Electron beam length feedback system and method

Abstract

The present application relates to a kind of electron beam length feedback system and method, system includes linear accelerator, radiation device, light splitting device, X-ray transmission diagnostic device, first atomic sensing device, second atomic sensing device and control device, linear accelerator includes the first magnetic compression section and second magnetic compression section for compressing electron beam, first magnetic compression section makes electron beam generate first terahertz radiation, radiation device is used to make electron beam generate X-ray radiation and second terahertz radiation, first atomic sensing device and second sensing device are used to measure the wavelength of first terahertz radiation and second terahertz radiation respectively, control device adjusts linear accelerator according to the wavelength of first terahertz radiation and second terahertz radiation, so that the beam length of electron beam remains unchanged.The electron beam length feedback system and method of the present application can realize the stable electron beam length feedback of high speed, to improve the stability of the long-term radiation characteristics of accelerator.

Description

Technical Field

[0001] This invention relates to the field of electron accelerators, and more specifically to an electron beam long feedback system and method. Background Technology

[0002] X-ray free-electron lasers (XLElas) are the latest generation of synchrotron radiation sources, capable of generating coherent X-ray radiation with ultra-high pulse energy and ultra-short pulses. They are widely used in cutting-edge scientific fields such as physics, chemistry, biology, and materials science. XLElas require extremely high electron beam quality; even minute changes in the beam current can alter radiation characteristics, ultimately leading to instability in X-ray radiation. The most common method for maintaining the radiation stability of XLElas is beam parameter feedback. The bundle length is a key parameter determining the radiation characteristics of an XLElas device, and feedback on the electron beam length is a crucial factor in improving device stability.

[0003] Currently, the electron beam length feedback in X-ray free-electron laser devices mainly uses a bundle length detector to measure the electron beam length, and the feedback of the accelerator bundle length is achieved through the linear accelerator control system. Since the bundle length detector is an electronic device, it has the following shortcomings: 1) When the electron beam bundle length is too short, the bundle length detector is prone to saturation and cannot detect short bundle length electron beams; 2) It determines the electron beam length by detecting the radiation intensity generated after the electron beam passes through the bend, but the radiation intensity is related to the electron beam charge, bundle length, the position and angle of the incident bend, and whether the detector completely receives the radiation. When the electron beam charge changes, the bundle length detector needs to be recalibrated; 3) The bundle length detector signal is greatly affected by changes in ambient temperature and humidity, resulting in significant signal jitter and drift; 4) The measurement response speed is limited by the electronic response speed. Summary of the Invention

[0004] The purpose of this invention is to provide an electron beam long feedback system and method to achieve high-speed and stable electron beam long feedback, thereby improving the stability of the long-term radiation characteristics of the accelerator.

[0005] To achieve the above objectives, the present invention provides an electron beam length feedback system, comprising:

[0006] A linear accelerator includes a first linear acceleration section, a first magnetic compression section, a second linear acceleration section, a second magnetic compression section, and a third linear acceleration section arranged sequentially along the electron beam propagation direction. The first linear acceleration section is used to generate an electron beam with a first preset energy. The first magnetic compression section is used to compress the electron beam with the first preset energy to a first preset beam length and cause the electron beam to generate first terahertz radiation. The second linear acceleration section is used to accelerate the electron beam with the first preset beam length to a second preset energy. The second magnetic compression section is used to compress the electron beam with the second preset energy to a second preset beam length. The third linear acceleration section is used to accelerate the electron beam with the second preset beam length to a third preset energy.

[0007] The radiation device includes an X-ray radiation section and a terahertz radiation section arranged sequentially along the electron beam transmission direction. The X-ray radiation section is used to receive the electron beam accelerated by the third linear acceleration section and generate X-ray radiation from the electron beam. The terahertz radiation section is used to receive the electron beam and X-ray radiation from the X-ray radiation section and generate second terahertz radiation from the electron beam.

[0008] A beam splitter is used to receive the X-ray radiation and the second terahertz radiation transmitted by the terahertz radiation band and to separate the X-ray radiation and the second terahertz radiation.

