Gas target generation method and device and accelerator

Abstract

The invention provides a gas target generation method and device and an accelerator, and relates to the technical field of laser plasma accelerators. The gas target generation method provided by the invention comprises the following steps: placing a blocking sheet at a gas outlet; the gas target material is accelerated and sprayed out through a gas outlet so as to generate oblique shock waves, and then a gas target is formed; the laser pulse and the gas target act to form a tail wave field formed by plasma, ionization injection is carried out, and the complex phase and density gradient injection process is accelerated. Accelerating electrons are captured in the ionization injection process in the gas target density uniform distribution section, and electron beams reaching the deceleration phase return to the acceleration phase again through the acceleration multiphase process in the density rising section of the gas target, so that the acceleration distance is prolonged; through the density gradient injection process in the gas target density descending section, the charge quantity of electron beams is increased, the transverse amplitude is increased, and the number of single luminous photons of the Betatron X-rays is further efficiently increased.

Description

Technical Field

[0001] The present application relates to the technical field of laser plasma accelerators, and in particular to a method and device for generating a gas target and an accelerator. Background Art

[0002] Laser plasma accelerators use ultrashort and ultra-intense laser pulses to drive a plasma wakefield with an acceleration gradient of more than 100 mega-electron-volts per millimeter in the plasma to accelerate electrons. This makes the acceleration effect three orders of magnitude greater than that of traditional accelerators, and energy gains of more than 100 mega-electron-volts can be achieved within the millimeter scale. Laser plasma accelerators have the potential to significantly reduce the scale and cost of traditional large-scale scientific facilities using light sources, and therefore have received widespread attention from the scientific and industrial communities.

[0003] The ultrafast high-brightness Betatron X-ray source driven by a laser plasma accelerator (laser plasma accelerator self-generated synchrotron radiation source) is the self-generated radiation of the laser plasma accelerator. It has good peak brightness, micron-level source size and femtosecond pulse length. It has great application prospects in research fields such as ultrahigh resolution imaging, ultrafast X-ray near-edge absorption spectroscopy and ultrafast X-ray Laue diffraction.

[0004] At present, imaging applications based on Betatron X-rays have been widely and deeply studied, but due to its low single-photon number, it is rarely used in the more demanding X-ray near-edge absorption spectrum and X-ray Laue diffraction. Therefore, it is of great significance to overcome the low single-photon number of existing Betatron X-rays and significantly increase the single-photon number of Betatron X-rays. Summary of the invention

[0005] Based on this, the present application provides a method, device and accelerator for generating a gas target to efficiently increase the number of single-emission photons of Betatron X-rays.

[0006] The method for generating a gas target provided in the present application comprises:

[0007] Place a blocking sheet over the gas outlet;

[0008] The gas target is accelerated to supersonic speed and ejected through the gas outlet, and the blocking plate blocks the ejected gas target to generate an oblique shock wave, thereby forming a gas target on the side of the blocking plate opposite to the gas outlet, and the gas target includes a uniform density distribution section, a density increase section and a density decrease section in sequence along the propagation direction of the laser pulse;

[0009] The laser pulse interacts with the gas target to form a wake field composed of plasma, and generate high-energy electron beams and Betatron X-rays. The gas target undergoes ionization injection, acceleration rephase and density gradient injection processes corresponding to the uniform density distribution section, density increase section and density decrease section along the propagation direction of the laser pulse.

[0010] Optionally, the gas density in the uniform density distribution section is uniformly distributed, the gas density in the density rising section is greater than the gas density in the uniform density distribution section, and the gas density in the density falling section gradually decreases starting from the gas density at the output end of the density rising section.

[0011] Optionally, the gas target material includes a mixed gas formed by a high ionization energy gas and a low ionization energy gas or a pure high ionization energy gas.

[0012] Optionally, the step of acting with the gas target to form a wake field composed of plasma further comprises:

[0013] In ionization injection, laser pulses interact with gas targets to generate electrons and form a wake field. The electrons are captured by the wake field through ionization injection to form an electron beam, which then causes the electrons to be continuously accelerated and radiate Betatron X-rays.

