Method for measuring electron beam and seed light arrival time jitter in free electron laser

Abstract

The application relates to a kind of free electron laser electron beam and seed light arrival time jitter measurement methods, which utilize modulation section wave oscillator to realize energy exchange of electron beam and seed light in time t direction coincidence part, thereby forming energy modulation with seed light wavelength as period, utilize dispersion section to realize density modulation of electron beam in time t direction, utilize radiation section wave oscillator to realize amplification of radiation field, utilize microwave deflection cavity to realize conversion of electron beam time direction information to X direction of the plane where beam measurement target is located, utilize deflection magnet to realize conversion of electron beam energy direction information to Y direction of the plane where beam measurement target is located, and finally realize the purpose of detecting electron beam and seed light arrival time relative jitter by detecting the distance between complete electron beam center line on beam measurement target and the center line of the part where electron beam and seed light coincide.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of external seed free electron laser, in particular to a method for measuring the arrival time jitter of electron beam and seed light in free electron laser. BACKGROUND

[0002] External seed free electron laser has the advantages of narrow spectrum width and high stability, and has incomparable advantages over other light sources in the fields of physical chemistry and material science. The above advantages of external seed free electron laser are caused by the modulation of seed light to electron beam, and the stability of the coincidence of the arrival time of electron beam and seed light plays an important role in the light stability of free electron laser. In order to maintain and diagnose the light state of external seed free electron laser, it is necessary to measure the relative jitter of the arrival time of electron beam and seed light online. SUMMARY

[0003] The purpose of the present application is to provide a method for measuring the arrival time jitter of electron beam and seed light in free electron laser, which can convert the time direction information and energy direction information of electron beam to the X direction and Y direction of the plane where the beam measurement target is located respectively, and realize the purpose of detecting the relative jitter of the arrival time of electron beam and seed light by detecting the distance between the complete electron beam center line and the center line of the overlapping part of electron beam and seed light on the beam measurement target.

[0004] The purpose of the present application is achieved by the following technical scheme:

[0005] A method for measuring the arrival time jitter of electron beam and seed light in free electron laser, comprising the following steps:

[0006] Step one, the electron beam and the seed light are injected into a modulation section undulator, and the electron beam performs torsional motion in the modulation section undulator, and the overlapping part of the electron beam and the seed light in the time t direction forms energy modulation with the wavelength of the seed light as the period through energy exchange;

[0007] Step two, the electron beam emitted from the modulation section undulator is injected into a dispersion section, and the electron beams with different energies pass through different paths in the dispersion section and form corresponding period groupings to realize density modulation;

[0008]

[0008] Step three, the electron beam emitted from the dispersion section is injected into a radiation section undulator, and the energy distribution of the electron beam is widened in the radiation section undulator;

[0009] Step four, the electron beam emitted from the radiation section undulator is injected into a microwave deflection cavity, and when viewed along the vertical direction, the electron beam is deflected by the deflection force of the microwave in the microwave deflection cavity to the horizontal X' direction perpendicular to the time t direction;

[0010] Step 5: The electron beam emitted from the microwave deflection cavity is injected into a deflection magnet. Due to the different magnetic stiffness of electrons with different energies, the deflection radius of electrons with different energies after being emitted from the deflection magnet is different in the vertical direction.

[0011] Step Six: The electron beam emitted by the deflecting magnet is projected onto a target beam. The centerline of the complete electron beam is l1, and the centerline of the portion of the electron beam that overlaps with the seed light is l2. The distance between l1 and l2 is the deviation Δx, and the relative arrival time Δt between the electron beam and the seed light is:

[0012] Δt=k·Δx (1);

[0013] In equation (1) above, k is the time conversion coefficient;

[0014] Step 7: Monitor the relative arrival time Δt within a set time period and calculate the standard deviation to obtain the relative jitter of the arrival time of the electron beam and the seed light.

[0015] The modulation segment undulator includes multiple permanent magnets arranged in a straight line, with permanent magnets of opposite polarities alternating. The electron beam and seed light pass through each permanent magnet in sequence, and the electron beam undergoes a torsional motion due to the action of the alternating permanent magnets.

[0016] In step one, the electron beam and the seed light interact in the modulation section undulator, where the overlapping portion of the electric field strength E>0 of the electron beam and the seed light loses energy, and the overlapping portion of E<0 gains energy.

[0017] The dispersion section includes four secondary magnets, wherein the first and fourth magnets are located on the beam path, the second and third magnets are located between the first and fourth magnets, and the second and third magnets are located on the same side of the beam path.

