Gas shock wave generator for laser wakefield electron accelerator

Abstract

A gas shock wave generating device for a laser wakefield accelerator comprises: a vacuum six-dimensional electrically controlled translation stage, a high-speed solenoid valve, a solenoid valve controller, a solenoid valve bracket, a gas flow stabilizing tube, a trapezoidal obstacle, and a gas storage tank. The present invention effectively provides a suitable gas shock wave for a laser wakefield accelerator. It has the advantages of simple structure, ease of use, flexible adjustment, high precision, and stability and reliability. The present invention is mainly used in laser wakefield accelerators, providing a plasma distribution with a sharp change in density for laser wakefield electron accelerators, and can adjust the required gas density and shock wave position and other parameters according to the laser conditions. Compared with traditional devices such as gas pools and capillaries, the present invention can obtain high-quality, highly stable electron beams through very steep density changes.

Description

Technical Field

[0001] The present invention is a device for generating special gas density distribution suitable for the field of ultra-strong and ultra-short laser-matter interaction, and relates to a laser wakefield electron accelerator based on density gradient injection, in particular, a gas shock wave generating device that is easy to control and stable, which is of great value in realizing the laser wakefield accelerator to generate a stable electron beam with high energy, high current and low energy dispersion. Background Art

[0002] With the widespread application demand for high-energy electron beams, the disadvantages of traditional linear electron accelerators, such as high cost and large footprint, have gradually become apparent. However, the low price and small size of laser wakefield electron accelerators have enabled this field to develop rapidly. The key device required to generate gas distribution requires a new design to meet the needs of special gases, high-precision adjustment, and high stability.

[0003] Laser wakefield electron accelerators have a variety of injection mechanisms, including self-injection, ionization injection, density gradient injection, laser collision injection, etc., among which density gradient injection utilizes the phase velocity difference of the wakefield at the steep plasma density drop to inject background electrons into the bubble. This method can easily produce high-quality electron beams with low energy dispersion and low emissivity (reference A.Buck Phys.Rev.Lett.110,185006), and this injection method does not rely on the mixing of multiple gases or the pre-ionization of gases. The device is simple in experiment and easy to implement. Therefore, this injection method has been widely studied and applied in South Korea, the United States, Europe and other parts of the world (reference K.Schmid Phys.Rev.STAccel.Beams13,091301), and there are experimental results of producing high-quality electron beams by larger density gradients (reference K.Kim Journal of the Korean Physical Society, Vol.73,No.5,September2018). Previous research and inventions relied on blade-shaped gas pools to generate gas density gradients. However, these traditional blade-shaped gas pools are simple in structure, produce unstable bow shocks, and have difficulty adjusting the gas density distribution. Furthermore, they are difficult to align with the laser beam. To meet application requirements, the experiment required a gas shock structure with strong stability, controllable gas density distribution, simple adjustment, and convenient operation, while ensuring synchronization with the laser beam. Summary of the Invention

[0004] The object of the present invention is to provide a gas shock wave generating device for a laser wakefield electron accelerator. The device can generate an oblique shock wave with a very large density gradient on one side and a stable gas density distribution of a free jet on the other side for the laser wakefield electron accelerator. The device can also accurately adjust the spatial position of the entire gas structure, the relative position of the shock wave and the gas density and gas type, and can also control the gas ejection synchronously with the laser signal.

