Phase drift suppression device and method for superconducting accelerator low-level detection channel

Abstract

The application discloses a kind of inhibiting device and method of superconducting accelerator low level detection channel phase drift, comprising: electric length detection system, reference following system, low level system with slow drift inhibition control function, electric control timing distribution system;The application is arranged with the same length, texture and position layout coaxial cable same as cavity pickup signal acquisition cable, and input radio frequency signal same as reference signal homologous phase.The full reflection signal of electric length detection cable is compared with reference signal in phase, and low level detection signal is compensated according to its phase difference.Finally, the effect of inhibiting superconducting accelerator low level detection channel phase drift is achieved.The structure is simple, the feedback speed is fast, the practical effect is good, and the phase detection accuracy of low level system and the long-term stability of free electron laser device can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of accelerator radio frequency low level, specifically a phase drift suppression device and method for a low level detection path of a superconducting accelerator. Background Technology

[0002] Currently, there are high requirements for the quality of electron beams, such as emission, energy dissipation, and current intensity. Therefore, the amplitude and phase stability of the radio frequency (RF) system within a superconducting accelerator must be within 0.01% and 0.01°, respectively. In the design architecture of traditional low-level RF systems, the electrical length of the probe cable in the detection path changes due to variations in temperature and humidity, introducing a certain error into the phase measurement of the measured signal. In the field of traditional accelerators, this error is small and does not affect the test results. However, in superconducting free-electron laser devices, due to the higher requirements for the stability of the RF signal within the superconducting cavity, any low-frequency measurement noise will affect the cavity field through the feedback loop, thus affecting the beam current. Therefore, this error must be compensated for; otherwise, the system performance will not meet the required specifications.

[0003] Therefore, it is necessary to provide a system and method that can suppress and compensate for the error between the acquired radio frequency signal inside the superconducting cavity and the actual radio frequency field inside the cavity, so as to compensate for the low-frequency drift as much as possible and achieve the required experimental purpose. Summary of the Invention

[0004] This invention patent discloses a device and method for compensating for slow drift in the detection phase of a radio frequency low-level system in a continuous-wave superconducting accelerator. It can effectively compensate for the slow drift in the detection phase caused by temperature and humidity in the detection cable. Furthermore, it can be applied to related accelerators.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A phase drift suppression device for a low-level detection path in a superconducting accelerator includes: an electrically controlled timing distribution system and an electrical length detection system, a reference follower system, and a low-level system connected thereto, respectively. The reference follower system is also connected to the electrical length detection system and the low-level system, respectively.

[0007] The electrical length detection system includes: a reference signal correction amplifier, an electrical length detection signal coupler, and an electrical length detection cable connected in sequence. The end of the electrical length detection cable away from the electrical length detection signal coupler is short-circuited by a short circuit device. The input terminal of the reference signal correction amplifier is connected to a reference follower system, and the coupling terminal of the electrical length detection signal coupler is connected to an electronically controlled timing distribution system.

[0008] The reference following system includes a first-stage reference signal power divider and a second-stage reference signal power divider. The input terminal of the first-stage reference signal power divider is connected to the reference signal, the first output terminal is connected to the low-level system, and the second output terminal is connected to the input terminal of the second-stage reference signal power divider. The first output terminal of the second-stage reference signal power divider is connected to the electronically controlled timing distribution system, and the second output terminal is connected to the input terminal of the reference signal correction amplifier in the electrical length detection system.

[0009] The low-level system includes: a superconducting accelerator low-level device, an excitation power output cable, a low-level detection cable, a detection signal acquisition coupler, and a solid-state amplifier. The superconducting accelerator low-level device is connected to the superconducting accelerator cavity in sequence via the excitation power output cable and the solid-state amplifier. The superconducting accelerator cavity is connected to the input terminal of the detection signal acquisition coupler. The coupling terminal of the detection signal acquisition coupler is connected to the superconducting accelerator low-level device via the low-level detection cable. The superconducting accelerator low-level device is also connected to an electronically controlled timing distribution system.