[0014] Optionally, utilizing the laser pulse to interact with the gas target to form a wake field composed of plasma further includes:

[0015] In the acceleration phase, the electron beam continuously slides in the propagation direction of the laser pulse. When the electron beam reaches the deceleration phase, the density increase section of the gas target is introduced to make the electron beam return to the acceleration phase, thereby extending the acceleration distance of the electron beam.

[0016] Optionally, utilizing the laser pulse to interact with the gas target to form a wake field composed of plasma further includes:

[0017] In density gradient injection, the wake field continues to expand toward the rear end, and the rear end phase velocity of the wake field decreases. After being acted upon by the wake field, electrons whose velocities are greater than the rear end phase velocity of the wake field are continuously injected into the wake field, increasing the charge and transverse amplitude of the electron beam and radiating Betatron X-rays.

[0018] The present application also provides a device for implementing the above-mentioned method for generating a gas target, characterized in that it includes:

[0019] a nozzle, used to accelerate the gas target and eject it from the gas outlet;

[0020] The blocking plate is located at the gas outlet.

[0021] Optionally, the nozzle comprises:

[0022] Nozzle body;

[0023] The gas passage is opened inside the nozzle body and includes a gas inlet, a gas compression section, a throat, a gas expansion section and a gas outlet in sequence along the conveying direction of the gas target.

[0024] Optionally, the diameter of the throat is smaller than the gas inlet, the diameter of the gas outlet is larger than the throat, the diameter of the gas compression section decreases along the conveying direction of the gas target, and the diameter of the gas expansion section increases along the conveying direction of the gas target.

[0025] The present application also provides an accelerator using a gas target generated by the above method, comprising:

[0026] An accelerator body, wherein the accelerator body has a gas target;

[0027] The laser emitter is installed in the accelerator body and is used to emit laser pulses. The laser pulses pass through the gas target along the propagation direction and interact with it to cause ionization injection, acceleration rephase and density gradient injection processes.

[0028] The gas target generation method, device and accelerator provided in the present application capture accelerated electrons through the ionization injection process in the gas target density uniform distribution section, return the electron beam that has reached the deceleration phase to the acceleration phase through the acceleration rephase process in the gas target density rising section to extend the acceleration distance, and increase the charge amount of the electron beam and the lateral amplitude through the density gradient injection process in the gas target density falling section, thereby efficiently improving the number of single photons of Betatron X-rays. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without exceeding the scope of protection required by the present application.

[0030] Figure 1 It is a schematic flow chart of a method for generating a gas target provided by the present application;

[0031] Figure 2 A schematic structural diagram of a device for a method of generating a gas target;

[0032] Figure 3 is a schematic diagram of the density distribution of plasma along the longitudinal direction;

[0033] Figure 4 The present invention is a schematic flow diagram of a process of making a laser pulse ionize the gas target to form a wake field composed of plasma;

[0034] Figure 5 It is a schematic diagram of the density distribution of the gas target along the propagation direction of the laser pulse when the laser pulse acts on the gas target;

[0035] Figure 6 This is a schematic diagram of the work of the wake field capturing electrons during the ionization injection process;

[0036] Figure 7 It is a working schematic diagram of density gradient injection;

[0037] Figure 8 It is a schematic diagram of the structure of the nozzle;

[0038] Fig. 9 It is a single-shot spectrum of Betatron X-rays obtained using the accelerator provided by this application.

[0039] Explanation of the reference numerals: 1. nozzle; 11. nozzle body; 12. gas passage; 121. gas inlet; 122. gas compression section; 123. throat; 124. gas expansion section; 125. gas outlet; 2. blocking plate; 100. wake field; 200. electron beam. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0041] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a corresponding orientation, be constructed and operated in a corresponding orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present application, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0042] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0044] It should be noted that, for ease of understanding, in the present application, the propagation direction of the laser pulse is set as the front end, and the direction opposite to the propagation direction of the laser pulse is set as the back end.

