阅读说明：本技术 10GeV电子加速的多级气体靶系统 (10GeV electron accelerated multi-stage gas target system ) 是由 徐建彩 沈百飞 徐同军 李顺 徐张力 于 2020-07-03 设计创作，主要内容包括：一种适用于10GeV电子加速的多级气体靶系统。包括多个气体靶单元、级间连接装置和气体靶调节装置等。本发明首次提出利用3级及以上的多级气体靶方案,有效调控气体靶的长度和纵向密度分布曲线,实现电子束的长距离加速而将电子束能量提升至10GeV及以上。本发明对激光驱动尾场加速研究中突破10GeV能量挑战提供了可行的气体靶实现方案,技术上可以通过多级气体盒子或者毛细管来实现。(A multi-stage gas target system suitable for 10GeV electron acceleration. Comprises a plurality of gas target units, an interstage connecting device, a gas target regulating device and the like. The invention firstly proposes a scheme of utilizing a multi-stage gas target with 3 stages or more, effectively regulates and controls the length and the longitudinal density distribution curve of the gas target, realizes the long-distance acceleration of the electron beam and improves the energy of the electron beam to 10GeV or more. The invention provides a feasible gas target implementation scheme for breaking through the 10GeV energy challenge in laser-driven tail field acceleration research, and can be technically implemented by a multi-stage gas box or a capillary tube.)

1. A multi-stage gas target system suitable for 10GeV electron acceleration is characterized by comprising N stages of gas target units (A), N-1 inter-stage connecting devices (B), a gas target adjusting device (C) and N-1 supporting structures (D), wherein the gas target adjusting device (C) comprises a five-dimensional electric target table (C-1) and a translation table controller (C-2), the N gas target units (A) are composed of N-1 gas target units (A-a) with fixed lengths and one gas target unit (A-B) with adjustable lengths, and N is a positive integer larger than or equal to 3. The single gas target unit (A-a) with fixed length comprises a gas target main body structure (A-1), a transparent material observation window (A-2), a gas inlet pipeline (A-3), a gas pressure sensor (A-4), a gas pressure controller (A-5) and a high-pressure gas cylinder (A-6). The gas target main structure (A-1) is connected with the high-pressure gas cylinder (A-6) through the gas inlet pipeline (A-3), the gas pressure controller (A-5) is arranged on the gas inlet pipeline (A-3), and the transparent material observation window (A-2) and the gas pressure sensor (A-4) are arranged on the gas target main structure (A-1). The structure of the length-adjustable gas target unit (A-b) comprises a structure which is the same as that of the length-fixed gas target unit (A-a), and a one-dimensional electric translation table (A-7). The five-dimensional electric target platform (C-1) is sequentially provided with the N-1 supporting structures (D) and the one-dimensional electric translation platform (A-7), the N-1 gas target units (A-a) with fixed lengths are respectively and sequentially arranged on the N-1 supporting structures (D) along the laser propagation direction, the one-dimensional electric translation platform (A-7) is provided with the gas target units (A-B) with adjustable lengths, the N-1 gas target units (A-a) with fixed lengths and the gas target units (A-B) with adjustable lengths are sequentially connected and communicated with each other in a common optical axis through the N-1 interstage connecting devices (B), except the high-pressure gas cylinder (A-6) and a part of gas inlet pipelines (A-3), all devices are located within a vacuum target chamber.

2. The multi-stage gas target system according to claim 1, wherein the fixed length gas target unit (a-a) has a length of 1cm to 20 cm.

3. The multi-stage gas target system of claim 1, wherein the adjustable maximum length of the length-adjustable gas target unit (a-b) is set to L according to experimental requirements, the one-dimensional electric translation stage (a-7) needs to satisfy the adjustment range of 0-Lcm, the adjustment precision is less than 1mm, and the achievable maximum length is 20 cm.

4. The gas target system of claim 1, wherein the interstage connection device (B) is a bidirectional hollow rubber ring with a hollow diameter <1mm, so that the main laser pulse passes through the interstage connection device, and the gas targets at different stages can be effectively connected without gaps, the gas density is kept continuous, and the parameters of the gas targets at different stages are relatively independent.

5. The multistage gas target conditioning device according to claim 1, characterized in that the multistage gas target is placed on a five-dimensional electric target table through a support structure (D) to achieve overall attitude conditioning of the multistage gas target.

Technical Field

The invention relates to the research field of interaction of femtosecond relativistic super-strong laser pulse and plasma, in particular to a gas target system suitable for ultra-high energy electron acceleration.

