CN-122017350-A - Non-relativistic beam transverse coupling impedance measurement method

Abstract

The invention belongs to the field of accelerator physics and microwave measurement intersection, and relates to a non-relativity beam transverse coupling impedance measurement method based on an off-axis spiral line slow wave structure; the method comprises the steps of inserting an off-axis spiral copper wire into a ceramic vacuum box to be tested, guiding and fixing the ceramic vacuum box through a PVC framework, finely adjusting the position of the ceramic vacuum box through a horizontal and vertical displacement adjusting assembly, simulating non-relativity beam propagation, applying excitation sweep pulse signals to two ends of the copper wire through a vector network analyzer, acquiring microwave transmission parameters, and accordingly calculating transverse coupling impedance.

Inventors

• HUANG LIANGSHENG
• LIU RENHONG
• TAN BIAO
• HUANG MINGYANG
• CHEN SHENGYI
• ZENG LIRUI
• WANG PENGCHENG

Assignees

• 中国科学院高能物理研究所
• 散裂中子源科学中心

Dates

Publication Date

20260512

Application Date

20260311

Claims (10)

1. 1. The non-relativistic beam transverse coupling impedance measurement method is characterized by comprising the following steps of: Inserting an off-axis spiral copper wire (5) into the ceramic vacuum box (1) to be tested; Reducing the transmission speed of electromagnetic waves in the component to be tested through a spiral copper wire (5) so as to simulate the propagation of non-relativity beam; Applying an excitation sweep pulse signal to one end of a copper wire (5) by a vector network analyzer (11), and acquiring microwave transmission parameters by the vector network analyzer (11) at the other end; and calculating the transverse coupling impedance of the non-relativity beam according to the acquired microwave transmission parameters.
2. 2. A method according to claim 1, characterized in that the spiral copper wire (5) is guided and fixed by a PVC skeleton (4) and its position in the vacuum box is adjusted by a horizontal displacement adjusting assembly (8) and a vertical displacement adjusting assembly (7).
3. 3. A method according to claim 2, wherein the horizontal displacement adjusting component (8) and the vertical displacement adjusting component (7) are respectively used for adjusting the horizontal position and the vertical position of the spiral line (5) so as to excite and acquire electromagnetic field signals of scenes where the spiral line (5) is at different positions.
4. 4. A method of measuring non-relativistic beam transverse coupling impedance 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 a adapter (10) for transmitting test signals and receiving signals.
5. 5. A method of measuring non-relativistic beam transverse coupling impedance according to claim 1, characterized in that the method further comprises the step of calibrating the vector network analyzer (11) to ensure measurement accuracy.
6. 6. A method for measuring the transverse coupling impedance of a non-relativistic beam according to claim 1, characterized in that the method calculates the transverse coupling impedance of the non-relativistic beam by measuring the transmission parameters S 21 of the spiral (5) at a horizontal center and a set of horizontal off-axis positions.
7. 7. The method of claim 6, wherein the scanning step size of the horizontal off-axis position is 10mm and the maximum off-axis distance is 40mm, so as to reduce measurement errors and prevent accidental damage to the measurement data.
8. 8. The method according to claim 1, further comprising replacing the ceramic vacuum box to be measured (1) with a stainless steel vacuum box of the same cross section and equal length, measuring the transmission parameters S 21 at the same off-axis position to subtract the transmission line and the measured systematic errors.
9. 9. A method according to claim 1, characterized in that the method is used for measuring the transverse coupling impedance of the non-relativistic beam by changing the spiral (5) with different pitches, wherein the speed factor β=l0/L, L being the length of the vacuum box and L being the length of the spiral (5).
10. 10. A method for measuring transverse coupling impedance of non-relativistic beams according to any of claims 1-9, characterized in that it uses a spiral structure to simulate the propagation speed of non-relativistic beams in a circular vacuum box, excites real induced electromagnetic waves, and realizes non-relativistic transverse impedance measurement by fine adjustment of the position of the spiral cross section, covering very low frequency range and maintaining high signal-to-noise ratio in the measuring range of 10 kHz.

Description

Non-relativistic beam transverse coupling impedance measurement method Technical Field The invention belongs to the technical cross field of accelerator physics and microwave measurement, and particularly relates to a non-relativity beam transverse coupling impedance measurement method based on an off-axis spiral line slow wave structure. Background Accurate measurement of beam coupling impedance is a key method of evaluating the performance of accelerating vacuum components in modern accelerators. In the accelerator technology, the transverse coupling impedance of the beam directly affects the stability and transmission efficiency of the beam, so that accurate measurement of the transverse coupling impedance has important significance for optimizing the design of the accelerator and improving the quality of the beam. Currently, the industry commonly adopts a double parallel line method to measure transverse impedance. The method comprises the steps of inserting a pair of parallel transmission lines into a vacuum component to be measured, introducing opposite excitation signals, measuring frequency domain reflection and transmission parameters by using a vector network analyzer, and calculating impedance. However, the double parallel line method has a significant limitation in that, first, the electromagnetic field generated by the vector network analyzer can only propagate at the speed of light in the vacuum box, so that theoretically only a scene in which the beam speed is at the speed of light, that is, the speed factor β=v/c=1 of the beam can be measured. In practical accelerators, however, the velocity of the charged particles is typically 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 the non-relativistic beam. Secondly, when the measurement frequency band is reduced to below 10MHz, the electromagnetic coupling efficiency between the two wires is drastically reduced, and the transmission signal amplitude is completely submerged by the instrument noise floor, so that an effective signal cannot be obtained. This problem is particularly pronounced in the very low frequency domain, severely limiting the range of application of the double parallel line approach. In view of the above, it has been internationally explored how to generate a slow wave electromagnetic field structure to simulate the propagation of a non-relativistic beam in a vacuum component and to achieve high-precision transverse coupling impedance measurement. However, the conventional method has a technical bottleneck in realizing the slow wave structure, and is difficult to meet the requirement of high-precision measurement. Disclosure of Invention Aiming at the problems, the invention aims to provide a non-relativistic beam transverse coupling impedance measurement method based on an off-axis spiral line slow wave structure, which focuses on transverse coupling impedance measurement of non-relativistic beam (speed factor beta < 1), breaks through the technical limitations of the traditional measurement method in non-relativistic scenes and low frequency bands, and provides an innovative solution for performance evaluation of accelerator vacuum components. The technical scheme adopted by the invention for solving the technical problems is that the method for measuring the transverse coupling impedance of the non-relativity beam comprises the following steps: inserting an off-axis spiral copper wire into the ceramic vacuum box to be tested; Reducing the transmission speed of electromagnetic waves in a component to be tested through a spiral copper wire so as to simulate the propagation of non-relativity beam current; applying an excitation sweep pulse signal to one end of the copper wire by a vector network analyzer, and acquiring microwave transmission parameters by the vector network analyzer at the other end; and calculating the transverse coupling impedance of the non-relativity beam according to the acquired microwave transmission parameters. The spiral copper wire is guided and fixed through the PVC framework, and the position of the spiral copper wire in the vacuum box is adjusted through the horizontal displacement adjusting assembly and the vertical displacement adjusting assembly. The horizontal displacement adjusting component and the vertical displacement adjusting component are respectively used for adjusting the horizontal position and the vertical position of the spiral line so as to excite and acquire electromagnetic field signals of scenes where the spiral line is at different positions. The vector network analyzer is connected with the spiral line copper wire through a cable and an adapter to send test signals and receive signals. The measurement method further comprises the step of calibrating the vector network analyzer to ensure measurement accuracy. The measuring method calculates the