[0010] The electronically controlled timing distribution system includes an electronically controlled switch and a timing triggering system. The electronically controlled switch is connected to the coupling terminal of the electric length detection signal coupler in the electric length detection system, the second output terminal of the reference signal secondary power divider in the reference follower system, and the low-level device of the superconducting accelerator in the low-level system. The timing triggering system is connected to the electronically controlled switch and the low-level device of the superconducting accelerator in the low-level system.

[0011] The electrical length detection cable and the low-level detection cable are of the same length and model. The short-circuited end of the electrical length detection cable is placed within the threshold range of the coupling end of the detection signal acquisition coupler, and the short-circuited end of the electrical length detection cable is electromagnetically shielded.

[0012] A method for suppressing phase drift in the low-level detection path of a superconducting accelerator includes the following steps:

[0013] The reference signal is split into two paths by the first-stage reference signal power divider. One path is sent to the low-level device of the superconducting accelerator, and the other path is sent to the second-stage reference signal power divider. The second-stage reference signal power divider splits the input reference signal into two paths again. One path is sent to the electronic control switch, and the other path is transmitted to the electric length detection cable through the reference signal correction amplifier and the electric length detection signal coupler in sequence.

[0014] The electrical length detection signal coupler sends the reference signal reflected back from the electrical length detection cable through the coupling end to the electrical control switch as the electrical length detection signal;

[0015] When the timed trigger system controls the electronic switch, the high level in1 is turned on and the low level in2 is turned off. At this time, the low level device of the superconducting accelerator collects the reference signal and completes the reference signal amplitude and phase detection and reference following.

[0016] When the timing signal arrives, the timing trigger system controls the low-level in2 switch of the electronic control switch to be turned on and the high-level in1 switch to be turned off. At this time, the low-level device of the superconducting accelerator collects the electrical length detection signal and demodulates it. The phase of the signal is compared with that of the reference signal to obtain the phase change. The change is then processed to complete the calibration and compensation of the phase drift of the detection path of the target signal, i.e., the cavity pickup signal.

[0017] The reference following of the reference signal is achieved by detecting the amplitude and phase of the reference signal to obtain the detection noise of the measurement path.

[0018] Local oscillator signal phase Phase with reference signal The relationship is:

[0019]

[0020] Among them, f Lo f is the local oscillator frequency. ref For reference frequency, Introducing noise to the local oscillator;

[0021] Low-level sampling clock signal phase Phase with reference signal The relationship is:

[0022]

[0023] Among them, f CLK f is the clock frequency. ref For reference frequency; Introducing noise into the clock;

[0024] Phase of the reference signal under test for:

[0025]

[0026] in, To detect noise, f IF It is an intermediate frequency signal. Noise introduced by signal cables, connectors, or attenuators. Noise introduced by down-conversion of the signal. Noise introduced into the ADC.

[0027] The specific processing of the phase change is as follows:

[0028] Multiply the phase change by This refers to the temperature drift change of the electrical length detection cable, which is used to calibrate and compensate for the phase drift of the detection path of the actual measured signal.

[0029] The present invention has the following beneficial effects and advantages:

[0030] 1. This invention measures the phase of the total internal reflection signal of a cable that coincides with the change in the electrical length of the detection path, and compares it with an initial reference phase. Using a multiple of the measured phase difference as a compensation value to calibrate and compensate for the change in the electrical length of the detection cable can effectively compensate for the slow drift of the detection phase caused by temperature and humidity.

[0031] 2. This invention features a simple structure, fast feedback speed, and good practical results. By controlling the timing of the electronically controlled switches, a single ADC can be used to simultaneously perform phase drift compensation and reference following functions. This effectively reduces system complexity and saves costs.

[0032] 3. Traditional accelerator drift calibration requires bringing the reference signal near the cavity pickup port, which is difficult, costly, and prone to introducing additional noise. This invention utilizes the principle that a short circuit in a transmission line causes total reflection, placing the reference signal within a low-level cabinet, thus reducing the difficulty and cost of implementing drift calibration. Attached Figure Description

[0033] Figure 1 This is a structural diagram of the present invention;

[0034] Figure 2 This is a flowchart of the method of the present invention;

