Transmission line

Abstract

Transmission line (20), comprising: - a plurality of parallel arranged electrical conductors (23a), each with a central highly conductive wire (21), each with an inner conductive layer (22) which is formed around the central highly conductive wire (21), and with an electrical insulation layer (23) surrounding the inner conductive layer (22), - an electrical insulator (24) surrounding the electrical conductors (23a), - an outer conductive layer (25) surrounding the electrical insulator (24), - an electrical shield (26) surrounding the outer conductive layer (25), wherein the inner conductive layer (22) and / or the outer conductive layer (25) comprises a material whose conduction losses are frequency-dependent.

Description

[0001] The invention relates to a transmission line. The invention also relates to a high-voltage transmission chain.

[0002] Accelerator systems are used to generate high-energy X-ray photons in the range between 1 MeV and 25 MeV, as used, for example, in materials testing or radiation therapy. Such an accelerator system comprises a radio-frequency power source consisting of a magnetron, a modulator, and a beam head. The requirement is that the modulator and the beam head must be spatially separated from the RF source (e.g., a magnetron). These requirements are based on mechanical reasons (e.g., the system's center of gravity), but also on radiation protection reasons (e.g., protecting the electronics from high-energy photons and / or neutrons). RF sources include oscillators (e.g., a magnetron) and amplifiers (e.g., a klystron), which are operated in pulsed mode. A transmission line (without attenuation) between the modulator and the RF source (abbreviation for radio frequency source, e.g.,However, a magnetron leads to undesirable feedback effects if the impedance match between the modulator, cable, and RF source (especially a magnetron) is not ensured. Reflections can cause standing waves (wavelengths in the range of several tens of centimeters) to form on the transmission line. These can disrupt the performance of the system generating high-frequency power and, in extreme cases, destroy the cable due to local field peaks. An arrangement of a high-voltage transmission chain for transmitting power pulses with a magnetron is described in . Fig. 1 shown.

[0003] The feedback effect can be compensated for by attaching ferrite filters and absorbers to the ends of a transmission line to suppress high-frequency coupling into the line. One disadvantage is that the ferrites can result in a mismatched impedance between the line and the magnetron.

[0004] The feedback effect can also be compensated by additional circuitry with RC elements (complex resistance elements) to absorb the high-frequency components. A disadvantage is that the RC elements are spatially discrete, which reduces the effectiveness of the damping in terms of frequency filtering. In addition, the filters influence the voltage rise time of the system, which can also have a detrimental effect.

[0005] The feedback effect can also be compensated by switching on the modulator for a longer period of time (by extending the voltage rise time) to reduce the frequency spectrum of the pulse and thus reduce the high-frequency spectrum of reflections occurring during the pulse. A disadvantage of this approach is that a minimum rise rate is necessary for the magnetron to function, and thus the voltage rise time cannot be extended indefinitely.

[0006] The object is therefore to provide a transmission line which can be connected in particular between a modulator and an RF source, which at least mitigates the disadvantages described above.

[0007] This object is achieved by a transmission line according to patent claim 1 and a high-voltage transmission chain according to patent claim 14.

[0008] The transmission line according to the invention comprises a plurality of parallel electrical conductors. An "electrical conductor" is understood to be a conductive element that conducts electrical current. The structure of the conductive element is adapted to the type of current or electrical signal to be conducted. Several of these conductors, together with additional components arranged around the conductors, form the transmission line.

[0009] The electrical conductors, arranged parallel to one another, are each formed with a central, highly conductive core, an inner conductive layer formed around the core, and an electrical insulation layer surrounding the inner conductive layer. A highly conductive core is to be understood as a line-like solid body made of an electrically highly conductive material, preferably copper. The inner conductive layer preferably comprises a material that is significantly less electrically conductive than the material of the highly conductive core surrounded by the inner conductive layer. The inner conductive layer serves to suppress electrical field peaks, for example in the case of broken copper strands. According to the invention, the inner conductive layer serves to dampen higher alternating current frequencies to which the transmission line is subjected.The electrical insulation layer surrounding the inner conductive layer is designed to function as high-voltage insulation between the parallel electrical conductors. The specific conductivity of the conductive layer is in the range of 2 S / m - 100 S / m ("S" stands for Siemens).