[0018] In step three, after energy modulation and density modulation, the part of the electron beam that overlaps with the seed light in the time t direction generates a micro-beam cluster. By setting the parameters of the radiation section undulator (3), the first harmonic component in the micro-beam cluster resonates with the radiation section undulator to generate radiation. The electron beam exchanges energy with the radiation field to realize radiation field amplification. The electron beam loses energy and the energy distribution of the electron beam becomes wider.

[0019] In step four, the microwave deflection cavity has a disk-loaded waveguide structure inside.

[0020] In step five, the deflection radius of an electron with energy p under the B0 magnetic field is:

[0021]

[0022] In the above formula, p is the electron beam energy, e is the electron beam charge, B0 is the magnetic field strength, and ρ is the electron beam radius.

[0023] In step six, the time conversion coefficient k is changed by altering the microwave phase Δφ of the microwave deflection cavity and observing the displacement Δx of l1 on the beam measurement target. φ The result was obtained after calculation:

[0024]

[0025] In equation (2) above, f is the microwave frequency of the microwave deflection cavity.

[0026] The advantages and positive effects of this invention are as follows:

[0027] 1. This invention utilizes a microwave deflection cavity to convert the time direction information of the electron beam to the X direction of the plane where the beam measurement target is located. When the electron beam passes through the microwave deflection cavity, viewed from a perpendicular perspective, the microwaves within the cavity exert different deflection forces on the beginning and end of the electron beam, thus deflecting the incident electron beam towards a horizontal X′ direction perpendicular to time t, forming the outgoing electron beam. When the electron beam passes through the deflection magnet and strikes the beam measurement target, such as... Figure 7 As shown, the electron beam at different times t transforms into different positions along the horizontal X direction on the plane where the beam measurement target is located.

[0028] 2. This invention utilizes a deflecting magnet to convert the energy direction information of the electron beam to the Y-direction of the plane where the beam measurement target is located. Because electrons of different energies have different magnetic stiffness, when the electron beam passes through the deflecting magnet, electrons of different energies deflect in the vertical direction with different radii, thus achieving... Figure 7 As shown, when an electron beam strikes a beam measuring target, electron beams of different energies are distributed at different positions in the vertical Y-direction of the plane containing the beam measuring target.

[0029] 3. This invention utilizes a modulation segment undulator to achieve energy exchange between the electron beam and the seed light in the overlapping portion of the time t direction, thereby forming an energy modulation segment with the seed light wavelength as the period. It also utilizes a dispersion segment to achieve density modulation of the electron beam in the time t direction and a radiation segment undulator to amplify the radiation field. The electron beam loses energy and the energy distribution of the electron beam becomes wider, so that the electron beam image formed on the beam measurement target meets the measurement requirements, thereby ensuring the detection of relative jitter in the arrival time of the electron beam and the seed light. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the device of the present invention.

[0031] Figure 2 for Figure 1 Schematic diagram of the structure and principle of the mid-modulation section undulator and the radiation section undulator.

[0032] Figure 3This is a schematic diagram illustrating the principle of electron beam modulation by seed light energy in the modulation section undulator.

[0033] Figure 4 for Figure 1 A schematic diagram illustrating the structural principle of the intermediate dispersion section.

[0034] Figure 5 for Figure 1 A schematic diagram illustrating the working principle of a microwave deflection cavity.

[0035] Figure 6 for Figure 5 A schematic diagram of the cross-sectional structure of a medium-wave deflection cavity.

[0036] Figure 7 for Figure 1 A schematic diagram of the beam spot on the mid-beam target.

[0037] Among them, 1 is the modulation section undulator, 2 is the dispersion section, 201 is the first magnet, 202 is the second magnet, 203 is the third magnet, 204 is the fourth magnet, 3 is the radiation section undulator, 4 is the microwave deflection cavity, 5 is the deflection magnet, 6 is the beam measurement target, 7 is the electron beam, 8 is the seed light, 9 is the incident electron beam, 10 is the outgoing electron beam, and 11 is the permanent magnet. Detailed Implementation

[0038] The invention will now be described in further detail with reference to the accompanying drawings.

[0039] like Figures 1 to 7 As shown, the device of the present invention includes a free-electron laser device, and the electron beam emitted by the free-electron laser device sequentially passes through a modulation section undulator 1, a dispersion section 2, a radiation section undulator 3, a microwave deflection cavity 4, and a deflection magnet 5 before being projected onto a beam measurement target 6. The free-electron laser device is a well-known technology in the art and is a commercially available product. In this embodiment, the electron beam emitted by the free-electron laser device needs to have high energy (>100MeV) and low emissivity, and the seed light needs to have a megawatt-level output power.