[0005] The technical solutions of the present invention are as follows:

[0006] A gas shock wave generating device for a laser wakefield electron accelerator is characterized in that its structure includes: a vacuum six-dimensional electrically controlled translation stage, a high-speed electromagnetic valve, an electromagnetic valve controller, an electromagnetic valve bracket, a gas flow stabilizing tube, a trapezoidal obstacle, and a gas storage tank; the vacuum six-dimensional electrically controlled translation stage can be used in a vacuum and can be controlled by an external controller or a computer to move the entire stage forward, backward, left, and right, as well as to lengthen and shorten the relative distance between the upper and lower parts in six adjustment dimensions; there is a screw hole just above the translation stage, and screws and the translation stage are fixed below the trapezoidal obstacle; a transparent small hole is opened on the side of the trapezoidal obstacle to allow the laser to pass through; the electromagnetic valve bracket is fixed to the side of the translation stage by screws, and the electromagnetic valve bracket is connected to the high-speed electromagnetic The valves are connected by screws, so that the high-speed solenoid valve is indirectly fixed on the six-dimensional translation stage, and its position can be adjusted by the six-dimensional translation stage; the gas flow stabilizing tube is fixed by screws at the outlet of the high-speed solenoid valve, and the top side of the flow stabilizing tube is threaded and fixed to the outlet of the solenoid valve, and the trapezoidal obstacle is directly below the outlet of the gas flow stabilizing tube and at a certain distance from the flow stabilizing tube; the inlet of the high-speed solenoid valve is connected to the external gas storage tank by a metal gas pipe to ensure air tightness; the high-speed solenoid valve is connected to the solenoid valve controller by a wire to control the switch of the solenoid valve, and the signal of the controller is triggered by the laser signal to ensure that the gas shock wave has been generated and is stable when the laser reaches the obstacle.

[0007] The relative distance between the trapezoidal obstacle and the gas flow stabilizing tube can be adjusted with micron precision by the six-dimensional translation stage to control the relative spatial position of the gas shock wave.

[0008] The signal sending time of the solenoid valve controller can be adjusted with microsecond accuracy relative to the laser arrival time, so that the laser can reach the trapezoidal obstacle at different times after the high-speed solenoid valve is opened.

[0009] The trapezoidal obstacle is trapezoidal in both side sections, with the small holes thereon crossing the narrower section, and the material can be metal or ceramic.

[0010] The inner diameter of the gas flow stabilizing tube is consistent with the inner diameter of the outlet of the high-speed solenoid valve, and is made of a high-hardness organic polymer material.

[0011] The external gas storage tank can be pre-filled with a single-component gas or a mixed multi-component gas, and its output pressure can be continuously adjusted from 0 psi to 200 psi.

[0012] The six-dimensional electric-controlled translation stage and the high-speed electromagnetic valve are made of metal materials and can be used in a vacuum environment.

[0013] Compared with previous inventions, the present invention has the following features and effects:

[0014] 1. The present invention uses the trapezoidal obstacle to generate an oblique shock wave at the free jet outlet, which has better application performance in the laser wakefield electron accelerator.

[0015] 2. The gas flow stabilizing tube can effectively overcome the various instabilities brought about by supersonic airflow. Compared with the previous gas pool, the present invention has better stability, and the open structure makes the life of the device longer.

[0016] 3. The present invention has multiple adjustment dimensions, which can not only adjust the overall position, but also adjust the relative distance between the upper and lower parts, with high flexibility and rich functions.

[0017] 4. The present invention utilizes small holes on the obstacle to ensure that the ultra-strong and ultra-short laser passes through in a vertical direction, thereby reducing the instability of the experimental results caused by the laser pointing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of a gas shock wave generating device of the laser wakefield electron accelerator of the present invention.

[0019] Figure 2 This is a CCD real picture of the gas shock wave generating device of the laser wakefield electron accelerator of the present invention, and the shock wave is in the frame.

[0020] Figure 3 This is a schematic diagram of the gas density distribution near the outlet of the gas steady flow tube simulated by the gas shock wave generating device of the laser wakefield electron accelerator of the present invention, wherein the white line is the direction of the ultra-strong and ultra-short laser transmission axis.

[0021] Figure 4 It is a schematic curve of the gas density distribution along the laser transmission axis of the gas shock wave generating device of the laser wakefield electron accelerator obtained by simulation. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention should not be limited thereto.

