Non-relativistic beam transverse coupling impedance measurement method

Abstract

The invention belongs to the crossing field of accelerator physics and microwave measurement, and relates to a non-relativistic beam transverse coupling impedance measurement method based on an off-axis helix slow wave structure. The method comprises the following steps: inserting an off-axis helix copper wire into a to-be-tested ceramic vacuum box, guiding and fixing the off-axis helix copper wire through a PVC skeleton, finely adjusting the position of the off-axis helix copper wire through a horizontal and vertical displacement adjusting assembly, and simulating non-relativistic beam propagation; applying excitation sweep frequency pulse signals to the two ends of the copper wire through a vector network analyzer, obtaining microwave transmission parameters, and calculating transverse coupling impedance according to the microwave transmission parameters; according to the invention, traditional limitation is broken through, non-relativistic beam high-precision measurement is realized, low-frequency impedance frequency-dependent characteristics can be analyzed, extremely low frequency is covered, the signal-to-noise ratio is high, single conductor measurement and spiral line configuration slow wave structure technologies are protected, the device is simplified, and the cost is reduced.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of accelerator physics and microwave measurement technology, specifically relating to a non-relativistic beam transverse coupling impedance measurement method based on an off-axis spiral slow wave structure. Background Technology

[0002] Accurate measurement of beam coupling impedance is a crucial method for evaluating the performance of acceleration vacuum components in modern accelerators. In accelerator technology, the transverse coupling impedance of the beam directly affects beam stability and transmission efficiency. Therefore, accurate measurement of transverse coupling impedance is of great significance for optimizing accelerator design and improving beam quality.

[0003] Currently, the industry commonly uses the double-parallel-line method for transverse impedance measurement. This method involves inserting a pair of parallel transmission lines into the vacuum component under test and applying reverse excitation signals. A vector network analyzer is then used to measure frequency domain reflection and transmission parameters and calculate the impedance. However, the double-parallel-line method has significant limitations: First, the electromagnetic field generated by the vector network analyzer can only propagate at the speed of light within the vacuum chamber. Therefore, theoretically, it can only measure scenarios where the beam velocity is the speed of light, i.e., the beam velocity factor β = v / c = 1. But in actual accelerators, the velocity of charged particles is usually less than the speed of light, i.e., the velocity factor β < 1. Therefore, the double-parallel-line method cannot be directly applied to the transverse coupling impedance measurement of non-relativistic beams.

[0004] Secondly, when the measurement frequency drops below 10MHz, the electromagnetic coupling efficiency between the two lines decreases sharply, and the transmitted signal amplitude is completely submerged by the instrument's background noise, making it impossible to obtain a valid signal. This problem is particularly prominent in the extremely low frequency domain, severely limiting the application range of the double parallel line method.

[0005] To address the aforementioned issues, international efforts have focused on generating slow-wave electromagnetic field structures to simulate the propagation of non-relativistic beams in vacuum components and achieve high-precision lateral coupling impedance measurements. However, traditional methods face technical bottlenecks in realizing slow-wave structures, making it difficult to meet the demands of high-precision measurements. Summary of the Invention

[0006] To address the aforementioned issues, this invention aims to provide a method for measuring the transverse coupling impedance of a non-relativistic beam based on an off-axis spiral slow-wave structure. This method focuses on the measurement of the transverse coupling impedance of a non-relativistic beam (velocity factor β < 1), overcoming the technical limitations of traditional measurement methods in non-relativistic scenarios and low-frequency bands, and providing an innovative solution for the performance evaluation of accelerator vacuum components.

[0007] The technical solution adopted by this invention to solve the technical problem is: a method for measuring the transverse coupling impedance of a non-relativistic beam, comprising the following steps: An off-axis spiral copper wire is inserted into the ceramic vacuum chamber to be tested; The propagation speed of electromagnetic waves in the component under test is reduced by using spiral copper wires to simulate the propagation of non-relativistic beams. An excitation sweep pulse signal is applied to one end of the copper wire by a vector network analyzer, and microwave transmission parameters are obtained at the other end by the vector network analyzer. The transverse coupling impedance of the non-relativistic beam is calculated based on the obtained microwave transmission parameters.