[0035] In the diagram: 1. Electrical length detection cable; 2. Low-level detection cable; 3. Electrical control switch; 4. Reference signal; 5. Electrical length detection signal coupler; 6. Reference follower function signal; 7. Low-level system; 8. Reference signal correction amplifier; 9. Timing trigger system; 10. Electrical control switch output signal; 11. RF power output cable; 12. Detection signal acquisition coupler; 13. Superconducting accelerator cavity; 14. Second-stage reference signal power divider; 15. First-stage reference signal power divider; 16. Solid-state amplifier. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0037] like Figure 1 As shown, the device for suppressing phase drift in the low-level detection path of a superconducting accelerator includes: an electrical length detection system, a reference follower system, a low-level system (7) with slow drift suppression control function, and an electrical control timing distribution system;

[0038] The electrical length detection system includes: an electrical length detection cable (1), preferably with a VSWR of less than 1.10, using an N-type adapter; an electrical length detection signal coupler (5); a reference signal correction amplifier, preferably a low-noise amplifier, with recommended performance: typical NF of 0.5dB and quiescent point gain of 15dB; a reference signal, preferably a reference signal with phase noise below 40fsec at 1.3GHz (4); and a superconducting accelerator low-level system (7) with phase comparison and compensation functions.

[0039] The reference follower system includes: a reference signal, preferably a radio frequency signal with a phase noise of less than 40fsec at 1.3GHz, a first-stage power divider for the reference signal (15), a second-stage power divider for the reference signal (14), and a low-level system with reference follower function;

[0040] The low-level system with slow drift suppression and reference following functions includes: a superconducting accelerator low-level system (7), an RF power output cable, preferably an RF cable with a VSWR of less than 1.10 (11), a low-level detection cable, preferably a low-level detection cable with a VSWR of less than 1.10 (2), a detection signal acquisition coupler (12), and a timing trigger system (9).

[0041] The electronic timing distribution system includes: an electronically controlled switch that uses timing trigger as an enable, preferably a PIN diode RF switch (3), a timing trigger system (9), and a cavity pickup signal detection path;

[0042] The aforementioned superconducting accelerator low-level system (7) includes: an analog board capable of acquiring multiple radio frequency signals and outputting vector modulation signals, and a digital processing board equipped with an FPGA and multiple ADCs. Its main functions include excitation signal generation and adjustment, radio frequency signal acquisition and analog-to-digital conversion, cavity tuning, and feedforward, feedback, and phase compensation of the microwave field within the superconducting cavity. The preferred low-level system is manufactured by the Shanghai Institute of Applied Physics, based on the Zynq series SoC, which has a 16-bit ADC acquisition function. It down-converts the measured radio frequency signal to an intermediate frequency for analog-to-digital conversion and data acquisition, and has a certain amount of BRAM memory space for caching the measured data. It has a DA output and an analog up-conversion channel to generate an adjustable microwave excitation signal, and is equipped with a bandpass filter to filter out harmonics generated during DAC digital-to-analog conversion. It needs to be equipped with a measurement path that is identical to the cavity pickup power detection path configuration, using the same model ADC, the same analog signal transmission channel technology, and the same source local oscillator signal to achieve the reference tracking function and eliminate detection path noise.

[0043] The timing trigger system (9) includes: an enable signal output to the superconducting low level, or a pulse trigger signal (in accelerator pulse operating mode), a solid-state amplifier trigger signal (in accelerator pulse operating mode), and an enable signal for reference following and drift compensation functions. Preferably, the timing trigger system has mains zero-crossing lock, and the clock used by the timing system needs to be frequency divided by: (the least common multiple of the timing system clock period and the low-level sampling clock period / the timing system clock period) times to avoid phase instability relative to the low-level system timing.

[0044] like Figure 2 As shown, the suppression method includes the following steps:

[0045] Step 1: Use a cable of the same type and length as the low-level detection cable (2) as the "electric length detection cable (1)". Preferably, the RF cable with VSWR less than 1.10 is used and the interface is an N-type interface.

[0046] Step 2: Run the low-level detection cable (2) and the electrical length detection cable (1) together. When running the two cables, they should be placed on the same path, with the tunnel end of the electrical length detection cable (1) placed close to the pickup connector as much as possible. This ensures that the temperature changes and mechanical vibrations encountered by the two cables are similar, resulting in consistent changes in electrical length. The end of the electrical length detection cable (1) should be electromagnetically shielded to prevent environmental fields from affecting it.