[0040] In the modulation undulator 1, the electron beam is modulated by the energy of the seed light to form an energy distribution with a period of the seed light wavelength, wherein, for example... Figure 2 As shown, in this embodiment, the modulation segment undulator 1 is a planar undulator, which includes multiple permanent magnets 11 arranged in a straight line, with permanent magnets 11 of opposite polarities alternately arranged. The electron beam and seed light pass through each permanent magnet 11 in sequence, wherein the electron beam undergoes a torsional motion under the influence of the alternately arranged permanent magnets 11, and simultaneously... Figure 3 As shown, under the set parameters of the modulation segment undulator 1, the electron beam 7 and the seed light 8 will interact in the modulation segment undulator 1, wherein the overlapping portion of the electron beam 7 and the seed light 8 with the electric field strength E>0 loses energy (i.e., Figure 3The peak of the E wave corresponds to the trough where the p energy decreases, and the part where E < 0 yields the energy (i.e., Figure 3 The trough of the electron beam 7 is converted into a peak with increased p energy. Therefore, at the exit of the modulation section undulator 1, the portion of the energy p of the electron beam 7 that coincides with the seed light 8 in the time t direction (which is also the beam transmission direction) forms an energy modulation with the seed light wavelength as the period, and the energy modulation forms periodic peaks and troughs.

[0041] In the dispersion section 2, the energy-modulated electron beam is converted into density modulation in the time t direction, such as... Figure 4 As shown, in this embodiment, the dispersion section 2 includes four secondary magnets, wherein the first magnet 201 and the fourth magnet 204 are disposed on the beam path, and the second magnet 202 and the third magnet 203 are disposed between the first magnet 201 and the fourth magnet 204, with the second magnet 202 and the third magnet 203 located on the same side of the beam path. The energy-modulated electron beam has an energy distribution in the time t direction with a period of the seed light wavelength. However, electron beams of different energies take different paths when passing through the dispersion section 2. Figure 4 In the diagram, p-Δp, p, and p+Δp represent the paths taken by electron beams with lower energy, average energy, and higher energy, respectively, in dispersion section 2. Since electron beams of different energies have the same velocity, their different paths (i.e., different transmission distances) will result in different times at their output positions in dispersion section 2. Therefore, electron beams modulated with energy equal to the seed light wavelength will form periodic clusters and micro-beams after passing through dispersion section 2, causing a change in electron beam density along the time t direction. Figure 3 The density changes of the peaks and troughs shown in the figure enable density modulation of the electron beam in the time t direction, and as shown in the figure. Figure 3 As shown, since the length of electron beam 7 in the time t direction is longer than the length of seed light 8, only the part of electron beam 7 that coincides with the time of seed light will be generated into micro-bundles by energy modulation and density modulation.

[0042] After the electron beam enters the radiating section undulator 3, by setting the parameters of the radiating section undulator 3, a certain harmonic component in the micro-beam cluster resonates with the radiating section undulator 3 to generate radiation. The electron beam exchanges energy with the radiation field, resulting in energy loss and a wider energy distribution. This is a well-known technique in the art. In this embodiment, the structure and principle of the radiating section undulator 3 are the same as those of the modulation section undulator 1. The only difference is that in the modulation section undulator 1, the oscillating electron beam exchanges energy with the seed light, while in the radiating section undulator 3, the oscillating electron beam exchanges energy with the radiation field.

[0043] like Figure 5As shown, when the electron beam passes through the microwave deflection cavity 4, viewed from a vertical top-down direction, the microwaves within the cavity exert different deflection forces on the beginning and end of the electron beam along the horizontal X′ direction. Furthermore, the microwave phases are different, resulting in different directions and magnitudes of the forces acting on the electron beam. This causes the incident electron beam 9 to deflect in the horizontal X′ direction, perpendicular to time t (the beam propagation path direction), forming the outgoing electron beam 10. Consequently, the information of the electron beam in the time t direction is transformed into its unfolding along the horizontal X′ direction. When the electron beam passes through the deflection magnet 5 and strikes the beam measurement target 6, as... Figure 7 As shown, electron beams located at different times t are transformed into different positions along the horizontal X-axis of the plane where the beam detection target 6 is located. In this embodiment, the microwaves in the microwave deflection cavity 4 are TM110 mode, which are generated and injected into the microwave deflection cavity 4 by a commercially available microwave generator. In this embodiment, the microwave generator uses a low-level system, a solid-state amplifier, and a klystron to generate and inject microwaves into the microwave deflection cavity 4. The microwave generator can also be other suitable commercial products purchased as needed, as long as it ensures that microwaves of the corresponding frequency are generated and injected into the microwave deflection cavity 4. Figure 6 As shown, in this embodiment, the microwave deflection cavity 4 has a disk-loaded waveguide structure inside. The disk-loaded waveguide structure consists of circular diaphragms 401 with central holes periodically placed inside a smooth circular waveguide 402. The light beam passes through the central holes of each circular diaphragm 401 in sequence. The disk-loaded waveguide structure is a technology known in the art.