[0008] The spiral copper wire is guided and fixed by a PVC skeleton, and its position in the vacuum box is adjusted by horizontal displacement adjustment components and vertical displacement adjustment components.

[0009] The horizontal displacement adjustment component and the vertical displacement adjustment component are used to adjust the horizontal and vertical positions of the helix, respectively, to excite and acquire electromagnetic field signals of the helix in different positions.

[0010] The vector network analyzer is connected to a spiral copper wire via a cable and adapter to send and receive test signals.

[0011] The measurement method also includes a step of calibrating the vector network analyzer to ensure measurement accuracy.

[0012] The measurement method measures the transmission parameter S by measuring the position of the helix at its horizontal center and a set of horizontal off-axis positions. 21 To calculate the transverse coupling impedance of the non-relativistic beam.

[0013] The scanning step size for the horizontal off-axis position is 10mm, and the maximum off-axis distance is 40mm, in order to reduce measurement errors and prevent accidental damage to measurement data.

[0014] The measurement method further includes replacing the ceramic vacuum box under test with a stainless steel vacuum box of the same cross-section and length, and measuring the transmission parameter S at the same off-axis position. 21 This is to deduct systematic errors from transmission lines and measurements.

[0015] The measurement method measures the transverse coupling impedance of a non-relativistic beam with different velocity factors β by changing the helix with different pitches, where the velocity factor β = L0 / L, L is the length of the vacuum cell, and L is the length of the helix.

[0016] The measurement method utilizes a spiral structure to simulate the propagation speed of a non-relativistic beam in a circular vacuum box, excites real induced electromagnetic waves, and achieves non-relativistic transverse impedance measurement through fine adjustment of the position of the spiral cross-section, covering an extremely low frequency range and maintaining a high signal-to-noise ratio within the ~10kHz measurement range.

[0017] This invention proposes a method for measuring the transverse coupling impedance of non-relativistic beams, which effectively solves the technical difficulties of the traditional double-parallel-line method in non-relativistic beam measurements and has significant beneficial effects: This invention simulates the propagation of a non-relativistic beam by inserting an off-axis helical copper wire, which reduces the propagation speed of electromagnetic waves in the component under test. This innovative design overcomes the limitation of traditional methods that can only measure beams at the speed of light, and achieves high-precision measurement of the lateral coupling impedance of non-relativistic beams.

[0018] This invention achieves slow-wave propagation of electromagnetic waves through a meticulously designed helical structure, thereby accurately resolving the impedance frequency-varying characteristics of low-frequency non-relativistic beams. This technological innovation significantly improves measurement accuracy and provides reliable data support for accelerator design.

[0019] This invention covers an extremely low frequency range (~10kHz) while maintaining a high signal-to-noise ratio within this band. This advantage enables the invention to perform exceptionally well in impedance measurements at extremely low frequencies, effectively solving the problem of low signal-to-noise ratio in traditional methods at low frequencies.

[0020] This invention uses horizontal and vertical displacement adjustment components to finely adjust the lateral position of a helix, thereby exciting and acquiring electromagnetic field signals of the helix in different positions. This design adapts to a wide range of measurement needs, ensuring high-precision measurement results under various configurations.

[0021] This invention protects the single-wire non-relativistic transverse impedance measurement technology, which realizes the measurement of the transverse coupling impedance of non-relativistic beams through a single off-axis spiral wire, simplifying the measurement device and reducing costs.

[0022] This invention protects the slow-wave beam structure technology with a helical configuration. By simulating the propagation speed of a non-relativistic beam in a circular vacuum box through the helical structure, it excites real induced electromagnetic waves, thereby achieving accurate calculation of the beam coupling impedance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the mechanical cross-sectional structure of the core area of ​​the measuring device in this invention.

[0024] Figure 2 This is a side view of the core area of ​​the measuring device in this invention.