Background

Rapid development in the field of laser-driven electronic acceleration research relies on rapid advances in femtosecond laser technology. Up to now, several tiles (PW, 10) in the world¹⁵Tile) Stable operation of laser device, 10PThe W laser devices are also built one after the other, and gradually enter into the physical experiment stage. Especially in China, a plurality of 10PW femtosecond laser devices and one 100PW femtosecond laser device are built in a plurality of years. With the increasing output power of laser pulse, the novel development of the compact particle acceleration field can be brought. The electron acceleration based on the ultra-strong femtosecond laser pulse drive can obtain an acceleration field as high as 100GV/m, which is more than three orders of magnitude higher than that of the traditional accelerator, so the acceleration distance is three orders of magnitude smaller, and the establishment of a compact accelerator is possible. The generation of the ultrafast high-quality GeV electron beam has profound influence on future free electron laser, laboratory celestial body physics, high-energy physics and the like, such as high-brightness gamma light sources, strong-field QED physics, future positive and negative electron colliders and the like which need high-stability high-quality 1-10 GeV or even higher-energy electron beams.

Since forty years now, the theory proposed by Tajima et al for laser-driven electron acceleration, the most widespread and stable acceleration mechanism has been studied as the cavitation mechanism for laser tail field acceleration. In 2006, Leemans et al used a capillary gas target 3cm long to break through the electron beam energy of 1 GeV; then in 2014, the same research group improves the energy of the electron beam to 4.2 GeV; the energy of the electron beam was not further increased to 7.8GeV until 2019. It can be seen that the difficulty of continuing to increase increases nonlinearly after the electron beam energy reaches GeV. The reason for this is that long-distance transmission of a stable cavitation structure cannot be effectively achieved. Previous theories indicate that the factors limiting the increase of the energy of the laser tail field accelerated electron beam mainly come from three aspects, namely the dephasing length of the electron beam, the energy loss length of the laser and the defocusing effect. By reducing the gas density, the dephasing length of the electron beam can be effectively increased, but after the gas density is reduced, the corresponding acceleration field gradient also decreases, requiring a longer acceleration distance. Theory suggests that the length of the gas target facing the 10GeV electron acceleration is at least 25 cm.

At present, a low-density gas target (<1×10¹⁸cm^-3) Is increased to>There are two solutions for 10 cm: capillary tubes and gas boxes.

The capillary tube generally needs to be added with high voltage at two ends, a plasma channel is generated through discharge, a low-density gas target with relatively uniform longitudinal density distribution can be provided, and the length of a single stage is 20cm at most at present.

The gas-filled box is another scheme for realizing high-energy electron acceleration based on a low-density gas target; the transverse size of the gas box is generally larger than 1cm, the size of small holes at two ends of the gas box is generally 1-2 mm, the gas box is used for transmitting laser pulses, and the length of the single-stage gas box can reach 15 cm; as the length of single stage gas targets continues to increase, longitudinal uniformity control of the gas targets presents a great technical challenge. Meanwhile, the theory of laser tail field electron acceleration shows that the regular change of longitudinal gas density is adjustable, which is more beneficial to optimizing the electron acceleration process and improving the output energy of electron beams. In the current experiment, the injection process and the acceleration process of the electron beam can be separated by utilizing two-stage acceleration, the feasibility of cascade acceleration is verified in principle, and the energy of the electron beam is close to GeV. If the energy bottleneck of the electron beam of 10GeV is solved, it is necessary to optimize the acceleration process of the electron beam by regulating and controlling the longitudinal density of the gas. The feasible regulation scheme is a multi-stage cascade acceleration scheme of the gas target, and the acceleration stage is more than or equal to 3 stages except the injection stage. Therefore, if electron acceleration studies achieve a 10GeV energy breakthrough, a multi-stage gas target system is essential.

Disclosure of Invention

The invention mainly aims to provide a multistage gas target system for multistage cascade acceleration of electrons, which breaks through the energy bottleneck of 10GeV in the electron acceleration of a tail field driven by ultra-strong laser. The system has the characteristics of practicability, flexibility and the like, and can realize the length adjustment of the gas target and the controllability of the multi-section rule of the longitudinal density curve.