[0044] And such Figure 1 As shown, due to the different magnetic stiffness of electrons with different energies, when the electron beam passes through the deflecting magnet 5, the deflection radii of electrons with different energies in the vertical direction are different, thus as... Figure 7 As shown, when the electron beam is fired at the beam measuring target 6, electron beams of different energies are distributed at different positions in the vertical Y direction of the plane where the beam measuring target 6 is located.

[0045] The deflection radius of an electron with energy p under the B0 magnetic field is:

[0046]

[0047] The above formula is a basic physical formula, where p is the electron beam energy, e is the electron beam charge, B0 is the magnetic field strength, and ρ is the electron beam radius.

[0048] The final imaging of the electron beam and seed light on the beam measurement target 6 is as follows: Figure 7As shown, l1 is the centerline of the complete electron beam, and l2 is the centerline of the part where the electron beam and the seed light overlap, which can be regarded as the centerline of the seed light. The distance between l1 and l2 is the deviation Δx, which is used to calculate the relative jitter of the arrival time of the electron beam and the seed light at the target 6. Specifically, Δx multiplied by the time conversion coefficient k is the difference in arrival time between the electron beam and the seed light, that is, the relative arrival time Δt between the electron beam and the seed light.

[0049] Δt=k·Δx (1);

[0050] By monitoring the relative arrival time Δt over a set period of time and calculating the standard deviation, the relative jitter between the arrival times of the electron beam and the seed light can be obtained.

[0051] In equation (1) above, the time conversion coefficient k is obtained by changing the microwave phase Δφ of the microwave deflection cavity 4 and observing the displacement Δx of l1 on the beam target. φ The result was obtained after calculation:

[0052]

[0053] In equation (2) above, f is the microwave frequency of the microwave deflection cavity 4.

[0054] In this embodiment, the deflecting magnet 5 is a diode magnet, and the beam target 5 is a YAG (Y3AL5O12) sheet, which emits fluorescence when it receives an electron beam.

[0055] The working principle of this invention is as follows:

[0056] The electron beam emitted by the free-electron laser device passes sequentially through a modulation undulator 1, a dispersion section 2, a radiation section undulator 3, a microwave deflection cavity 4, and a deflection magnet 5 before striking the beam measurement target 6. In the modulation undulator 1, the electron beam undergoes a gyratory motion and exchanges energy with the seed light, causing the energy p of the electron beam 7 to form a periodic energy modulation with the seed light wavelength along the time t direction (which is also the beam propagation direction) where it coincides with the energy of the seed light 8. This energy modulation creates periodic peaks and troughs. In the dispersion section 2, electron beams of different energies follow different paths during this energy modulation, resulting in periodic clustering of electron beams of different energies. This leads to an increase in the density of the portion of the electron beam coinciding with the seed light along the time t direction. The changes occur, achieving density modulation of the electron beam in the time t direction. After the electron beam enters the undulator 3 in the radiation section, the radiation field is amplified, the electron beam loses energy, and the energy distribution becomes wider. When the electron beam passes through the microwave deflection cavity 4, viewed from a vertical perspective, the microwaves in the microwave deflection cavity 4 apply different deflection forces to the beginning and end of the electron beam in the horizontal direction, and the microwave phases are different. The direction and magnitude of the force on the electron beam are different, thus causing the incident electron beam 9 to be deflected in the horizontal X′ direction perpendicular to the time t direction (the direction of the beam transmission path) to form the outgoing electron beam 10. This transforms the information of the electron beam in the time t direction in the energy modulation section into an expansion along the horizontal X′ direction. Thus, when the electron beam passes through the deflection magnet 5 and hits the beam measurement target 6, as... Figure 7 As shown, electron beams at different times t are then distributed at different positions in the horizontal X direction on the plane of the beam detection target 6. When the electron beams pass through the deflecting magnet 5, due to the different magnetic stiffness of electrons of different energies, the deflection radii of electron beams of different energies after being emitted from the deflecting magnet 5 are different in the vertical direction. Thus, as shown... Figure 7 As shown, when the electron beam strikes the beam measuring target 6, electron beams of different energies are distributed at different positions along the vertical Y-axis of the plane containing the beam measuring target 6. The final image of the electron beam and the seed light on the beam measuring target 6 is as follows: Figure 7 As shown, l1 is the centerline of the complete electron beam, and l2 is the centerline of the part where the electron beam and the seed light overlap, which can also be regarded as the centerline of the seed light. The distance between l1 and l2 is the deviation Δx, which is used to calculate the relative jitter of the arrival time of the electron beam and the seed light to the beam measuring target 6. Specifically, Δx multiplied by the time conversion coefficient k is the difference in arrival time between the electron beam and the seed light, which is the relative arrival time Δt between the electron beam and the seed light. By monitoring the relative arrival time Δt within a set time period and calculating the standard deviation, the relative jitter of the arrival time of the electron beam and the seed light can be obtained.