[0009] An X-ray transmission diagnostic device is used to receive the X-ray radiation separated by the beam splitter and, after performing intensity and spot pattern diagnostics on the X-rays, transmit the X-ray radiation to the beamline.

[0010] A first atomic sensing device is used to receive the first terahertz radiation and detect the wavelength of the first terahertz radiation.

[0011] The second atomic sensing device is used to receive the second terahertz radiation separated by the spectrometer and to detect the wavelength of the second terahertz radiation.

[0012] A control device is connected to the linear accelerator, the first atomic sensing device, and the second atomic sensing device, respectively. It is configured to calculate the beam length of the first electron beam after compression by the first magnetic compression section and the beam length of the second electron beam after compression by the second magnetic compression section based on the wavelength of the first terahertz radiation transmitted by the first atomic sensing device and the wavelength of the second terahertz radiation transmitted by the second atomic sensing device, respectively. The control device adjusts the linear accelerator based on the beam lengths of the first and second electron beams to keep the beam lengths of the first and second electron beams constant.

[0013] Furthermore, the first linear acceleration section includes an electron gun, an injector, an S-segment acceleration tube, and an X-band acceleration tube arranged sequentially along the electron beam transmission direction.

[0014] Furthermore, both the first magnetic compression section and the second magnetic compression section include four dipoles arranged sequentially along the electron beam transmission direction.

[0015] Furthermore, both the second linear acceleration segment and the third linear acceleration segment are C-band accelerator tubes.

[0016] Furthermore, the X-ray radiation section includes multiple short-period oscillators arranged sequentially along the electron beam transmission direction.

[0017] Furthermore, the terahertz radiation segment is a long-period oscillator.

[0018] Furthermore, the beam splitter is a terahertz reflector with a perforation, the size of which is larger than the full spot size of the X-ray radiation and smaller than the full spot size of the terahertz radiation; the transmission direction of the electron beam at the center of the perforation.

[0019] Furthermore, the X-ray transmission diagnostic device includes a gas intensity detector and a fluorescent target. The intensity detector is located in the transmission direction of the electron beam and is used to measure the intensity of X-ray radiation. The fluorescent target can move between the transmission direction of the electron beam and a position deviating from the transmission direction of the electron beam. When the fluorescent target moves to the transmission direction of the electron beam, the fluorescent target measures the spot pattern of the X-ray radiation. When the fluorescent target moves to a position deviating from the transmission direction of the electron beam, the X-ray radiation is transmitted to the beamline.

[0020] Furthermore, both the first and second atomic sensing devices include an alkali metal vapor cell, a first frequency-stabilized laser, a second frequency-stabilized laser, and a spectrometer. The first and second frequency-stabilized lasers emit lasers in opposite directions toward the alkali metal vapor cell. The lasers emitted by the first and second frequency-stabilized lasers simultaneously reach the alkali metal vapor cell, causing the alkali metal atoms to reach a highly excited state along the excitation path. The alkali metal vapor cell receives terahertz radiation, which strikes the highly excited alkali metal atoms, exciting them to a Rydberg state. When the alkali metal atoms in the Rydberg state de-excite to a lower energy level, they generate visible fluorescence. The spectrometer receives the visible fluorescence and obtains the wavelength of the terahertz radiation based on the wavelength of the visible fluorescence.

[0021] Another aspect of the present invention provides an electron beam length feedback method, which is implemented using the electron beam length feedback system described above and includes the following steps:

[0022] The first linear acceleration section of the linear accelerator generates an electron beam with a first preset energy. After passing through the first magnetic compression section, the electron beam with the first preset energy is compressed to a first preset beam length and generates first terahertz radiation. The first terahertz radiation enters the first atomic sensing device, which detects the wavelength of the first terahertz radiation and transmits it to the control device. The electron beam with the first preset beam length is accelerated to a second preset energy through the second linear acceleration section. The electron beam with the second preset energy is compressed to a second preset beam length after passing through the second magnetic compression section. The electron beam with the second preset beam length is accelerated to a third preset energy through the third linear acceleration section. The electron beam with the third preset energy passes through the X-ray radiation section and the terahertz radiation section in sequence and generates X-ray radiation and second terahertz radiation in sequence. The X-ray radiation and the second terahertz radiation are separated after passing through a beam splitter. The separated X-ray radiation enters the X-ray transmission diagnostic device, and the separated second terahertz radiation enters the second atomic sensing device. The second atomic sensing device detects the wavelength of the second terahertz radiation and transmits it to the control device.