[0045] refer to Figure 1 The method for generating a gas target provided in the present application includes steps S101-S103.

[0046] In step S101 , the blocking sheet 2 is placed above the gas outlet 125 .

[0047] In step S102, the gas target is accelerated to supersonic speed and ejected through the gas outlet 125. The blocking plate 2 blocks the ejected gas target to generate an oblique shock wave, thereby forming a gas target on the side of the blocking plate 2 opposite to the gas outlet 125. The gas target includes a uniform density distribution section, a density rising section, and a density falling section along the propagation direction of the laser pulse.

[0048] In step S103, the laser pulse interacts with the gas target to form Figure 6 The tail wave field 100 composed of plasma is shown, and high-energy electron beam and Betatron X-ray are generated. The gas target is sequentially generated along the propagation direction of the laser pulse as follows: Figure 5 The ionization injection, accelerated multiphase and density gradient injection processes corresponding to the density uniform distribution section, density rising section and density falling section are shown.

[0049] For example, Figure 2As shown in FIG. 1 , the barrier sheet 2 is placed 50 microns above the gas outlet 125, and the thickness of the barrier sheet 2 is 100 microns. The barrier sheet 2 is placed in a horizontal direction. The gas outlet 125 accelerates and ejects the gas target from bottom to top in the vertical direction. The gas target is blocked by the barrier sheet 2 to form an oblique shock wave on the side of the barrier sheet 2 opposite to the gas outlet 125, thereby forming a gas having the following characteristics: Figure 3 The gas target with uniform density distribution section, density rising section and density falling section is shown, wherein the width of the density rising section is about 700 microns, and the gas back pressure at the gas outlet 125 is 1 MPa. The laser pulse passes through the uniform density distribution section, density rising section and density falling section of the gas target in the horizontal direction in sequence, so that the laser pulse acts on the gas target.

[0050] Accelerated electrons are captured by the ionization injection process of the laser pulse in the uniformly distributed density section of the gas target, and the electron beam 200 that has reached the deceleration phase is returned to the acceleration phase through the acceleration rephase process in the density rising section of the gas target to extend the acceleration distance. The charge amount of the electron beam and the lateral amplitude are increased through the density gradient injection process in the density falling section of the gas target, thereby effectively improving the number of single photons of the Betatron X-ray.

[0051] As an optional implementation, the gas density in the uniform density distribution section is uniformly distributed, the gas density in the density rising section is greater than the gas density in the uniform density distribution section, and the gas density in the density falling section gradually decreases starting from the gas density at the output end of the density rising section.

[0052] As an optional implementation, the gas target material includes a mixed gas formed by a high ionization energy gas and a low ionization energy gas or a pure high ionization energy gas, such as a helium-nitrogen mixed gas or pure nitrogen.

[0053] For example, a gas target composed of pure nitrogen is accelerated and ejected to the blocking plate 2 to form a gas target composed of nitrogen atoms having a uniform density distribution section, a density increase section, and a density decrease section.

[0054] refer to Figure 4 As an optional implementation, step S103 includes sub-step S131.

[0055] In sub-step S131 , the laser pulse of ionization injection acts on the gas target to generate electrons, and the electrons are captured by the wake field 100 through ionization injection to form an electron beam 200 , and then the electrons are continuously accelerated and radiate Betatron X-rays.

[0056] For example, Figure 6 As shown, a gas target composed of nitrogen atoms is ionized by a laser pulse to form a wake field 100 composed of plasma. 6+ and N7+ The electrons are captured by the wake field 100 through ionization injection to form an electron beam 200, and then N 6+ and N 7+ The electrons are continuously accelerated and radiate Betatron X-rays.

[0057] refer to Figure 4 As an optional implementation, step S103 also includes sub-step S132.