[0023] See also Figure 1 , Figure 1This is a schematic diagram of the gas shock wave structure generating device of the laser wakefield electron accelerator of the present invention. As can be seen from the figure, the present invention comprises: a vacuum six-dimensional electrically controlled translation stage 5, a high-speed electromagnetic valve 2, an electromagnetic valve controller 8, an electromagnetic valve bracket 7, a gas flow stabilizing tube 3, a trapezoidal obstacle 4, and a gas storage tank 6; the lower end of the vacuum six-dimensional electrically controlled translation stage 5 is square, and is divided into two layers, the top surface of the upper layer has screw holes for fixing the trapezoidal obstacle 4, and the side surface of the lower layer has screw holes for fixing the electromagnetic valve bracket 7, which can be adjusted up and down and left and right as a whole so that the ultra-strong ultra-short laser 1 just passes through the small hole 11 of the trapezoidal obstacle 4, and at the same time, the distance between the upper and lower layers can be adjusted to change the distance between the gas flow stabilizing tube 3 and the trapezoidal obstacle 4; the electromagnetic valve controller 8 sends a signal through the laser to control the switch of the high-speed electromagnetic valve 2 so that the gas is moved before the ultra-strong ultra-short laser 1 reaches the trapezoidal obstacle 4 After being ejected for a sufficiently long time, the gas from the gas tank 6 reaches the inlet 2-1 of the high-speed solenoid valve 2, passes through the high-speed solenoid valve 2, the solenoid valve outlet 2-2 and the gas flow stabilizing tube 3, and is ejected; since the ejected gas is supersonic, the ejected gas will form an inclined shock wave on the trapezoidal obstacle 3, and then the ultra-strong ultrashort laser 1 enters from the left side of the small hole 11 on the obstacle and exits from the right side, interacting with the formed gas structure; since the gas type and gas pressure of the external gas tank 6 can be adjusted, and the distance between the gas flow stabilizing tube 6 and the trapezoidal obstacle 4 can be adjusted, the relative position of the shock wave, the intensity of the shock wave, and the density of the gas can be adjusted, thereby adjusting the result of the interaction between the ultra-strong ultrashort laser 1 and the gas structure.

[0024] The present invention can be applied to the generation of gas shock waves in a laser wakefield electron accelerator, and the operation process is as follows:

[0025] First, based on the CCD imaging of the side of the present invention, the upper and lower spacing between the trapezoidal obstacle 4 and the gas steady flow tube 3 and the placement position are determined so that the small hole 11 on it is perpendicular to the propagation direction of the ultra-strong ultrashort laser 1. Then, according to the state of the ultra-strong ultrashort laser 1 after passing through the small hole 11, the up, down, left and right positions of the vacuum six-dimensional electric-controlled translation stage 5 are fine-tuned so that the ultra-strong ultrashort laser 1 passes through the small hole 11 completely; next, by measuring the time when the solenoid valve controller 8 receives the laser signal and the time when the laser reaches the trapezoidal obstacle 4, the time delay required for the solenoid valve controller 8 to control the opening of the high-speed solenoid valve 2 is determined; after the delay is set, the inlet 2-1 of the high-speed solenoid valve 2 is connected to the gas tank 6. The external gas tank 6 is pre-filled with the required type of high-pressure gas and has a pressure reducing valve on it to control the pressure of the ejected gas.

[0026] The present invention generates a special gas structure with a shock wave based on the principle that a supersonic airflow will form an oblique shock wave when encountering a sharp obstacle. The half-apex angle of the shock wave and the Mach number of the airflow can be calculated by the following formula: μ is the half-apex angle of the shock wave, and M is the Mach number of the gas.

[0027]

[0028] After computational fluid dynamics simulation of compressible fluid, Figure 3 It can be clearly seen that the gas has formed an inclined shock wave behind the trapezoidal obstacle 4, and the density distribution diagram on the white line is as follows: Figure 4 The very steep density changes caused by the gas shock wave can be seen more intuitively, forming a special gas density distribution.