[0023] At a preset time, the control device calculates a first initial value of the beam length of the first electron beam after compression by the first magnetic compression section based on the wavelength of the first terahertz radiation transmitted by the first atomic sensing device, and calculates a second initial value of the beam length of the second electron beam after compression by the second magnetic compression section based on the wavelength of the second terahertz radiation transmitted by the second atomic sensing device.

[0024] At any subsequent moment after the preset moment, the control device calculates a first current value of the beam length of the first electron beam based on the wavelength of the first terahertz radiation transmitted by the first atomic sensor, and then adjusts the phase of the X-band accelerating tube of the first linear acceleration section and the intensity of the first magnetic compression section based on the difference between the first current value and the first initial value, so that the beam length of the first electron beam returns to the first initial value; and calculates a second current value of the beam length of the second electron beam based on the wavelength of the second terahertz radiation transmitted by the second atomic sensor, and then adjusts the intensity of the second magnetic compression section based on the difference between the second current value and the second initial value, so that the beam length of the second electron beam returns to the second initial value.

[0025] The electron beam length feedback system and method of the present invention measures the wavelengths of the first terahertz radiation and the second terahertz radiation using a first atomic sensing device and a second atomic sensing device. This allows a control device to calculate the beam lengths of the first and second electron beams based on the wavelengths of the first and second terahertz radiation. By adjusting the phase of the X-band accelerating tube in the first linear acceleration section and the intensity of the first and second magnetic compression sections, the beam lengths of the first and second electron beams are kept constant, thereby improving the stability of the long-term radiation characteristics of the accelerator. Attached Figure Description

[0026] Figure 1This is a structural block diagram of an electron beam length feedback system according to an embodiment of the present invention;

[0027] Figure 2 This is a structural block diagram of a linear accelerator in an electron beam long feedback system according to an embodiment of the present invention;

[0028] Figure 3 This is a structural block diagram of the radiation device of the electron beam long feedback system according to an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the structure of the first magnetic compression section of a linear accelerator according to an embodiment of the present invention;

[0030] Figure 5 This is a structural block diagram of an X-ray transmission diagnostic device for an electron beam length feedback system according to an embodiment of the present invention;

[0031] Figure 6 This is a structural block diagram of the first atom sensing device in an electron beam length feedback system according to an embodiment of the present invention;

[0032] Figure 7 This is a flowchart of an electron beam length feedback method according to an embodiment of the present invention. Detailed Implementation

