Methods, apparatus and accelerators for generating gas targets

Abstract

This application provides a method, apparatus, and accelerator for generating a gas target, relating to the field of laser plasma accelerator technology. The method for generating a gas target includes placing a baffle plate at a gas outlet; accelerating a gas target material and ejecting it through the gas outlet to generate an oblique shock wave, thereby forming a gas target; and using a laser pulse to interact with the gas target to form a wake field composed of plasma, resulting in ionization injection, accelerated phase re-phase, and density gradient injection processes. This application captures accelerated electrons during the ionization injection process in the uniform density distribution section of the gas target, extends the acceleration distance by allowing the electron beam, which has reached a deceleration phase, to return to the acceleration phase during the accelerated phase re-phase process in the density rising section of the gas target, and increases the charge and transverse amplitude of the electron beam during the density gradient injection process in the density falling section of the gas target, thereby efficiently increasing the single-emittance number of Betatron X-rays.

Description

Technical Field

[0001] This application relates to the field of laser plasma accelerator technology, and in particular to a method, apparatus and accelerator for generating a gas target. Background Art

[0002] Laser plasma accelerators accelerate electrons by driving a plasma wake field with an acceleration gradient of over 100 megaelectron volts per millimeter in plasma using ultrashort, ultra-intense laser pulses. This accelerates electrons by more than three orders of magnitude compared to traditional accelerators, achieving energy gains of over 100 megaelectron volts within the millimeter scale. Laser plasma accelerators have the potential to significantly reduce the scale and cost of traditional large-scale scientific facilities, and have therefore attracted widespread attention from the scientific and industrial communities.

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

[0004] Currently, Betatron X-ray imaging applications have been extensively and deeply studied. However, due to its low single-emitt number, there are few applications in X-ray near-edge absorption spectroscopy and X-ray Laue diffraction, which have more stringent requirements. Therefore, overcoming the low single-emitt number of existing Betatron X-rays and significantly increasing the single-emitt number of Betatron X-rays is of great significance. Summary of the Invention

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

[0006] The method for generating a gas target provided in this application includes:

[0007] Place the baffle plate above the gas outlet;

[0008] 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, thereby forming a gas target on the side opposite to the gas outlet. The gas target includes a uniform density distribution section, a density rising section and a density falling section in sequence along the propagation direction of the laser pulse.

[0009] By utilizing the interaction between a laser pulse and a gas target, a wake field composed of plasma is formed, generating a high-energy electron beam and Betatron X-rays. The gas target undergoes ionization injection, accelerated complex phase, and density gradient injection processes sequentially along the propagation direction of the laser pulse, corresponding to the density uniform distribution segment, density rising segment, and density falling segment.

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

[0011] Optionally, the gas target material includes a mixture of high-ionization-energy gas and low-ionization-energy gas or a pure high-ionization-energy gas.

[0012] Optionally, the interaction with the gas target to form a wake field composed of plasma also includes:

[0013] In ionization injection, the laser pulse interacts with the gas target 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 continuously accelerates the electrons and emits Betatron X-rays.

[0014] Optionally, using the interaction between a laser pulse and a gas target to form a wake field composed of plasma also includes:

[0015] In the accelerated phase, the electron beam continuously slides in the direction of laser pulse propagation. When the electron beam reaches the deceleration phase, the density rise 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, using the interaction between a laser pulse and a gas target to form a wake field composed of plasma also includes:

[0017] In density gradient injection, the wakefield continuously expands towards the rear end, reducing the phase velocity at the rear end of the wakefield. Electrons with velocities greater than the phase velocity at the rear end of the wakefield are continuously injected into the wakefield after being acted upon, increasing the charge and transverse amplitude of the electron beam and emitting Betatron X-rays.

[0018] This application also provides an apparatus for implementing the above-described method for generating a gas target, characterized in that it comprises:

[0019] A nozzle is used to accelerate a gas target and eject it from a gas outlet.

[0020] A baffle plate is located at the gas outlet.

[0021] Optionally, the nozzle includes:

[0022] Nozzle body;

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

[0024] Optionally, the diameter of the throat is smaller than that of the gas inlet, the diameter of the gas outlet is larger than that of 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] This application also provides an accelerator utilizing a gas target generated by the above method, comprising:

[0026] The accelerator body contains a gas target.

[0027] The laser emitter, installed on the accelerator body, 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 of complex phases, and density gradient injection processes.

[0028] The gas target generation method, apparatus, and accelerator provided in this application capture accelerated electrons through an ionization injection process in the uniform density distribution section of the gas target, and extend the acceleration distance by making the electron beam that has reached the deceleration phase return to the acceleration phase through an acceleration rephase process in the density rising section of the gas target, and increase the charge and transverse amplitude of the electron beam through a density gradient injection process in the density falling section of the gas target, thereby efficiently increasing the number of single photons of Betatron X-rays. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings, without exceeding the scope of protection claimed by this application.