[0029] Figure 2 This is a diagram of the shock wave structure taken in the experiment. It can be seen that the shock wave shape and angle in the experimental results are consistent with the simulation results. The present invention can generate gas shock waves of the laser wakefield accelerator, and has the advantages of simple operation, strong stability, and high flexibility.

Claims

1. A gas shock wave generating device for a laser wakefield electron accelerator, characterized in that: include: A trapezoidal obstacle (4) with a circular hole (11), wherein the circular hole (11) is used to allow the ultra-strong ultra-short laser (1) to pass through and interact with the gas shock wave generated by the obstacle; A gas flow stabilizing tube (3) is located above the trapezoidal obstacle (4), and the top of the gas flow stabilizing tube (3) is connected to the high-speed electromagnetic valve (2); A gas storage tank (6) is connected to the gas flow stabilizing tube (3) via the high-speed electromagnetic valve (2); The high-speed solenoid valve (2) is controlled by the solenoid valve controller (8). When the solenoid valve controller (8) receives the signal of the ultra-strong ultra-short laser (1), the high-speed solenoid valve (2) is synchronously controlled to open, so that the gas is ejected from the gas storage tank (6) through the solenoid valve inlet (2-1) and the solenoid valve outlet (2-2) through the gas steady flow tube (3) to the trapezoidal obstacle (4) to generate a shock wave, and the ultra-strong ultra-short laser (1) passes through the circular hole (11) of the trapezoidal obstacle (4) to interact with the gas; Also includes: A vacuum six-dimensional electrically controlled translation stage (5) for placing a trapezoidal obstacle (4); and a solenoid valve bracket (7), one end of which is connected to the high-speed solenoid valve (2) and the other end of which is fixed to the vacuum six-dimensional electric-controlled translation stage (5); The vacuum six-dimensional electric-controlled translation stage (5) has six adjustment dimensions, including overall translation up and down, left and right, and controlling the distance between the high-speed electromagnetic valve (2) and the obstacle (4) to expand and contract, and is used to adjust the overall position so that the laser just passes through the circular hole (11), and to adjust the shock wave position to change the interaction process between the laser and the gas; The cross section of the trapezoidal obstacle (4) is trapezoidal, and the diameter of the circular hole (11) thereon is 1 mm.

2. The gas shock wave generating device of the laser wakefield electron accelerator according to claim 1, characterized in that: The upper end side surface of the gas flow stabilizing tube (3) is provided with a screw hole, and is fixed to the outlet (2-2) of the high-speed electromagnetic valve (2) via screws (9, 10).

3. The gas shock wave generating device of the laser wakefield electron accelerator according to claim 2, characterized in that: The outlet (2-2) of the high-speed solenoid valve (2) is connected to a long straight gas flow stabilizing tube (3), the inner diameter of which is consistent with the inner diameter of the outlet (2-2) of the solenoid valve, and is used to improve the stability of the ejected gas.

4. The gas shock wave generating device of the laser wakefield electron accelerator according to claim 2, characterized in that: The high-speed solenoid valve (2) and the solenoid valve controller (8) are connected via a wire.

5. The gas shock wave generating device of the laser wakefield electron accelerator according to claim 1, characterized in that: The obstacle (4) has an external thread below which is connected and fixed to the screw hole at the upper end of the vacuum six-dimensional electric-controlled translation stage (5).

6. The gas shock wave generating device of the laser wakefield electron accelerator according to claim 1, characterized in that The gas storage tank (6) is external, and the type and pressure of the gas inside can be changed, or it can be a mixture of multiple different types of gases.

7. The gas shock wave generating device of the laser wakefield electron accelerator according to claim 1, characterized in that: The vacuum six-dimensional electric translation stage (5) is electrically adjusted using a computer or an external controller with an adjustment accuracy of 1 micron, and is adjusted and used in a vacuum environment. Its function is to adjust the overall position of the device according to the position and direction of the laser, and to change the structure of the generated gas shock wave.

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