Claims

1. A method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser, characterized in that: Includes the following steps: Step 1: The electron beam and the seed light are injected into a modulation section undulator (1), and the electron beam oscillates in the modulation section undulator (1). The overlapping part of the electron beam and the seed light along the time t direction forms an energy modulation with the seed light wavelength as the period through energy exchange. Step 2: The electron beam emitted from the modulation section undulator (1) is injected into a dispersion section (2), and electron beams of different energies pass through the dispersion section (2) through different paths and form corresponding periodic clusters to achieve density modulation. Step 3: The electron beam emitted from the dispersion section (2) is injected into a radiation section undulator (3), and the energy distribution of the electron beam becomes wider in the radiation section undulator (3); Step 4: The electron beam emitted from the radiating section undulator (3) is injected into a microwave deflection cavity (4), and when viewed from a vertical perspective, the electron beam is deflected in the horizontal X′ direction perpendicular to the time t direction by the microwaves in the microwave deflection cavity (4). Step 5: The electron beam emitted from the microwave deflection cavity (4) is injected into a deflection magnet (5). Since the magnetic stiffness of electrons with different energies is different, the deflection radius of electrons with different energies after being emitted from the deflection magnet (5) is different in the vertical direction. Step Six: The electron beam emitted by the deflecting magnet (5) is projected onto a target (6), where the centerline of the complete electron beam is l1, the centerline of the part of the electron beam that coincides with the seed light is l2, the distance between l1 and l2 is the deviation Δx, and the relative arrival time Δt between the electron beam and the seed light is: Δt=k·Δx (1); In equation (1) above, k is the time conversion coefficient; Step 7: Monitor the relative arrival time Δt within a set time period and calculate the standard deviation to obtain the relative jitter of the arrival time of the electron beam and the seed light.

2. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 1, characterized in that: The modulation segment undulator (1) includes a plurality of permanent magnets (11) arranged in a straight line, and permanent magnets (11) with opposite polarities are alternately arranged. The electron beam and the seed light pass through each permanent magnet (11) in sequence, and the electron beam undergoes a torsional motion under the action of the alternately arranged permanent magnets (11).

3. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 2, characterized in that: In step one, the electron beam and the seed light interact in the modulation segment undulator (1), where the overlapping part of the electric field strength E>0 of the electron beam and the seed light loses energy and the overlapping part of E<0 gains energy.

4. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 1, characterized in that: The dispersion section (2) includes four secondary magnets, wherein the first magnet (201) and the fourth magnet (204) are located on the beam path, and the second magnet (202) and the third magnet (203) are located between the first magnet (201) and the fourth magnet (204), and the second magnet (202) and the third magnet (203) are located on the same side of the beam path.

5. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 1, characterized in that: In step three, after energy modulation and density modulation, the part of the electron beam that overlaps with the seed light in the time t direction generates a micro-beam cluster. By setting the parameters of the radiation section undulator (3), the first harmonic component in the micro-beam cluster resonates with the radiation section undulator (3) to generate radiation. The electron beam exchanges energy with the radiation field to realize radiation field amplification. The electron beam loses energy and the energy distribution of the electron beam becomes wider.

6. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 1, characterized in that: In step four, the microwave deflection cavity (4) has a disk-loaded waveguide structure inside.

7. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 1, characterized in that: In step five, the deflection radius of an electron with energy p under the B0 magnetic field is: In the above formula, p is the electron beam energy, e is the electron beam charge, B0 is the magnetic field strength, and ρ is the electron beam radius.

8. The method for measuring the arrival time jitter of the electron beam and seed light in a free-electron laser according to claim 1, characterized in that: In step six, the time conversion coefficient k is changed by altering the microwave phase Δφ of the microwave deflection cavity (4) and observing the displacement Δx of l1 on the beam target. φ The result was obtained after calculation: In equation (2) above, f is the microwave frequency of the microwave deflection cavity (4).

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