The technical solution of the invention is as follows:

a multi-stage gas target system suitable for 10GeV electron acceleration is characterized by comprising more than N stages of gas target units, N-1 interstage connecting devices, a gas target adjusting device and N-1 supporting structures, wherein the gas target adjusting device comprises a five-dimensional electric target table and a translation table controller, the N gas target units are composed of N-1 gas target units with fixed lengths and a gas target unit with adjustable length, and N is a positive integer larger than or equal to 3. The single gas target unit with fixed length comprises a gas target main body structure, a transparent material observation window, a gas inlet pipeline, a gas pressure sensor, a gas pressure controller and a high-pressure gas cylinder. The gas inlet pipeline connects the gas target main body structure with the high-pressure gas cylinder, the gas pressure controller is arranged on the gas inlet pipeline, the transparent material observation window and the gas pressure sensor are arranged on the gas target main body structure, the length-adjustable gas target unit comprises a structure which is the same as that of the length-fixed gas target unit, a one-dimensional electric translation table is further included, N-1 supporting structures and a one-dimensional electric translation table are sequentially arranged on the five-dimensional electric target table, the N-1 length-fixed gas target units are sequentially arranged on the N-1 supporting structures along the laser transmission direction, the length-adjustable gas target unit is arranged on the one-dimensional electric translation table, and the N-1 length-fixed gas target units and the length-adjustable gas target unit are connected through the N-1 interstage connecting device The units are sequentially connected and communicated with each other on a common optical axis, and all devices except the high-pressure gas cylinder and part of the gas inlet pipeline are positioned in the vacuum target chamber.

The length of the gas target unit with the fixed length is 1 cm-20 cm.

The adjustable maximum length of the gas target unit with the adjustable length is set to be L according to experimental requirements, the one-dimensional electric translation table needs to meet the adjustment range of 0-Lcm, the adjustment and control precision is less than 1mm, and the achievable maximum length is 20 cm.

The interstage connecting device is a bidirectional hollow rubber ring, the hollow diameter is less than 1mm, so that main laser pulses pass through the interstage connecting device, meanwhile, the gas targets at all stages can be effectively connected without gaps, the gas density is kept continuous, and the parameters of the gas targets at all stages are relatively independent.

Each stage of the gas target unit can realize independent measurement and control of gas target parameters. After the multi-stage gas target is combined, the multi-stage gas target is placed on a five-dimensional electric target table through a supporting structure, and the overall attitude adjustment of the multi-stage gas target is realized through an electric translation table.

The invention has the following technical effects:

the invention has the characteristics of practicability, flexibility and the like, can realize the length adjustment of the gas target and can control the multi-section rule of the longitudinal density curve.

The invention firstly proposes a scheme of utilizing a multi-stage gas target with 3 stages or more, effectively regulates and controls the length and the longitudinal density distribution curve of the gas target, realizes the long-distance acceleration of the electron beam and improves the energy of the electron beam to 10GeV or more. The invention provides a feasible gas target implementation scheme for breaking through the 10GeV energy challenge in laser-driven tail field acceleration research, and can be technically implemented by a multi-stage gas box or a capillary tube.

Drawings

FIG. 1 is a schematic diagram of a multi-stage gas target system of the present invention.

FIG. 2 is a schematic diagram of an independent control structure of a single gas target unit.

Detailed Description

In order that the embodiments of the invention will be readily understood, specific embodiments thereof will be described below in detail with reference to the accompanying drawings. It should be noted that the present invention should not be limited to the details of the following embodiments, and those skilled in the art should understand the present invention from the spirit embodied in the following embodiments, and each technical term can be understood in the broadest sense based on the spirit of the present invention.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a multi-stage gas target system according to the present invention. The invention is suitable for a multistage gas target system for 10GeV electron acceleration, and comprises A, N-1 interstage connecting devices B of gas target units with more than N stages, a gas target adjusting device C and N-1 supporting structures D, wherein the gas target adjusting device C comprises a five-dimensional electric target table C-1 and a translation table controller C-2, the N gas target units A are composed of N-1 gas target units A-a with fixed length and one gas target unit A-B with adjustable length, and N is a positive integer more than or equal to 3. Referring to fig. 2, the single gas target unit a-a with a fixed length comprises a gas target main structure a-1, a transparent material observation window a-2, a gas inlet pipeline a-3, a gas pressure sensor a-4, a gas pressure controller a-5 and a high pressure gas cylinder a-6, the gas inlet pipeline a-3 connects the gas target main structure a-1 with the high pressure gas cylinder a-6, the gas pressure controller a-5 is arranged on the gas inlet pipeline a-3, the transparent material observation window a-2 and the gas pressure sensor a-4 are arranged on the gas target main structure a-1, the gas target unit a-b with an adjustable length comprises a structure which is the same as the gas target unit a-a with a fixed length, the laser device also comprises a one-dimensional electric translation table A-7, wherein the N-1 supporting structures D and the one-dimensional electric translation table A-7 are sequentially arranged on the five-dimensional electric target table C-1, the N-1 gas target units A-a with fixed lengths are sequentially arranged on the N-1 supporting structures D along the laser transmission direction, the gas target units A-B with adjustable lengths are arranged on the one-dimensional electric translation table A-7, the N-1 gas target units A-a with fixed lengths and the gas target units A-B with adjustable lengths are sequentially connected and communicated with each other through the N-1 interstage connecting devices B on a common optical axis, except the high-pressure gas cylinder A-6 and part of the gas inlet pipeline A-3, all devices are located within a vacuum target chamber (see in detail the dashed box of fig. 2).