[0025] Figure 3 Assembly drawing of the measuring device of the present invention; Figure 4 This is a schematic diagram of the device of the present invention; Figure 5 This is a schematic diagram of the helical coil assembly structure in this invention; Figure 6 yes Figure 5 A magnified view of the middle left side; Figure 7 This is a schematic diagram of the measurement process principle of the present invention; Figure 8 This is a schematic diagram of the structure used to adjust the position of the spiral in this invention.

[0026] In the figure, 1-Ceramic vacuum box test piece, 2-Cover plate, 3-Fixing component, 4-PVC frame, 5-Helix, 6-Positioning pin, 7-Vertical displacement adjustment component, 8-Horizontal displacement adjustment component, 9-Copper wire, 10-Adapter, 11-Vector network analyzer, 12-Cable, 13-Coil frame pull block, 14-Pull rod. Detailed Implementation

[0027] This invention proposes a method for measuring the lateral coupling impedance of non-relativistic beams, aiming to overcome the technical bottleneck of the traditional double-parallel-line method in measuring the lateral coupling impedance of non-relativistic beams, and providing a reliable solution for high-precision lateral coupling impedance measurement of non-relativistic beams. The invention will be described in detail below with reference to the accompanying drawings and specific embodiments: like Figure 1 As shown, the core area of ​​the measuring device in this invention uses the ceramic vacuum box (test object 1) as its core to maintain the vacuum environment required for beam movement. The cover plate 2 maintains the vacuum area and positioning base, determining the measurement accuracy. Fixing screws 3 secure the vacuum box 1 and cover plate 2. A PVC frame 4 guides and fixes the spiral 5. Positioning pins 6 ensure that the cover plate 2 and spiral 5 are in an ideal plane. A vertical displacement adjustment assembly 7 adjusts the spiral 5 to its vertical center, and a horizontal displacement adjustment assembly 8 adjusts its horizontal position to excite and acquire electromagnetic field signals. Figure 3 As shown, the ceramic vacuum box test piece 1 is the core, and the cover plate 2, fixing screws 3, PVC frame 4, spiral wire 5, positioning pin 6, vertical and horizontal displacement adjustment components 7 and 8, copper wire 9 and other components are assembled according to the design requirements to ensure the stability and accuracy of the measuring device. Figure 4 The signal transmission path and component connections are illustrated. Adapter 10 connects to spiral wire 5, allowing adjustment of the signal input / output interface to accommodate different measurement cable ports. Vector network analyzer 11 connects to adapter 10 via cable 12, sending test signals and receiving feedback signals to calculate the beam current transverse coupling impedance. Figure 5 The diagram shows the structure where the spiral wire 5 is wound on a PVC frame 4, with copper wire 9 connected to the spiral wire 5 for feeding and receiving signals. The coil frame pull block 13 and pull rod 14 secure and tighten the spiral wire 5. Figure 6 The complete electrical connection between the copper wire 9 and the spiral wire 5, as well as the insulation design between the copper wire 9 and the surrounding metal, are shown in detail to ensure the purity and accuracy of signal transmission. Figure 7This demonstrates the steps for measuring the transverse coupling impedance of a non-relativistic beam based on an off-axis helical slow-wave structure: S1. Selecting the helical line and assembling the device: Choose a suitable helical line according to the measurement requirements and assemble the measurement device; S2. With the helical line at the center, measure the parameters: Adjust the helical line to the horizontal center and measure the reflection and transmission parameters S. 21 S3. Scan and measure the horizontal offset axis: Change the position of the horizontal offset axis of the spiral in 10mm increments and measure the transmission parameter S. 21 S4. Replace with different pitch helices: Replace with different pitch helices to simulate different velocity factors β; S5. Replace the test piece with a stainless steel vacuum box of equal length, repeat S1-S5 to complete the measurement of the comparison piece; S6. Complete the measurement: Calculate the transmission parameters according to the formula to obtain the transverse coupling impedance.