[0010] The transmission line according to the invention also comprises an electrical insulator surrounding the electrical conductors and an outer conductive layer surrounding the electrical insulator. The outer conductive layer preferably also has a reduced electrical conductivity compared to the central, highly conductive core. The electrical insulator serves as high-voltage insulation to the outside, i.e., to the outer conductive layer. The outer conductive layer serves to dampen the higher alternating current frequencies at which the transmission line was operated. It also serves to suppress electric field peaks, for example, in the case of broken copper strands.

[0011] Furthermore, the transmission line according to the invention comprises an electrical shield surrounding the outer conductive layer.

[0012] The inner conductive layer and / or the outer conductive layer comprises a material whose conduction losses are frequency-dependent. Conduction loss is understood to be a loss of electrical power of the transmitted electrical current or electrical signal. For frequency-dependent continuous attenuation, the inner conductive layer preferably completely surrounds the respective highly conductive wire in the longitudinal and circumferential directions and / or the outer conductive layer completely surrounds the electrical insulator in the longitudinal and circumferential directions. The material used for the inner conductive layer and / or the outer conductive layer is preferably a mixture of an electrically insulating material and a material that exhibits a strong interaction with electromagnetic waves and a frequency-dependent filtering effect.Such a material is preferably electrically conductive or has magnetic, preferably soft magnetic, particularly preferably ferrimagnetic properties, for interaction with electromagnetic waves at high frequencies.

[0013] According to the invention, a delocalized absorption of high-frequency components occurs due to the frequency-dependent continuous attenuation. Thus, the transmission line according to the invention fulfills the properties of a low-pass filter over its entire length. Thus, a continuous low-pass filter effective across all frequencies or a broad frequency range is realized.

[0014] The high-voltage transmission chain according to the invention comprises a modulator, a transmission line according to the invention, and a high-frequency generation unit. The transmission line according to the invention transmits a pulsed signal from the modulator to the high-frequency generation unit. The high-voltage transmission chain according to the invention shares the advantages of the transmission line according to the invention.

[0015] In a method for manufacturing a transmission line, a plurality of electrical conductors are arranged in parallel. Each electrical conductor is formed with a central, highly conductive core, an inner conductive layer formed around the core, and an electrical insulation layer surrounding the inner conductive layer.

[0016] The electrical conductors are thus surrounded by an inner conductive layer and then an electrical insulator. The electrical insulator is surrounded by an outer conductive layer. The outer conductive layer is surrounded by an electrical shield. The inner conductive layer and / or the outer conductive layer are coated with a material whose power losses are frequency-dependent. The inner conductive layer is preferably designed such that it completely surrounds the respective highly conductive wire in both the longitudinal and circumferential directions.

[0017] Preferably, the electrical conductors are arranged symmetrically so that they each have an electrical capacitance of the same value relative to the outer conductive layer. The method for producing a transmission line shares the advantages of the transmission line according to the invention. If the electrical conductors are arranged symmetrically, a capacitively coupled differential voltage between the inner conductors, which are used, for example, for heating and connecting a cathode of an RF source, is reduced. In this way, interference caused by a standing wave between capacitively coupled components, such as the heater and the cathode, can be avoided or significantly reduced.

[0018] The dependent claims and the following description each contain particularly advantageous embodiments and developments of the invention. In particular, the claims of one claim category can also be developed analogously to the dependent claims of another claim category. Furthermore, within the scope of the invention, the various features of different embodiments and claims can also be combined to form new embodiments.

[0019] In a preferred variant of the transmission line according to the invention, the inner and / or outer conductive layer is configured as a low-pass filter to attenuate higher frequencies. Interference frequencies, particularly in the range from 1 GHz to 9 GHz, can be advantageously attenuated. The thicker the inner and / or outer conductive layer, the lower the frequencies attenuated.