The length of the gas target unit A-a with the fixed length is 1 cm-20 cm.

The adjustable maximum length of the gas target unit A-b with the adjustable length is set to be L according to experimental requirements, the one-dimensional electric translation table A-7 needs to meet the adjustment range of 0-Lcm, the adjustment and control precision is less than 1mm, and the achievable maximum length is 20 cm.

The interstage connecting device B is a bidirectional hollow rubber ring, the hollow diameter is less than 1mm, so that main laser pulses can pass through the interstage connecting device, meanwhile, the gas targets at all stages can be effectively connected without gaps, the gas density is kept continuous, and the parameters of the gas targets at all stages are relatively independent.

The multi-stage gas target is placed on a five-dimensional electric target table through a supporting structure D, and overall posture adjustment of the multi-stage gas target is achieved.

A plurality of gas target units are connected in sequence, placed on the same five-dimensional electric target table, combined with a multi-stage gas target system, and main laser pulses enter the multi-stage gas target from the inlet of the gas target unit on the left side and are output from the right side after interacting with the gas target.

FIG. 1 shows the combination of multi-stage gas targets by taking the combination of 3 fixed-length gas target units (5cm) and one adjustable-length gas target unit (adjustment range of 0-10 cm). The 4-stage gas target structure can realize continuous adjustment of the length of the gas target within the range of 15-25cm in the experimental process.

Currently a single stage gas target of 20cm length is technically feasible, but only provides a single longitudinal gas density profile. And the total length can also be realized by 20cm after the 4-stage gas target shown in FIG. 1 is combined. However, in the scheme of combining four gas target units, the gas density distribution of 20cm in length can be divided into four sections for independent control, so that the rising or the falling of a longitudinal gas density curve can be regulated and controlled, a feasible gas target realization scheme is provided for optimizing the acceleration process of electrons in the acceleration of 10GeV electrons, and the problem of sectional control of the longitudinal gas density curve is technically solved.

The schematic structure of fig. 1 is merely an example of a typical gas target combination, and in actual operation, the combination of the gas target units can be flexibly varied. Increasing the length of the entire gas target is achieved, for example, by increasing the length of each gas target unit, e.g., to 10cm, or increasing the number of gas target units, e.g., to 5 gas target units. In addition, the gas target units with different lengths can be freely arranged and combined to realize the length adjustment of the gas target and the sectional adjustment of the longitudinal density of the gas target. In the experimental implementation process, the interstage connection device is difficult to perform, and the interstage connection device, namely the bidirectional hollow rubber ring, can effectively achieve that the connection between all stages of gas targets is free of gaps, and the gas density is kept continuous.

Fig. 2 shows the structure of a single gas target unit. Comprises a main body structure A-1 of a gas target unit, an observation window A-2 made of transparent material, a pressure sensor A-4, a pressure controller A-5, an air inlet pipeline A-3 and a high-pressure gas cylinder A-6. It can be seen that each gas target unit has a separate gas inlet line a-3 connecting the gas target unit body structure a-1 to a high pressure gas cylinder a-6 outside the vacuum target chamber. The air pressure sensor A-4 and the air pressure controller A-5 are matched for use, so that the stable control of the pressure intensity is realized. In view of manufacturing feasibility, the gas target unit with fixed length generally has a minimum size of 1cm and a maximum length of 20cm, otherwise, the manufacturing difficulty of the gas target is greatly increased in terms of the current processing technology.

In the design scheme of the multistage gas target, each gas target unit is independently controlled, namely, an additional set of independent gas inlet pipeline and an air pressure control system are correspondingly added when one gas target unit is added, so that the processing cost and the technical difficulty are increased. At the same time, the control system also needs to ensure time synchronization, i.e. increasing the implementation risk of the whole gas target system. Therefore, the number and the set length of the gas target units are reasonably selected according to the actual requirements on the length of the gas target and the gas density curve in the experiment.

The above-described embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the scope of the present invention, and various modifications and changes can be made to the present invention, but any modifications, equivalents, improvements, etc. made based on the design principle of the present invention should be included in the scope of the present invention.