[0030] Figure 1 This is a flowchart illustrating the method for generating the gas target provided in this application;

[0031] Figure 2 A schematic diagram of the apparatus used in the method for generating a gas target;

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

[0033] Figure 4 This is a schematic diagram of the process of ionizing the gas target with a laser pulse to form a wake field composed of plasma.

[0034] Figure 5 This is a schematic diagram of the density distribution of the gas target along the direction of laser pulse propagation when the laser pulse interacts with the gas target;

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

[0036] Figure 7 This is a schematic diagram of density gradient injection.

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

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

[0039] Explanation of reference numerals in the attached figures: 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. Baffle plate; 100. Wake wave field; 200. Electron beam. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a corresponding orientation, or be constructed and operated in a corresponding orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0042] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0043] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

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

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

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

[0047] In step S102, the gas target is accelerated to supersonic speed and ejected through 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 in sequence along the propagation direction of the laser pulse.

[0048] In step S103, the laser pulse interacts with the gas target to form a shape such as Figure 6 The diagram shows a plasma-based wake field 100 that generates a high-energy electron beam and Betatron X-rays. The gas target undergoes sequential reactions along the propagation direction of the laser pulse, as shown below. Figure 5 The diagram shows the ionization injection, accelerated multiphase injection, and density gradient injection processes corresponding to the uniform density distribution segment, the density rising segment, and the density falling segment.

[0049] For example, attached Figure 2As shown, the baffle plate 2 is placed 50 micrometers above the gas outlet 125, and the thickness of the baffle plate 2 is 100 micrometers. The baffle plate 2 is placed horizontally. The gas outlet 125 accelerates and ejects the gas target material vertically from bottom to top. Under the obstruction of the baffle plate 2, the gas target material forms an oblique shock wave on the side opposite to the gas outlet 125, thereby forming a shape such as... Figure 3 The gas target shown has a uniform density distribution section, a density rising section, and a density falling section. The width of the density rising section is approximately 700 micrometers, and the gas back pressure at the gas outlet 125 is 1 MPa. A laser pulse passes sequentially through the uniform density distribution section, the density rising section, and the density falling section of the gas target in a horizontal direction, causing the laser pulse to interact with the gas target.

[0050] By capturing and accelerating electrons through the ionization injection process of laser pulses in the gas target with uniform density distribution, and by accelerating and re-phased through the gas target with increasing density, the electron beam 200, which has reached the deceleration phase, returns to the acceleration phase to extend the acceleration distance. By increasing the charge of the electron beam and increasing the transverse amplitude through the density gradient injection process in the gas target with decreasing density, the number of single photons of Betatron X-rays is efficiently increased.

[0051] As an optional implementation, the gas density in the density uniform distribution section is uniformly distributed, the gas density in the density rising section is greater than the gas density in the density uniform distribution section, and the gas density in the density falling section gradually decreases 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 or a pure high-ionization gas formed by high-ionization energy gas and low-ionization energy gas, such as a helium-nitrogen mixture or pure nitrogen gas.

[0053] For example, a gaseous target material composed of pure nitrogen is accelerated and ejected onto a blocking plate 2 to form a gaseous target composed of nitrogen atoms with a uniform density distribution section, a density rising section, and a density falling section.

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

[0055] In sub-step S131, the ionized laser pulse interacts with the gas target to generate electrons. The electrons are captured by the wake field 100 through ionization injection to form an electron beam 200, which in turn continuously accelerates the electrons and radiates Betatron X-rays.

[0056] For example, such as Figure 6 As shown, a laser pulse ionizes a gas target composed of nitrogen atoms to form a wake field 100 composed of plasma, with the inner layer of nitrogen atoms containing N atoms. 6+ and N7+ Electrons, after passing through the wake field 100, are captured by the wake field 100 through ionization injection to form an electron beam 200, and then N... 6+ and N 7+ Electrons are continuously accelerated and emit 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 accelerating and reconstituted electron beam 200 continuously slides towards the front end of the sheath of the wake field 100, i.e., the propagation direction of the laser pulse. When the electron beam 200 reaches the deceleration phase, the density rise section of the gas target is introduced so that the electron beam 200 returns to the acceleration phase, realizing accelerated reconstitution, thereby extending the acceleration distance of the electron beam 200, and ultimately increasing the energy and transverse oscillation cycle number 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, as follows Figure 7 As shown, the wake field 100 injected with density gradient continuously expands towards the rear end, reducing the phase velocity at the rear end of the wake field 100. Electrons with velocities greater than the phase velocity at the rear end of the wake field 100 are continuously injected into the wake field 100 after being acted upon, increasing the charge of the electron beam 200 and radiating Betatron X-rays. At the same time, the lateral focusing force of the wake field 100 decreases, increasing the lateral amplitude of the electron beam 200.