[0033] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0034] like Figure 1 As shown, this embodiment of the invention provides an electron beam length feedback system, including a linear accelerator 100, a radiation device 200, a beam splitter 300, an X-ray transmission diagnostic device 400, a first atomic sensor 500, a second atomic sensor 600, and a control device 700. The linear accelerator 100, radiation device 200, and beam splitter 300 are arranged sequentially along the electron beam propagation direction on a first axis and located on the same horizontal plane. The linear accelerator 100 is used to generate an electron beam with a continuously adjustable bundle length between 100 femtoseconds and 1 picosecond. Figure 2As shown, the linear accelerator 100 includes a first linear acceleration section 110, a first magnetic compression section 120, a second linear acceleration section 130, a second magnetic compression section 140, and a third linear acceleration section 150 arranged sequentially along the electron beam propagation direction. The first linear acceleration section 110 is used to generate an electron beam with an energy chirp at a first preset energy (e.g., 250 MeV). The first magnetic compression section 120 is used to compress the beam length of the electron beam with the first preset energy to a first preset beam length (e.g., 1-5 picoseconds). The second linear acceleration section 130 is used to accelerate the energy of the electron beam compressed by the first magnetic compression section 120 to a second preset energy (e.g., 680 MeV). The second magnetic compression section 140 is used to compress the beam length of the electron beam accelerated by the second linear acceleration section 130 to a second preset beam length (e.g., 100 femtoseconds to 5 picoseconds), and the third linear acceleration section 150 is used to accelerate the electron beam compressed by the second magnetic compression section 140 to a third preset energy (e.g., 1 GeV). When the electron beam passes through the first magnetic compression section 120, it will generate first terahertz radiation. The wavelength of the first terahertz radiation is related to the beam length of the electron beam compressed by the first magnetic compression section 120 (hereinafter referred to as the first electron beam). The first atomic sensing device 500 is used to receive the first terahertz radiation and detect the wavelength of the first terahertz radiation. Figure 3As shown, the radiation device 200 includes an X-ray radiation section 210 and a terahertz radiation section 220 arranged sequentially along the electron beam propagation direction. The X-ray radiation section 210 is used to receive the electron beam transmitted from the third linear acceleration section 150 and generate wavelength-tunable X-ray radiation from the electron beam. The terahertz radiation section 220 is used to receive the electron beam and X-ray radiation transmitted from the X-ray radiation section 210 and generate second terahertz radiation from the electron beam. The wavelength of the second terahertz radiation is related to the wavelength of the electron beam compressed by the second magnetic compression section 140 (hereinafter referred to as the second electron beam). The beam splitter 300 is used to receive the X-ray radiation and the second terahertz radiation transmitted from the terahertz radiation section 220 and separate the X-ray radiation and the second terahertz radiation (i.e., split them into two transmission paths). The X-ray transmission diagnostic device 400 is used to receive the X-ray radiation separated by the beam splitter 300 and to analyze the X-ray radiation. The intensity and spot size of the radiation are used for diagnosis; the second atomic sensor 600 is used to receive the second terahertz radiation separated by the beam splitter 300 and detect the wavelength of the second terahertz radiation; the control device 700 is connected to the first atomic sensor 500, the second atomic sensor 600 and the linear accelerator 100 respectively (e.g., electrical connection or communication connection), and is used to calculate the beam length of the first electron beam based on the wavelength of the first terahertz radiation detected by the first atomic sensor 500, and to calculate the beam length of the second electron beam based on the wavelength of the second terahertz radiation detected by the second atomic sensor 600. The control device 700 adjusts the parameters of the linear accelerator 700 (including the phase of the X-band accelerating tube of the first linear acceleration section 110, the intensity of the first magnetic compression section 120 and the second magnetic compression section 140) to keep the beam lengths of the first and second electron beams constant.

[0035] The first linear acceleration section 110 includes an electron gun, an injector, an S-band accelerating tube, and an X-band accelerating tube arranged sequentially along the electron beam transmission direction. The energy chirp of the electron beam can be controlled by controlling the phase of the X-band accelerating tube. After the electron beam with energy chirp passes through the first magnetic compression section 120, its beam length is compressed. The beam length of the compressed electron beam is jointly determined by the phase of the X-band accelerating tube and the intensity of the first magnetic compression section 120. In other words, the beam length of the first electron beam can be achieved by adjusting the phase of the X-band accelerating tube and the intensity of the first magnetic compression section 120.

[0036] like Figure 4As shown, the first magnetic compression section 120 includes four dipoles 121 arranged sequentially along the electron beam propagation direction. After the electron beam enters the first magnetic compression section 120, the high-energy head electron beam lags behind due to its outer ring, while the low-energy tail electron beam leads due to its inner ring. This causes the entire electron beam to converge towards the center, ultimately compressing the electron beam cluster. By changing the current in each dipole 121 of the first magnetic compression section 120, the magnetic field of each dipole 121 can be changed, thereby altering the strength of the first magnetic compression section 120.

[0037] In some embodiments, a terahertz reflector (not shown) may be placed after the fourth dipole 121 of the first magnetic compression section 120 (i.e., the dipole 121 near the second linear acceleration section 130) to reflect the first terahertz radiation to the first atomic sensing device 500. The terahertz reflector may be positioned on the extension of the incident direction of the electron beam of the fourth dipole 121, thereby offsetting the terahertz reflector from the exit direction of the electron beam.

[0038] The second linear acceleration section 130 is a C-band accelerating tube used to accelerate the electron beam to a second preset energy.

[0039] The second magnetic compression section 140 has the same structure as the first magnetic compression section 120, and will not be described again here. By using two stages of magnetic compression, the intensity of each compression stage can be reduced, thereby improving the stability of the compressed electron beam length.