[0020] To absorb higher frequencies, the frequency-dependent absorbing material, whose conduction losses are frequency-dependent, preferably has a complex permittivity or a complex dielectric conductivity. In a dielectric with a complex permittivity, polarization fields form when alternating fields occur, but these fields lag behind the applied external field magnitude by a certain phase angle. With increasing frequency, the phase shift increases, leading to the generation of heat energy and the damping of the alternating fields.

[0021] Alternatively or additionally, the frequency-dependent absorbing material, whose conduction losses are frequency-dependent, can also exhibit a complex relative magnetic permeability, i.e., a complex magnetic conductivity. In this variant, a reduction of electromagnetic fields occurs by damping alternating magnetic fields.

[0022] In a preferred variant of the transmission line according to the invention, the electrical conductors are arranged symmetrically so that they each have an electrical capacitance of the same value with respect to the outer conductive layer. If the transmission line is therefore constructed symmetrically, the two inner conductors or electrical conductors of the transmission line to the shield have an identical capacitance and inductance. This reduces a capacitively coupled differential voltage between the two inner conductors (cores), which are used, for example, for heating and connecting a cathode of an RF source. The symmetrical structure advantageously allows the absorption of the high-frequency components to be delocalized. The symmetrical transmission line according to the invention therefore fulfills the properties of a spatially distributed low-pass filter (in contrast to conventional solutions) over the entire length of the transmission line.In contrast to the conventional discrete solutions described above, no spatially localized impedance jump occurs.

[0023] In a preferred embodiment of the transmission line according to the invention, the majority of the parallel conductors have an even value. Advantageously, the even number of conductors allows a symmetrical electric field to be formed toward the electrical shield.

[0024] In the simplest case, the majority of the conductors arranged parallel to each other have the value 2. This variant is particularly simple and can be implemented with little resource expenditure due to the minimal number of conductors used.

[0025] Preferably, the inner and / or outer conductive layer is designed to suppress electric field peaks, preferably in the event of a defect in the conductor, and to absorb high-frequency components. This advantageously prevents additional damage due to defects and the resulting field peaks.

[0026] In a preferred variant of the transmission line according to the invention, the inner and outer conductive layers comprise a mixture of rubber and carbon. Rubber is a good insulator. Carbon in the form of graphite exhibits relatively good electrical conductivity and ensures that the two conductive layers maintain residual conductivity, resulting in absorption by eddy currents and losses due to polarization reversal, thus damping higher frequency components.

[0027] Alternatively, rubber and ferritic materials, e.g. black iron oxide, can be used for the inner and outer conductive layer, whereby the metal particles generate losses due to the changing magnetic field and thus dampen higher frequency components.

[0028] The central, highly conductive cores of the transmission line according to the invention preferably comprise copper. Copper has high electrical conductivity.

[0029] It is also preferred that the electrical shield of the transmission line according to the invention comprises a copper braid. A copper braid is an excellent conductor for conducting high-frequency electrical currents and for shielding electric fields.

[0030] The invention is explained in more detail below with reference to exemplary embodiments in the accompanying figures. They show: Fig. 1 a schematic representation of a high-voltage transmission chain with conventional transmission lines, Fig. 2 a cross-sectional view of a conventional transmission line, Fig. 3 a schematic representation of a capacitive connection between the inner conductors and the shield of a conventional transmission line, Fig. 4 a cross-sectional view of a transmission line according to an embodiment of the invention, Fig. 5 a schematic representation of a capacitive connection between the inner conductors and the shield of the Fig. 4 shown transmission line, Fig. 6 diagrams illustrating the attenuation of higher frequencies as a function of the thickness of the conductive layers, Fig. 7 is a flow chart illustrating a method for manufacturing a transmission line, Fig. 8 is a block diagram illustrating a high-voltage transmission chain according to an embodiment of the invention.

