secondary side of a transformer which receives at its primary side a pulse generated by on-control of a switch from a capacitor charged by a charger and has the other end connected to a load, receiving a pulse output from the secondary side of the transformer and outputting a pulse to be supplied from the other end to the load.

15. A first-stage pulse generating circuit applies a pulse generated by switching on the capacitor charged by the charger to the primary side of the transformer; a pulse forming line having one end connected to the secondary side of the transformer and the other end connected to a load, receiving a pulse output from the secondary side of the transformer and forming a pulse to be supplied to the load; Equipped with A pulse power supply comprising the transmission line according to claim 1 as said pulse forming line.

Images