[0040] The third linear acceleration section 150 is a C-band accelerating tube used to accelerate the electron beam energy to a third preset energy. At the same time, the tail field and acceleration field of the accelerating tube are used to compensate for the energy chirp of the electron beam, so that the energy space of the electron beam is smooth.

[0041] In some embodiments, the X-ray radiation section 210 may include a plurality of short-period undulators arranged sequentially along the electron beam transmission direction. For example, it may include ten short-period undulators with a period of 16 mm and a length of 4 m. When the electron beam passes through the X-ray radiation section 210, X-ray radiation can be generated, and the wavelength of the X-ray radiation can be adjusted by changing the magnetic gap between each undulator.

[0042] In some embodiments, the terahertz radiation section 220 can be a long-period undulator with a period of 280 mm and a total length of 6 m. When an electron beam that has generated X-ray radiation passes through the long-period undulator, it can generate terahertz radiation. When the resonance relationship of the electron beam is tuned to near the length of the electron beam, the wavelength of the terahertz radiation generated by the electron beam will be consistent with the length of the electron beam.

[0043] In some embodiments, the beam splitter 300 can be a terahertz reflector with a pre-defined aperture. The pre-defined aperture is larger than the full spot size of the X-ray radiation but smaller than the full spot size of the terahertz radiation, allowing X-ray radiation to pass through the aperture while the terahertz radiation is reflected by the reflector, thus separating the X-ray and terahertz radiation. For example, the aperture diameter can be 3 mm. Since the full spot diameter of the X-ray radiation is less than 3 mm, while the full spot diameter of the terahertz radiation is much larger than 3 mm, X-ray radiation can pass unobstructed through the aperture, while the terahertz radiation is reflected. The center of the aperture is located in the direction of electron beam propagation; in an exemplary embodiment, the center of the aperture can be the center of the terahertz reflector.

[0044] The X-ray transmission diagnostic device 400 is located downstream of the beam splitter 300 and in the direction of electron beam transmission to receive the X-ray radiation separated by the beam splitter 300. The X-ray transmission diagnostic device 400 is positioned upstream of the beamline to transmit the X-ray radiation downstream after diagnostic work is completed. Figure 5 As shown, the X-ray transmission diagnostic device 400 may include a gas intensity detector 410 and a fluorescence target 420. The intensity detector 410 is located in the transmission direction of the electron beam and is used to measure the intensity of X-ray radiation. The fluorescence target 420 can move between the transmission direction of the electron beam and a position deviating from the transmission direction of the electron beam. When the fluorescence target 420 moves to the transmission direction of the electron beam, it can measure the spot pattern of the X-ray radiation. When the fluorescence target 420 moves to a position deviating from the transmission direction of the electron beam, the X-ray radiation can be transmitted to the downstream beamline. By judging whether the intensity and spot pattern of the X-ray radiation are stable, the actual effect of the electron beam length feedback can be judged. When both the intensity and spot pattern of the X-ray radiation remain stable, it indicates that the beam length feedback effect is good; otherwise, it indicates that the beam length feedback effect is poor.

[0045] like Figure 6As shown, the first atomic sensing device 500 includes an alkali metal vapor cell 510, a first frequency-stabilized laser 520, a second frequency-stabilized laser 530, and a spectrometer 540. The alkali metal vapor cell 510 is located in the transmission direction of the first terahertz radiation. The first frequency-stabilized laser 520 and the second frequency-stabilized laser 530 emit lasers into the alkali metal vapor cell in opposite directions. The lasers emitted by the first frequency-stabilized laser 520 and the second frequency-stabilized laser 530 arrive at the alkali metal vapor cell simultaneously, causing the alkali metal atoms to reach a highly excited state along the excitation path. When the first terahertz radiation enters the alkali metal vapor cell and strikes the highly excited alkali metal atoms, the alkali metal atoms are excited to the Rydberg state. When the atoms in the Rydberg state de-excite to a lower energy level, visible fluorescence is generated. The spectrometer 540 is used to receive the visible fluorescence and measure its wavelength. By calibrating the wavelength of the visible fluorescence, the wavelength of the first terahertz radiation can be deduced. The spectrometer 540 is connected to the control device 700, thereby transmitting the wavelength of the first terahertz radiation to the control device 700.