[0058] In sub-step S132, the electron beam 200 in the accelerated rephase continuously slides toward the front end of the sheath of the wake field 100, that is, the propagation direction of the laser pulse. When the electron beam 200 reaches the deceleration phase, the density rising section of the gas target is introduced to make the electron beam 200 return to the acceleration phase, realizing the accelerated rephase, thereby extending the acceleration distance of the electron beam 200, and ultimately increasing the energy and the number of transverse oscillation cycles of the electron beam 200.

[0059] refer to Figure 4 As an optional implementation, step S103 also includes sub-step S133.

[0060] In sub-step S133, if Figure 7 As shown, the wake field 100 injected by the density gradient continues to expand toward the rear end, and the rear end phase velocity of the wake field 100 is reduced. After the wake field 100 acts, electrons with a velocity greater than the rear end phase velocity of the wake field 100 are continuously injected into the wake field 100, so that the charge of the electron beam 200 increases and Betatron X-rays are radiated. At the same time, the lateral focusing force of the wake field 100 is reduced, so that the lateral amplitude of the electron beam 200 increases.

[0061] refer to Figure 1 As an optional embodiment, the method for generating a gas target further includes detecting the plasma density distribution of the gas target formed above the gas outlet 125 by an interferometer to determine the plasma density distribution state.

[0062] The interferometer may be a Mach-Zehnder interferometer, and the plasma density distribution at 750 μm above the gas outlet 125 is measured by the Mach-Zehnder interferometer to obtain the following: Figure 3 Schematic diagram of plasma density distribution is shown.

[0063] The present application also provides a device for implementing the above-mentioned method for generating a gas target, characterized in that it includes a nozzle 1 and a blocking plate 2. The nozzle 1 is used to accelerate the gas target material and eject it from the gas outlet 125. The blocking plate 2 is located at the gas outlet 125, and the blocking plate 2 can be spaced apart from the gas outlet 125 or placed in contact with the gas outlet 125.

[0064] The blocking sheet 2 is parallel or approximately parallel to the gas outlet 125 , and the blocking sheet 2 can be made of a hard material, such as a metal sheet.

[0065] refer to Figure 2 and Figure 8 As an optional embodiment, the nozzle 1 includes a nozzle body 11 and a gas passage 12. The gas passage 12 is opened inside the nozzle body 11, and includes a gas inlet 121, a gas compression section 122, a throat 123, a gas expansion section 124 and a gas outlet 125 in sequence along the delivery direction of the gas target.

[0066] refer to Figure 8 As an optional embodiment, the diameter of the throat 123 is smaller than the gas inlet 121, the diameter of the gas outlet 125 is larger than the throat 123, the diameter of the gas compression section 122 decreases along the conveying direction of the gas target, and the diameter of the gas expansion section 124 increases along the conveying direction of the gas target.

[0067] The gas target is introduced through the gas inlet 121 , and the gas target is accelerated by the gas compression section 122 and the gas expansion section 124 to increase its speed to supersonic speed, and is ejected from the gas outlet 125 .

[0068] The present application also provides an accelerator using the plasma generated by the above method, including an accelerator body and a laser emitter. The accelerator body has a gas target, and the laser emitter is installed on the accelerator body for emitting laser pulses, which pass through the uniform density distribution section, density rise section and density drop section of the gas target in the propagation direction, and interact with the gas target, and the corresponding physical processes of ionization injection, accelerated phase recombination and density gradient injection occur in the uniform density distribution section, density rise section and density drop section respectively.

[0069] like Fig. 9 As shown, the accelerator provided by the present application with the above plasma density distribution is used, and the laser pulse energy used in the experiment is 0.9 joules, the pulse width is 37 femtoseconds, and the half-maximum full width of the focus diameter is 16 microns. Based on the gas target and plasma density distribution in the accelerator, the number of single photons of Betatron X-rays generated is 0.8×10 10 (10 shots average), the single photon flux in the energy range of 0.1 keV to 2 keV exceeds 5×10 6 With a photon bandwidth of one thousandth, it can be seen that it is dozens of times higher than the existing technology, thus meeting the application requirements of ultra-high signal-to-noise ratio single-shot imaging, ultrafast X-ray near-edge absorption spectroscopy, and ultrafast X-ray Laue diffraction.