[0028] Example: A non-relativistic beam transverse coupling impedance measurement device and method based on an off-axis helical slow-wave structure. like Figure 1-8 As shown, the non-relativistic beam transverse coupling impedance measurement device based on an off-axis helical slow-wave structure in this embodiment includes the following four parts: core component, helical assembly, adjustment assembly, and signal processing system: In this embodiment, the core components include a ceramic vacuum chamber, the test piece 1, and a cover plate 2. Ceramic vacuum chamber test piece 1: As the core component of the device, it is used to maintain the vacuum environment required for beam movement and ensure the stability of the measurement environment. For example... Figure 1 The diagram shown is a schematic diagram of the mechanical cross-sectional structure of the core area of ​​the measuring device, illustrating the specific location and structure of the ceramic vacuum box test piece within the device.

[0029] Cover plate 2: Maintains the vacuum area within the vacuum chamber and serves as the positioning base for the measuring device, determining the measurement accuracy of the device. It is tightly fixed to the ceramic vacuum chamber and the workpiece 1 under test via fixing component 3, forming a stable measurement space.

[0030] In this embodiment, the spiral assembly includes a PVC skeleton 4, a spiral wire 5, a coil skeleton pull block 13, and a pull rod 14, wherein... PVC frame 4: Guides and secures the spiral 5, ensuring the stability and accuracy of the spiral during measurement. (Example) Figure 5 The diagram shows the structure of the solenoid coil assembly. The PVC skeleton plays a crucial role as the supporting structure for the solenoid.

[0031] Helix 5: The helical structure reduces the propagation speed of electromagnetic waves in the component under test, simulating the propagation of a non-relativistic beam. The two ends of the helix are connected to the vector network analyzer 11 via copper wires 9 to achieve signal transmission.

[0032] Coil bobbin pull block 13 and pull rod 14: as shown Figure 6 As shown, Figure 5 The enlarged view at the left-hand side shows the role of the coil frame pull block and pull rod in fixing the helix. They fit together tightly, firmly fixing the helix to the PVC frame and preventing the measurement accuracy from being affected by the loosening of the helix.

[0033] In this embodiment, the adjustment assembly includes a vertical displacement adjustment assembly 7 and a horizontal displacement adjustment assembly 8. The vertical displacement adjustment assembly 7 adjusts the helix to be at the vertical center of the vacuum chamber using upper and lower screws, ensuring the precise position of the helix in the vertical direction. The horizontal displacement adjustment assembly 8 adjusts the horizontal position of the helix using horizontal screws, exciting and acquiring electromagnetic field signals for scenarios where the helix is ​​at different horizontal positions. Through fine adjustment, precise control of the cross-sectional position of the helix is ​​achieved.

[0034] In this embodiment, the signal processing system is a vector network analyzer 11, which serves as the signal generation and processing system of the measurement device. It is responsible for sending and receiving test signals, and then calculating the transverse coupling impedance of the beam. Stable signal transmission is achieved by connecting the analyzer to the helical copper wire 5 via cable 12 and adapter 10.

[0035] Other components include, Fixing component 3: Used to securely connect the ceramic vacuum chamber test piece 1 and the cover plate 2, ensuring the stability and sealing of the device during the measurement process. Fixing component 3 can be made of fixing screws.

[0036] Positioning pin 6: Used to ensure that the cover plates 2 at both ends of the vacuum box are on the same horizontal and vertical plane, especially to ensure that the vertical displacement adjustment components 7 and horizontal displacement adjustment components 8 at both ends of the spiral 5 are on the ideal plane, providing a basis for precise adjustment of the spiral position.

[0037] Vertical displacement adjustment component 7 and horizontal displacement adjustment component 8 are used to adjust the vertical and horizontal positions of the helix 5 within the vacuum chamber, respectively, to ensure that the helix is ​​in the ideal measurement plane and improve measurement accuracy. Vertical displacement adjustment component 7 ensures the center position of the helix in the vertical direction, while horizontal displacement adjustment component 8 uses a precision mechanical structure to scan the horizontal offset axis Δ in 10mm steps to obtain the electromagnetic field signal of the helix at different horizontal positions.