[0046] In one exemplary embodiment, the alkali metal vapor cell 510 is a cesium or rubidium atomic vapor cell with a quartz shell, the area of ​​the vapor cell is 1 square centimeter, and the vapor cell is heated to 50 degrees Celsius during operation.

[0047] The structure of the second atomic sensing device 600 is exactly the same as that of the first atomic sensing device 500, and will not be described again here. The atomic sensing device of the present invention has the characteristics of high sensitivity and high speed in detecting terahertz radiation wavelengths.

[0048] In some embodiments, the control device 700 may first obtain an initial value of the first electron beam length at a certain moment using the wavelength of the first terahertz radiation, and then obtain an initial value of the second electron beam length at that moment using the wavelength of the second terahertz radiation. At any subsequent moment, the control device 700 obtains the first electron beam length and the second electron beam length at that subsequent moment based on the wavelengths of the first and second terahertz radiation, respectively. Then, it compares the first electron beam length at that subsequent moment with the initial value of the first electron beam length to obtain the difference between the two, and calculates the first linear acceleration segment 1 that needs adjustment based on the difference. The phase of the X-band accelerating tube 10 and the intensity of the first magnetic compression section 120 are calculated, and then the phase of the X-band accelerating tube 10 and the intensity of the first magnetic compression section 120 are adjusted to the calculated values ​​so that the length of the first electron beam at subsequent moments returns to the initial value; at the same time, the control device 700 compares the length of the second electron beam at the subsequent moment with the initial value of the length of the second electron beam, obtains the difference between the two, calculates the intensity of the second magnetic compression section 140 that needs to be adjusted based on the difference, and then adjusts the intensity of the second magnetic compression section 140 to the calculated value so that the length of the second electron beam at subsequent moments returns to the initial value.

[0049] The electron beam length feedback system of this invention measures the wavelengths of the first and second terahertz radiation using a first atomic sensor 500 and a second atomic sensor 600. This allows a control device 700 to calculate the beam lengths of the first and second electron beams based on their wavelengths. By adjusting the phase of the X-band accelerating tube in the first linear acceleration section 110 and the intensity of the first magnetic compression section 120 and the second magnetic compression section 140, the beam lengths of the first and second electron beams are kept constant, thereby improving the stability of the accelerator's long-term radiation characteristics.

[0050] like Figure 7 As shown, another embodiment of the present invention provides an electron beam length feedback method, which is implemented using the electron beam length feedback system as described in the above embodiments and includes the following steps:

[0051] S100: The first linear acceleration section 110 of the linear accelerator 100 generates an electron beam with a first preset energy. This electron beam, after passing through the first magnetic compression section 120, is compressed to a first preset beam length and generates first terahertz radiation. The first terahertz radiation enters the first atomic sensing device 500, which detects the wavelength of the first terahertz radiation and transmits it to the control device 700. The electron beam with the first preset beam length is accelerated to a second preset energy through the second linear acceleration section 130. The electron beam with the second preset energy is compressed to a second preset energy after passing through the second magnetic compression section 140. The second preset beam length; the electron beam of the second preset beam length is accelerated to the third preset energy through the third linear acceleration section. The electron beam of the third preset energy passes through the X-ray radiation section 210 and the terahertz radiation section 220 in sequence to generate X-ray radiation and second terahertz radiation in sequence. The X-ray radiation and second terahertz radiation are separated after passing through the beam splitter. The separated X-ray radiation enters the X-ray transmission diagnostic device 400. The separated second terahertz radiation enters the second atomic sensing device 600. The second atomic sensing device 600 detects the wavelength of the second terahertz radiation and transmits it to the control device 700.

[0052] S200: At a preset time, the control device 700 calculates a first initial value of the beam length of the first electron beam passing through the first magnetic compression section 120 based on the wavelength of the first terahertz radiation transmitted by the first atomic sensor 500, and calculates a second initial value of the beam length of the second electron beam passing through the second magnetic compression section 140 based on the wavelength of the second terahertz radiation transmitted by the second atomic sensor 600.