[0070] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application. At the same time, changes or deformations made by those skilled in the art based on the ideas of the present application, the specific implementation methods and the scope of application of the present application, all belong to the scope of protection of the present application. In summary, the content of this specification should not be construed as a limitation on the present application.

Claims

1. A method for generating a gas target, characterized in that: include: Place a blocking sheet over the gas outlet; The gas target is accelerated to supersonic speed and ejected through the gas outlet, the blocking plate blocks the ejected gas target to generate an oblique shock wave, and then a gas target is formed on the side of the blocking plate opposite to the gas outlet, and the gas target includes a uniform density distribution section, a density increase section and a density decrease section in sequence along the propagation direction of the laser pulse; The laser pulse interacts with the gas target to form a wake field composed of plasma, and generate a high-energy electron beam and Betatron X-rays. The gas target sequentially undergoes ionization injection, accelerated multiphase and density gradient injection processes corresponding to the uniform density distribution section, the density rising section and the density falling section along the propagation direction of the laser pulse.

2. The method according to claim 1, characterized in that The gas density in the uniform density distribution section is uniformly distributed, the gas density in the density rising section is greater than the gas density in the uniform density distribution section, and the gas density in the density falling section gradually decreases starting from the gas density at the output end of the density rising section.

3. The method according to claim 1, characterized in that The gas target material includes a mixed gas formed by a high ionization energy gas and a low ionization energy gas or a pure high ionization energy gas.

4. The method according to claim 1, characterized in that: The method of utilizing the laser pulse to interact with the gas target to form a wake field composed of plasma includes: In the ionization injection, the laser pulse interacts with the gas target to generate electrons and form the wake field. The electrons are captured by the wake field through ionization injection to form an electron beam, which then causes the electrons to be continuously accelerated and radiate the Betatron X-rays.

5. The method according to claim 4, characterized in that The method of utilizing the laser pulse to interact with the gas target to form a wake field composed of plasma further comprises: In the acceleration complex phase, the electron beam continuously slides in the propagation direction of the laser pulse. When the electron beam reaches the deceleration phase, the density increase section of the gas target is introduced to make the electron beam return to the acceleration phase, thereby extending the acceleration distance of the electron beam.

6. The method according to claim 4, characterized in that The method of utilizing the laser pulse to interact with the gas target to form a wake field composed of plasma further comprises: During the density gradient injection, the wake field continues to expand toward the rear end, and the rear end phase velocity of the wake field is reduced. After being acted upon by the wake field, electrons whose velocity is greater than the rear end phase velocity of the wake field are continuously injected into the wake field, so that the charge amount and the transverse amplitude of the electron beam are increased, and the Betatron X-rays are radiated.

7. A device for implementing the method for generating a gas target according to any one of claims 1 to 6, characterized in that: include: A nozzle, used to accelerate the gas target and eject it from a gas outlet; A blocking sheet is located at the gas outlet.

8. The device according to claim 7, characterized in that The nozzle comprises: Nozzle body; The gas passage is opened inside the nozzle body and includes a gas inlet, a gas compression section, a throat, a gas expansion section and the gas outlet in sequence along the conveying direction of the gas target.

9. The device according to claim 8, characterized in that The diameter of the throat is smaller than the gas inlet, the diameter of the gas outlet is larger than the throat, the diameter of the gas compression section decreases along the conveying direction of the gas target, and the diameter of the gas expansion section increases along the conveying direction of the gas target.

10. An accelerator using a gas target generated by the method according to any one of claims 1 to 6, characterized in that: include: An accelerator body, wherein the gas target is disposed inside the accelerator body; The laser emitter is installed on the accelerator body and is used to emit laser pulses. The laser pulses pass through the gas target along the propagation direction and interact with the gas target to cause ionization injection, accelerated phase regeneration and density gradient injection processes.

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