[0031] In Fig. Figure 1 shows a schematic representation of a high-voltage transmission chain 10 with conventional transmission lines. The high-voltage transmission chain 10 has a modulator 2. Part of the modulator 2 is also a step-down converter, with which, for example, a pulse with a duration of 5 µs and a current of 120 A is generated. The high-voltage transmission chain 10 also includes a magnetron 3, which is designed to generate electromagnetic waves in the microwave range. Fig. 1 shows a front view of a connector 1a of a transmission line 1. The front view of the connector 1a shows insulated conductors 5, 6, 7 and a non-insulated conductor 4.

[0032] In Fig. Figure 2 shows a cross-sectional view of a conventional transmission line 1. The transmission line 1 comprises three insulated conductors 5, 6, 7 with insulated cores 5a, 6a, 7a, and three uninsulated cores 4, each of which marks the corners of a triangle. The two triangles are arranged opposite each other. The insulated cores 5a, 6a, 7a of the conductors 5, 6, 7 are surrounded by insulation layers 5b, 6b, 7b.

[0033] An inner conductive layer 8 made of rubber with carbon is arranged around the conductors 4, 5, 6, and 7. High-voltage insulation 9 is formed around the inner conductive layer 8. An outer conductive layer 11 made of rubber with carbon is arranged around the high-voltage insulation 9. The outer sheath is formed by a shield 12 made of a copper braid. The shield 12 is covered against the environment with a plastic layer (not shown), which acts as an outer insulation layer.

[0034] In Fig. Figure 3 shows a schematic representation of the capacitive connection between the inner conductors and the shield of a conventional transmission line 1. The inner conductors 4, 5, 6, 7 carry the voltage pulse. They are protected from the voltage pulse by a capacitor C k short-circuited (see picture below in Fig. 3). The arrows symbolize the pulse current distribution when the pulse is switched on, which is asymmetrical. The heating energy and the pulse energy are transferred between the inner conductors 5, 6, 7 and the three uninsulated conductors 4. The heating energy is transferred in push-pull mode (from the insulated conductors 7, 6 to the insulated conductor 5 and the uninsulated wires or conductors 4), and the pulse energy is transferred in common mode.

[0035] In Fig. 4 shows a cross-sectional view of a transmission line 20 according to an embodiment of the invention. Fig. The transmission line 20 shown in Figure 4 comprises two electrical conductors 23a arranged symmetrically relative to an outer electrical shield 26. The conductors comprise an inner, highly electrically conductive core 21, a conductive layer 22 formed around the highly electrically conductive core 21 and comprising a conductive layer and / or a ferrite layer. An insulating layer 23 or an electrical insulator 24 is formed around the conductive layer 22, forming HV insulation between the conductors and also relative to an outer conductive layer 25 and an outer electrical shield 26 formed therearound (optionally insulated from the outside by an outer insulating layer, for example, a plastic sheath).

[0036] In Fig. 5 is a schematic representation of the capacitive connection between the inner conductors 23a and the shield 26 of the Fig. 4. Due to a symmetrical arrangement, both conductors have the same conduction capacitance to the outer electrical shield 26. The same current components at the moment of switching on of the pulse current are represented by the arrows along the conductors 23a in the same direction.

[0037] In Fig. 6 shows diagrams 60 illustrating the attenuation S21 of higher frequencies or the transmission in a transmission line according to an exemplary embodiment as a function of the thickness of the conductive layers. Attenuation S21 is shown in decibels (dB) for thicknesses from 0.2 mm to 1 mm as a function of the frequency in MHz. The diagram on the left shows the transmission in common-mode mode, and the diagram on the right shows it in differential mode. The values ​​refer to a fixed simulated length of the transmission line. It can be seen that thicker conductive layers have a stronger attenuation effect than thinner conductive layers.

[0038] In Fig. 7 is a flowchart 700 illustrating a method for manufacturing a transmission line 20.