[0053] S300: At any time after the preset time, the control device 700 calculates the first current value of the beam length of the first electron beam based on the wavelength of the first terahertz radiation transmitted by the first atomic sensor 500, and then adjusts the phase of the X-band accelerating tube of the first linear accelerating section 110 and the intensity of the first magnetic compression section 120 based on the difference between the first current value and the first initial value, so that the beam length of the first electron beam returns to the first initial value; and calculates the second current value of the beam length of the second electron beam based on the wavelength of the second terahertz radiation transmitted by the second atomic sensor 600, and then adjusts the intensity of the second magnetic compression section 140 based on the difference between the second current value and the second initial value, so that the beam length of the second electron beam returns to the second initial value.

[0054] The electron beam length feedback method of this invention measures the wavelengths of the first terahertz radiation and the second terahertz radiation using a first atomic sensor 500 and a second atomic sensor 600. This allows a control device 700 to calculate the beam lengths of the first and second electron beams based on their wavelengths. By adjusting the phase of the X-band accelerating tube in the first linear accelerating section 110 and the intensity of the first magnetic compression section 120 and the second magnetic compression section 140, the beam lengths of the first and second electron beams are kept constant, thereby improving the stability of the accelerator's long-term radiation characteristics.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. An electron beam long feedback system, characterized in that, include: A linear accelerator includes a first linear acceleration section, a first magnetic compression section, a second linear acceleration section, a second magnetic compression section, and a third linear acceleration section arranged sequentially along the electron beam propagation direction. The first linear acceleration section is used to generate an electron beam with a first preset energy. The first magnetic compression section is used to compress the electron beam with the first preset energy to a first preset beam length and cause the electron beam to generate first terahertz radiation. The second linear acceleration section is used to accelerate the electron beam with the first preset beam length to a second preset energy. The second magnetic compression section is used to compress the electron beam with the second preset energy to a second preset beam length. The third linear acceleration section is used to accelerate the electron beam with the second preset beam length to a third preset energy. The radiation device includes an X-ray radiation section and a terahertz radiation section arranged sequentially along the electron beam transmission direction. The X-ray radiation section is used to receive the electron beam accelerated by the third linear acceleration section and generate X-ray radiation from the electron beam. The terahertz radiation section is used to receive the electron beam and X-ray radiation from the X-ray radiation section and generate second terahertz radiation from the electron beam. A beam splitter is used to receive the X-ray radiation and the second terahertz radiation transmitted by the terahertz radiation band and to separate the X-ray radiation and the second terahertz radiation. An X-ray transmission diagnostic device is used to receive the X-ray radiation separated by the beam splitter and, after performing intensity and spot pattern diagnostics on the X-rays, transmit the X-ray radiation to the beamline. A first atomic sensing device is used to receive the first terahertz radiation and detect the wavelength of the first terahertz radiation. The second atomic sensing device is used to receive the second terahertz radiation separated by the spectrometer and to detect the wavelength of the second terahertz radiation. A control device is connected to the linear accelerator, the first atomic sensing device, and the second atomic sensing device, respectively. It is configured to calculate the beam length of the first electron beam after compression by the first magnetic compression section and the beam length of the second electron beam after compression by the second magnetic compression section based on the wavelength of the first terahertz radiation transmitted by the first atomic sensing device and the wavelength of the second terahertz radiation transmitted by the second atomic sensing device, respectively. The control device adjusts the linear accelerator based on the beam lengths of the first and second electron beams to keep the beam lengths of the first and second electron beams constant.

2. The electron beam length feedback system according to claim 1, characterized in that, The first linear acceleration section includes an electron gun, an injector, an S-segment acceleration tube, and an X-segment acceleration tube arranged sequentially along the electron beam transmission direction.

3. The electron beam length feedback system according to claim 1, characterized in that, Both the first magnetic compression section and the second magnetic compression section include four diodes arranged sequentially along the electron beam transmission direction.

4. The electron beam length feedback system according to claim 1, characterized in that, Both the second linear acceleration segment and the third linear acceleration segment are C-band accelerator tubes.