[0038] Copper wire 9: Fully electrically connected to the spiral wire 5, used for feeding in signals and receiving signals from the spiral wire 5. The connection between the copper wire and the spiral wire must maintain full electrical connection and be completely insulated from the end metal such as the cover plate 2 to prevent signal interference and ensure the purity and accuracy of the measurement signal.

[0039] Adapter 10: Connects the spiral wire 5 and adjusts the signal input / output interface to adapt to different measurement cable ports, ensuring the stability and compatibility of signal transmission.

[0040] Vector network analyzer 11: As a signal generation and processing system of the measurement device, it is connected to the helical wire 5 through cable 12 and adapter 10, and is responsible for sending test signals and receiving signals, thereby calculating the transverse coupling impedance of the beam.

[0041] The method for performing measurements using the aforementioned non-relativistic beam transverse coupling impedance measurement device based on an off-axis spiral slow-wave structure includes the following steps: Device Setup: Select a suitable spiral wire and, based on the structure of the measuring device, correctly assemble the ceramic vacuum box (test component 1), cover plate 2, PVC frame 4, spiral wire 5, and other components to build a complete measuring device. Figure 3 The diagram shown is an assembly drawing of the measuring device, illustrating the assembly method of each component and the overall structure.

[0042] Instrument Calibration: Turn on the Vector Network Analyzer 11 and allow it to warm up for 30 minutes to reach optimal performance. Then perform instrument calibration to ensure measurement accuracy. The calibration process includes steps such as frequency range setting and transmission line calibration to eliminate systematic errors.

[0043] Center position measurement: The helix is ​​adjusted to the horizontal center position of the vacuum box using the horizontal displacement adjustment component 8. An excitation sweep pulse signal is applied using the vector network analyzer 11 to measure the reflection and transmission parameters of the helix at its center position, particularly the transmission parameter S. 21 This step provides the foundational data for subsequent data analysis.

[0044] Off-axis position scanning: The horizontal off-axis position of the helix is ​​gradually changed in 10mm increments using the horizontal displacement adjustment component 8. At each off-axis position, the transmission parameter S is measured using the vector network analyzer 11. 21 By selecting a step size of 10mm and scanning within a maximum off-axis range of 40mm, sufficient data can be obtained to analyze the impact of different off-axis positions of the helix on the measurement, while effectively reducing measurement errors and preventing accidental damage to measurement data.

[0045] Helix Replacement and Repeated Measurements: Since the non-relativistic beam transverse coupling impedance with different velocity factors β needs to be measured, and the velocity factor β is related to the helix pitch, it is necessary to replace the helix with one of different pitches. After each helix replacement, the above-described center position measurement and off-axis position scanning steps are repeated to obtain the transmission parameters under helices with different pitches.

[0046] Replace the test piece with a stainless steel vacuum box of equal length and repeat the above measurements: Replace the test piece with a stainless steel vacuum box and repeat the above measurement process with different offset axes to obtain the transmission parameters under different pitch helical lines as reference signals in order to deduct the systematic errors of the transmission line and measurement.

[0047] Comparative verification and impedance calculation: Replace the ceramic vacuum box test piece 1 with a stainless steel vacuum box of the same cross-section and length, and measure the transmission parameter S at the same off-axis position. 21 By comparing measurements to subtract systematic errors from transmission lines and measurements, the accuracy and reliability of the measurement results are ensured. Then, according to the formula... Calculate the transverse coupling impedance of the non-relativistic beam. In the formula, ω is the angular frequency, and S... D The transmission parameter S of the vacuum box 21 S R The transmission parameters S of equal-length stainless steel vacuum boxes with the same configuration 21 Characteristic impedance r1 is the radius of the ceramic vacuum box test piece, and r2 is the radius of the spiral formed by the copper wires.

[0048] Results Analysis and Application: By analyzing the impedance sweep frequency results under helices of different pitches, the transverse impedance with a corresponding velocity factor β can be obtained. Velocity factor Where L is the length of the vacuum box, and L is the length of the helix 5. d represents the pitch of the helix. Finally, the lateral coupling impedance of different velocity factors β was measured, providing crucial data support for the performance evaluation of the accelerated vacuum components in the accelerator.