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

[0062] Among them, a Mach-Zehnder interferometer can be selected. The plasma density distribution at 750 micrometers above the gas outlet 125 is measured using the Mach-Zehnder interferometer, thereby obtaining... Figure 3 The diagram shows the plasma density distribution.

[0063] This application also provides an apparatus for implementing the above-described method for generating a gas target, characterized in that it includes a nozzle 1 and a baffle 2. The nozzle 1 is used to accelerate the gas target material and eject it from a gas outlet 125. The baffle 2 is located at the gas outlet 125, and the baffle 2 may be positioned with a gap or in contact with the gas outlet 125.

[0064] Among them, the baffle plate 2 is parallel or approximately parallel to the gas outlet 125, and the baffle plate 2 can be made of a rigid material, such as a thin metal sheet.

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

[0066] refer to Figure 8 As an optional implementation, the diameter of the throat 123 is smaller than that of the gas inlet 121, the diameter of the gas outlet 125 is larger than that of 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. The gas target is accelerated to supersonic speed through the gas compression section 122 and the gas expansion section 124, and then ejected from the gas outlet 125.

[0068] This application also provides an accelerator utilizing plasma generated by the above method, including an accelerator body and a laser emitter. The accelerator body contains a gas target, and the laser emitter is mounted on the accelerator body for emitting laser pulses. The laser pulses propagate sequentially through a density uniform distribution section, a density rising section, and a density falling section of the gas target, interacting with the gas target. At the density uniform distribution section, the density rising section, and the density falling section, corresponding physical processes of ionization injection, accelerated complex phase, and density gradient injection occur, respectively.

[0069] like Figure 9 As shown, using the accelerator with the aforementioned plasma density distribution provided in this application, the laser pulse energy used in the experiment was 0.9 joules, the pulse width was 37 femtoseconds, and the full width at half maximum (FWHM) of the focal diameter was 16 micrometers. Based on the gas target and plasma density distribution in this accelerator, the number of Betatron X-ray single emitters produced was 0.8 × 10⁻⁶. 10 (Average of 10 emission units), the single-photon flux exceeds 5 × 10⁻⁶ in the energy range of 0.1 kEV to 2 kEV. 6 With a bandwidth of one-thousandth of a photon, it is known to be tens of times higher than existing technologies, 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 this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for generating a gas target, characterized in that, include: Place the baffle plate above 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, thereby forming a gas target on the side of the blocking plate opposite to the gas outlet. The gas target includes a uniform density distribution section, a density rising section and a density falling 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 generates a high-energy electron beam and Betatron X-rays. The gas target undergoes ionization injection, accelerated complex phase injection and density gradient injection processes in sequence along the propagation direction of the laser pulse, corresponding to the density uniform distribution segment, the density rising segment and the density falling segment.

2. The method according to claim 1, characterized in that, The gas density is uniformly distributed in the density uniform distribution section, the gas density in the density rising section is greater than the gas density in the density uniform distribution section, and the gas density in the density falling section gradually decreases 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 or a pure high-ionization gas composed of high-ionization energy gas and low-ionization energy gas.

4. The method according to claim 1, characterized in that, The formation of a wake field composed of plasma by interacting the laser pulse with the gas target 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 in turn continuously accelerates the electrons and radiates the Betatron X-rays.

5. The method according to claim 4, characterized in that, The process of generating a wake field composed of plasma by interacting the laser pulse with the gas target further includes: In the accelerated phase, the electron beam continuously slides in the propagation direction of the laser pulse. When the electron beam reaches the deceleration phase, the density rise 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 process of generating a wake field composed of plasma by interacting the laser pulse with the gas target further includes: In the density gradient injection, the wake field continuously expands towards the rear end, reducing the phase velocity at the rear end of the wake field. Electrons with velocities greater than the rear end phase velocity of the wake field are continuously injected into the wake field after being acted upon, thereby increasing the charge and transverse amplitude of the electron beam and radiating the Betatron X-rays.

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

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

9. The apparatus according to claim 8, characterized in that, The diameter of the throat is smaller than that of the gas inlet, the diameter of the gas outlet is larger than that of 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 utilizing a gas target generated by the method of any one of claims 1-6, characterized in that, include: An accelerator body, wherein the gas target is located within the accelerator body; A laser emitter, mounted on the accelerator body, is used to emit laser pulses. The laser pulses pass through the gas target along the propagation direction and interact with it to induce ionization injection, accelerated complex phase, and density gradient injection processes.

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