5. The electron beam length feedback system according to claim 1, characterized in that, The X-ray radiation section includes multiple short-period oscillators arranged sequentially along the electron beam propagation direction.

6. The electron beam length feedback system according to claim 1, characterized in that, The terahertz radiation section is a long-period oscillator.

7. The electron beam length feedback system according to claim 1, characterized in that, The beam splitter is a terahertz reflector with a cutout, the size of which is larger than the full spot size of the X-ray radiation but smaller than the full spot size of the terahertz radiation; the center of the cutout is in the direction of electron beam propagation.

8. The electron beam length feedback system according to claim 1, characterized in that, The X-ray transmission diagnostic device includes a gas intensity detector and a fluorescent target. The intensity detector is located in the transmission direction of the electron beam and is used to measure the intensity of X-ray radiation. The fluorescent target can move between the transmission direction of the electron beam and a position deviating from the transmission direction of the electron beam. When the fluorescent target moves to the transmission direction of the electron beam, the fluorescent target measures the spot pattern of the X-ray radiation. When the fluorescent target moves to a position deviating from the transmission direction of the electron beam, the X-ray radiation is transmitted to the beamline.

9. The electron beam length feedback system according to claim 1, characterized in that, Both the first and second atomic sensing devices include an alkali metal vapor cell, a first frequency-stabilized laser, a second frequency-stabilized laser, and a spectrometer. The first and second frequency-stabilized lasers emit lasers in opposite directions toward the alkali metal vapor cell. The lasers emitted by the first and second frequency-stabilized lasers arrive at the alkali metal vapor cell simultaneously, causing the alkali metal atoms to reach a highly excited state along the excitation path. The alkali metal vapor cell receives terahertz radiation, which strikes the highly excited alkali metal atoms, exciting them to a Rydberg state. When the alkali metal atoms in the Rydberg state de-excite to a lower energy level, they produce visible fluorescence. The spectrometer receives the visible fluorescence and obtains the wavelength of the terahertz radiation based on the wavelength of the visible fluorescence.

10. An electron beam length feedback method, characterized in that, The electron beam length feedback system as described in any one of claims 1-9 is used and includes the following steps: The first linear acceleration section of the linear accelerator generates an electron beam with a first preset energy. After passing through the first magnetic compression section, the electron beam with the first preset energy is compressed to a first preset beam length and generates first terahertz radiation. The first terahertz radiation enters the first atomic sensing device, which detects the wavelength of the first terahertz radiation and transmits it to the control device. The electron beam with the first preset beam length is accelerated to a second preset energy through the second linear acceleration section. The electron beam with the second preset energy is compressed to a second preset beam length after passing through the second magnetic compression section. The electron beam with the second preset beam length is accelerated to a third preset energy through the third linear acceleration section. The electron beam with the third preset energy passes through the X-ray radiation section and the terahertz radiation section in sequence and generates X-ray radiation and second terahertz radiation in sequence. The X-ray radiation and the second terahertz radiation are separated after passing through a beam splitter. The separated X-ray radiation enters the X-ray transmission diagnostic device, and the separated second terahertz radiation enters the second atomic sensing device. The second atomic sensing device detects the wavelength of the second terahertz radiation and transmits it to the control device. At a preset time, the control device calculates a first initial value of the beam length of the first electron beam after compression by the first magnetic compression section based on the wavelength of the first terahertz radiation transmitted by the first atomic sensing device, and calculates a second initial value of the beam length of the second electron beam after compression by the second magnetic compression section based on the wavelength of the second terahertz radiation transmitted by the second atomic sensing device. At any subsequent moment after the preset moment, the control device calculates a first current value of the beam length of the first electron beam based on the wavelength of the first terahertz radiation transmitted by the first atomic sensor, and then adjusts the phase of the X-band accelerating tube of the first linear acceleration section and the intensity of the first magnetic compression section based on the difference between the first current value and the first initial value, so that the beam length of the first electron beam returns to the first initial value; and calculates a second current value of the beam length of the second electron beam based on the wavelength of the second terahertz radiation transmitted by the second atomic sensor, and then adjusts the intensity of the second magnetic compression section based on the difference between the second current value and the second initial value, so that the beam length of the second electron beam returns to the second initial value.

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