[0049] In this embodiment, screws are used to adjust the horizontal and vertical positions of the helical wire 9 by pushing it upwards. The horizontal adjustment component 8 is adjusted by two screws on the left and right sides, which push it to the horizontal position. Similarly, the vertical adjustment component 7 is adjusted to the vertical position by screws, and four screws on the top and bottom ensure position and balance. This invention is the first to realize non-relativistic transverse impedance measurement using a single off-axis helical copper wire, breaking through the technical bottleneck of the traditional double parallel line method. By reducing the transmission speed of electromagnetic waves in the component under test through the helical copper wire, it simulates the propagation of non-relativistic beams, realizes a slow-wave structure of electromagnetic waves, adapts to the needs of wide-range and high-precision measurement, and improves the signal-to-noise ratio and impedance measurement accuracy in the extremely low frequency domain. By finely adjusting the cross-sectional position of the helical wire, the excitation of the dipole box signal is achieved, realizing non-relativistic transverse impedance measurement. This invention covers an extremely low frequency range, with a high signal-to-noise ratio in the ~10kHz measurement range, providing a reliable solution for high-precision non-relativistic beam transverse impedance measurement.

Claims

1. A method for measuring the transverse coupling impedance of a non-relativistic beam, characterized in that, Includes the following steps: Insert an off-axis spiral copper wire (5) into the ceramic vacuum box (1) to be tested; The propagation speed of electromagnetic waves in the component under test is reduced by using a spiral copper wire (5) to simulate the propagation of a non-relativistic beam. An excitation sweep pulse signal is applied to one end of the copper wire (5) by a vector network analyzer (11), and microwave transmission parameters are obtained at the other end by the vector network analyzer (11). The transverse coupling impedance of the non-relativistic beam is calculated based on the obtained microwave transmission parameters.

2. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that, The spiral copper wire (5) is guided and fixed by the PVC skeleton (4), and its position in the vacuum box is adjusted by the horizontal displacement adjustment component (8) and the vertical displacement adjustment component (7).

3. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 2, characterized in that, The horizontal displacement adjustment component (8) and the vertical displacement adjustment component (7) are used to adjust the horizontal and vertical positions of the helix (5) to excite and acquire electromagnetic field signals of the helix (5) in different position scenarios.

4. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that, The vector network analyzer (11) is connected to the spiral copper wire (5) via a cable (12) and an adapter (10) to send and receive test signals.

5. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that, The measurement method also includes the step of calibrating the vector network analyzer (11) to ensure measurement accuracy.

6. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that, The measurement method measures the transmission parameter S of the spiral (5) at its horizontal center and a set of horizontal off-axis positions. 21 To calculate the transverse coupling impedance of the non-relativistic beam.

7. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 6, characterized in that, The scanning step size for the horizontal off-axis position is 10mm, and the maximum off-axis distance is 40mm, in order to reduce measurement errors and prevent accidental damage to measurement data.

8. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that, The measurement method further includes replacing the ceramic vacuum box test piece (1) with a stainless steel vacuum box of the same cross-section and length, and measuring the transmission parameter S at the same off-axis position. 21 This is to deduct systematic errors from transmission lines and measurements.

9. The method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that, The measurement method measures the transverse coupling impedance of a non-relativistic beam with different velocity factors β by changing the helix (5) with different pitches, where the velocity factor β = L0 / L, L is the length of the vacuum box, and L is the length of the helix (5).

10. A method for measuring the transverse coupling impedance of a non-relativistic beam according to any one of claims 1 to 9, characterized in that, The measurement method utilizes a spiral structure to simulate the propagation speed of a non-relativistic beam in a circular vacuum box, excites real induced electromagnetic waves, and achieves non-relativistic transverse impedance measurement through fine adjustment of the spiral cross-section position, covering an extremely low frequency range and maintaining a high signal-to-noise ratio within the ~10kHz measurement range.

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