[0047] Step 3: The reference signal is split into one path using a power divider, and the signal is amplified with low noise and transmitted to the electrical length detection cable (1). The other end of the electrical length detection cable (1) is near the electron gun pickup probe and is in a short-circuit state. Therefore, the signal will be totally reflected back to the low-level cabinet. Outside the low-level cabinet, near the cabinet, there is a directional coupler that can couple the reflected wave out and send it to the RF switch.

[0048] Step 4: The RF switch is controlled by a timing signal. Normally, RF switch in1 is on and in2 is off. At this time, a low level is used to acquire the reference signal (6), realizing the functions of reference signal amplitude and phase detection and reference following. The principle of the reference following function is: by detecting the amplitude and phase of the reference signal, the detection noise of the measurement path can be directly obtained.

[0049] A timing signal is set up by the timer trigger system to enable the electronic switch. This timing signal provides a 2Hz pulse width and 10ms pulse level signal. A high level (in1) enables the acquisition of the RF reference signal. A low level (in2) enables the acquisition of the electrical length detection signal.

[0050] The relationship between the phase of the local oscillator signal and the phase of the reference signal is as follows:

[0051]

[0052] f LO f is the local oscillator frequency. ref This is the reference frequency. Introducing noise into the local oscillator.

[0053] The relationship between the low-level sampling clock signal and the reference signal is as follows:

[0054]

[0055] f CLK f is the clock frequency. ref This is the reference frequency. Introducing noise into the clock.

[0056] Phase of the reference signal under test for:

[0057]

[0058] To detect noise, f IF The intermediate frequency signal (IF signal obtained by low-pass filtering after mixing the reference signal and the local oscillator signal) is obtained by down-converting the high-frequency signal under test. The purpose is to reduce its frequency to a range where the complete information can be acquired by an ADC with a frequency of fclk. Noise introduced by signal cables, connectors, attenuators, and other conditioners. Noise introduced by down-conversion of the signal. Noise introduced into the ADC.

[0059] Therefore, by directly measuring the reference signal using the same low-level signal as a reference, the resulting phase noise is the low-level detection noise. This detection signal's phase can be used as a compensation value to compensate for the measured signal in the cavity; this function is called the reference-following function.

[0060] Step 5: Upon arrival of the timing signal, RF switch in2 is turned on, and in1 is turned off. At this time, the low-level signal is acquired and demodulated to detect the electrical length. This signal is compared with the phase of the previous reference signal. Since only the drift of unidirectional signal transmission needs to be compensated, and the acquired phase change is the phase change of bidirectional transmission due to total internal reflection, the change needs to be multiplied by [the factor needed]. This is the temperature drift change of the electrical length cable (1). This amount is equivalent to the change in the electrical length of the detection cable, and can be used to calibrate and compensate for the phase drift of the detection path of the actual measured signal.

[0061] The timing signal provides a 2Hz pulse width and 10ms pulse level signal. A high level (in1) enables the acquisition of the RF reference signal. A low level (in2) enables the acquisition of the electrical length detection signal.

[0062] The change in the electrical length of the probe cable is temperature-dependent and therefore a slow change. However, due to the fast firmware algorithm, the time used for detecting and comparing the change in electrical length is less than 2µs. The main factor affecting the detection time is the time required to eliminate signal modulation caused by RF switch switching, estimated to be around 10µs. If the switch switching frequency is 10Hz or lower, it will not affect the detection of the reference signal and phase tracking function.