[0039] In step 7.I, a plurality of electrical conductors 23a are formed, each having a central highly conductive wire 21, an inner conductive layer 22 formed around the highly conductive wire 21, and an electrical insulation layer 23 surrounding the inner conductive layer 22.

[0040] The electrical conductors 23a are surrounded by an electrical insulator 24 in step 7.II.

[0041] In step 7.III, the electrical insulator 24 is surrounded by an outer conductive layer 25.

[0042] In step 7.IV, the outer conductive layer 25 is surrounded by an outer electrical shield 26. The outer conductive layer 25 and the inner conductive layer 22 are formed from a material whose conduction losses are frequency-dependent.

[0043] In Fig.Figure 8 shows a block diagram illustrating a high-voltage transmission chain 10a according to an embodiment of the invention. The high-voltage transmission chain 10a comprises a modulator 2 and a magnetron 3, as well as a transmission line 20 connected between the modulator 2 and the magnetron 3 according to an embodiment of the invention.

[0044] Finally, it is pointed out once again that the devices described above are merely preferred embodiments of the invention and that the invention can be varied by a person skilled in the art without departing from the scope of the invention, insofar as it is defined by the claims. For the sake of completeness, it is also pointed out that the use of the indefinite articles “a” or “an” does not exclude the possibility that the features in question may be present in multiple copies. Likewise, the term “unit” does not exclude the possibility that it consists of several components, which may also be spatially distributed. Regardless of the grammatical gender of a particular term, this includes persons with male, female or other gender identities.

Claims

[1] Transmission line (20), comprising: - a plurality of parallel arranged electrical conductors (23a), each with a central highly conductive wire (21), each with an inner conductive layer (22) which is formed around the central highly conductive wire (21), and with an electrical insulation layer (23) surrounding the inner conductive layer (22), - an electrical insulator (24) surrounding the electrical conductors (23a), - an outer conductive layer (25) surrounding the electrical insulator (24), - an electrical shield (26) surrounding the outer conductive layer (25), wherein the inner conductive layer (22) and / or the outer conductive layer (25) comprises a material whose conduction losses are frequency-dependent. [2] Transmission line according to claim 1, wherein the inner conductive layer (22) and / or the outer conductive layer (25) has a lower electrical conductivity compared to the central highly conductive wire (21). [3] Transmission line according to one of the preceding claims, wherein the inner conductive layer (22) comprises a low-pass function to attenuate higher frequency components and / or the outer conductive layer (25) comprises a low-pass function to attenuate higher frequency components. [4] Transmission line according to one of the preceding claims, wherein the material whose line losses are frequency dependent has a complex permittivity. [5] Transmission line according to one of the preceding claims, wherein the material whose conduction losses are frequency dependent has a complex relative magnetic permeability. [6] Transmission line according to one of the preceding claims, wherein the electrical conductors (23a) are arranged symmetrically such that they each have an electrical capacitance of the same value with respect to the outer conductive layer (25). [7] Transmission line according to one of the preceding claims, wherein the plurality of parallel arranged electrical conductors (23a) has an even value. [8] Transmission line according to one of the preceding claims, wherein the plurality of electrical conductors (23a) arranged parallel to one another has the value 2. [9] Transmission line according to one of the preceding claims, wherein the inner conductive layer (22) is designed to suppress electric field peaks, preferably in the event of a defect in the electrical conductors (23a). [10] Transmission line according to one of the preceding claims, wherein the inner conductive layer (22) comprises a mixture of rubber and carbon. [11] Transmission line according to one of the preceding claims, wherein the central highly conductive wires (21) comprise copper. [12] Transmission line according to one of the preceding claims, wherein the outer conductive layer (25) comprises a mixture of rubber and carbon. [13] Transmission line according to one of the preceding claims, wherein the electrical shield (26) comprises a copper braid. [14] High-voltage transmission chain (10), comprising: - a modulator (2), - a high-frequency generation unit (3) - a transmission line (20) according to one of the preceding claims between the modulator (2) and the high-frequency generation unit (3).

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