[0063] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A phase drift suppression device for a low-level detection path in a superconducting accelerator, characterized in that, include: An electronically controlled timing distribution system and an electrical length detection system, a reference follower system, and a low-level system connected thereto, wherein the reference follower system is also connected to the electrical length detection system and the low-level system respectively; The electrical length detection system includes: a reference signal correction amplifier, an electrical length detection signal coupler, and an electrical length detection cable connected in sequence. The end of the electrical length detection cable away from the electrical length detection signal coupler is short-circuited by a short circuit device. The input terminal of the reference signal correction amplifier is connected to a reference follower system, and the coupling terminal of the electrical length detection signal coupler is connected to an electronically controlled timing distribution system. The reference following system includes: a first-stage reference signal power divider and a second-stage reference signal power divider. The input terminal of the first-stage reference signal power divider is connected to the reference signal, the first output terminal is connected to the low-level system, and the second output terminal is connected to the input terminal of the second-stage reference signal power divider. The first output terminal of the second-stage reference signal power divider is connected to the electronic control timing distribution system, and the second output terminal is connected to the input terminal of the reference signal correction amplifier in the electric length detection system. The low-level system includes: a superconducting accelerator low-level device, an excitation power output cable, a low-level detection cable, a detection signal acquisition coupler, and a solid-state amplifier. The superconducting accelerator low-level device is connected to the superconducting accelerator cavity via the excitation power output cable and the solid-state amplifier. The superconducting accelerator cavity is connected to the input terminal of the detection signal acquisition coupler, and the coupling terminal of the detection signal acquisition coupler is connected to the superconducting accelerator low-level device via the low-level detection cable. The superconducting accelerator low-level device is also connected to an electronically controlled timing distribution system. The electronically controlled timing distribution system includes an electronically controlled switch and a timing triggering system. The electronically controlled switch is connected to the coupling terminal of the electric length detection signal coupler in the electric length detection system, the second output terminal of the reference signal secondary power divider in the reference follower system, and the low-level device of the superconducting accelerator in the low-level system. The timing triggering system is connected to the electronically controlled switch and the low-level device of the superconducting accelerator in the low-level system.

2. The phase drift suppression device for the low-level detection path of a superconducting accelerator according to claim 1, characterized in that, The electrical length detection cable and the low-level detection cable are of the same length and model. The short-circuited end of the electrical length detection cable is placed within the threshold range of the coupling end of the detection signal acquisition coupler, and the short-circuited end of the electrical length detection cable is electromagnetically shielded.

3. A method for suppressing phase drift in the low-level detection path of a superconducting accelerator, characterized in that, Includes the following steps: The reference signal is split into two paths by the first-stage reference signal power divider. One path is sent to the low-level device of the superconducting accelerator, and the other path is sent to the second-stage reference signal power divider. The second-stage reference signal power divider splits the input reference signal into two paths again. One path is sent to the electronic control switch, and the other path is transmitted to the electric length detection cable through the reference signal correction amplifier and the electric length detection signal coupler in sequence. The electrical length detection signal coupler sends the reference signal reflected back from the electrical length detection cable through the coupling end to the electrical control switch as the electrical length detection signal; When the timed trigger system controls the electronic switch, the high level in1 is turned on and the low level in2 is turned off. At this time, the low level device of the superconducting accelerator collects the reference signal and completes the reference signal amplitude and phase detection and reference following. When the timing signal arrives, the timing trigger system controls the low-level in2 of the electronic control switch to be turned on and the high-level in1 to be turned off. At this time, the low-level device of the superconducting accelerator collects the electrical length detection signal and demodulates it. The phase of the signal is compared with that of the reference signal to obtain the phase change. The change is then processed to complete the calibration and compensation of the phase drift of the detection path of the target to the measured signal, i.e., the cavity pickup signal. The reference following of the reference signal is achieved by detecting the amplitude and phase of the reference signal to obtain the detection noise of the measurement path. Local oscillator signal phase Phase with reference signal The relationship is: in, The local oscillator frequency, For reference frequency, Introducing noise to the local oscillator; Low-level sampling clock signal phase Phase with reference signal The relationship is: in, For clock frequency, For reference frequency; Introducing noise into the clock; Phase of the reference signal under test for: in, To detect noise, It is an intermediate frequency signal. Noise introduced by signal cables, connectors, or attenuators. Noise introduced by down-conversion of the signal. Noise introduced into the ADC.

4. The method for suppressing phase drift in the low-level detection path of a superconducting accelerator according to claim 3, characterized in that, The specific processing of the phase change is as follows: Multiply the phase change by / 2 represents the temperature drift change of the electrical length detection cable. This change is used to calibrate and compensate for the phase drift of the detection path of the actual measured signal.

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