CN117691437A - Electron beam-plasma system terahertz radiation source based on adjustable grating - Google Patents

Abstract

The invention discloses a terahertz radiation source of an electron beam-plasma system based on an adjustable grating, wherein a medium tube is arranged in a vacuum cavity, a plasma channel is formed in the medium tube, an electron beam passes through the plasma channel to excite a plasma wave, a Buluoch mode is formed on the surface of the adjustable grating on the outer wall of the medium tube, harmonic waves with wave numbers smaller than that of electromagnetic waves with the same frequency can be converted into a radiation field, and the radiation is emitted to the outside from the surface of the adjustable grating, so that terahertz radiation output is formed. The adjustable grating is used as a coupler to realize field matching of the plasma wave and terahertz electromagnetic radiation, so that the energy of the fundamental frequency plasma wave is effectively extracted; and the adjustable grating is used as a controller, and the working parameters of the terahertz radiation source are controlled by changing the period and voltage of the adjustable grating.

Description

Electron beam-plasma system terahertz radiation source based on adjustable grating

Technical field

The invention belongs to the technical field of terahertz radiation sources, and more specifically, relates to an electron beam-plasma system terahertz radiation source based on an adjustable grating.

Background technique

The electron beam-plasma system is a new type of high-power electromagnetic radiation source with huge application potential in the terahertz field. Its working principle is divided into two steps: 1. Use high-energy electron beams to pass through high-density plasma and drive plasma waves (i.e., electron electrostatic waves) with frequencies located at the plasma frequency (fundamental frequency) and its multiples through dual-flow instability; 2. The system transfers the energy of plasma waves to electromagnetic waves by stimulating various electromagnetic instability mechanisms to achieve electromagnetic radiation. In the second step of the above principle, there is an important problem that restricts the efficiency of this type of radiation source, that is, the energy conversion efficiency of the plasma wave fundamental frequency is low.

Currently, there are three potential mechanisms for converting fundamental frequency plasma waves into terahertz radiation: 1. Cherenkov radiation in magnetized plasma; 2. Scattering of plasma waves by ion thermal motion; 3. Plasma Coherent scattering of waves on ion waves (or ion density modulation). The above three methods all have the disadvantage of low radiation conversion efficiency, and usually the energy conversion efficiency is less than one thousandth. Since when the electron beam interacts with the plasma, more than 90% of the energy handed over by the electrons is stored in the fundamental frequency plasma wave. However, it is difficult for traditional methods to effectively extract the energy of the fundamental frequency plasma wave, which limits this Energy conversion efficiency of radiation-like sources.

At the same time, the radiation frequency, direction, and power of traditional electron beam-plasma systems are difficult to control. This is because these parameters depend on the electron density distribution of the plasma, and plasma diffuses in free space, so it needs to be controlled to achieve a suitable distribution state.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology, provide an electron beam-plasma system terahertz radiation source based on an adjustable grating, and use the adjustable grating as a coupler to achieve field matching between plasma waves and terahertz electromagnetic radiation. , thereby effectively extracting the energy of the fundamental frequency plasma wave; and using the tunable grating as a controller to control the operating parameters of the terahertz radiation source by changing the period and voltage of the tunable grating.

In order to achieve the above-mentioned object of the invention, the terahertz radiation source of the electron beam-plasma system based on the adjustable grating of the present invention includes a vacuum chamber, a dielectric tube, an air inlet, an exhaust hole, an electrode, a metal foil at the front end of the dielectric tube, and a rear end of the dielectric tube. Metal foil, grating, electron beam emission source, electron beam collector and output window, where:

The air inlet and exhaust holes are provided on the side wall of the vacuum chamber;

The medium tube is located inside the vacuum chamber. A branch outlet is provided on the side of the front opening and the rear opening of the medium tube, respectively connected to the air inlet and the exhaust hole, for filling the working gas into the medium tube; the front end of the medium tube The opening is covered with metal foil at the front end of the medium tube, and the rear end opening is covered with metal foil at the rear end of the medium tube;

The adjustable grating is located inside the vacuum chamber and is installed on the outer wall of the dielectric tube. Its grating surface is parallel to the incident direction of the electron beam;

The electron beam emission source and electron beam collector are located inside the vacuum chamber and are respectively arranged at the front end opening and the rear end opening of the dielectric tube. The electron beam emission source emits the electron beam from the front end opening of the dielectric tube, and the electron beam passes through the medium. The tube emerges from the rear end opening and is received by the electron beam collector;

The output window is set at the position corresponding to the adjustable grating on the side wall of the vacuum chamber, and is used to output terahertz electromagnetic waves;

The workflow to realize terahertz wave radiation is as follows:

The working gas is fed into the dielectric tube from the air inlet, and an electric pulse with a preset repetition frequency and voltage is applied to the electrode at the same time to ionize the working gas into plasma; the plasma moves with the air flow and fills the dielectric tube, forming plasma inside the dielectric tube. body channel, and the remaining gas is discharged through the exhaust hole;

The electron beam emission source in the vacuum chamber emits an electron beam. The electron beam passes through the metal foil at the front end of the dielectric tube and enters the plasma channel. It interacts with the plasma to excite plasma waves in the terahertz band; subsequently, the electron beam passes through the dielectric tube. The terminal metal foil leaves the plasma channel and is eventually absorbed by the electron beam collector;

The plasma wave forms a Bloch mode on the surface of the tunable grating, in which harmonics with a wave number smaller than that of the electromagnetic wave of the same frequency can be converted into a radiation field and radiated from the surface of the tunable grating to the outside world. The formed terahertz radiation is output from the output window. .

The invention is based on an electron beam-plasma system terahertz radiation source with an adjustable grating. A dielectric tube is arranged inside the vacuum chamber, and a plasma channel is formed inside the dielectric tube. The electron beam passes through the plasma channel to excite plasma waves. The tunable grating surface on the outer wall forms a Bloch mode, in which harmonics with wave numbers smaller than those of electromagnetic waves of the same frequency can be converted into radiation fields and radiated from the tunable grating surface to the outside world, thereby forming terahertz radiation output.

The invention has the following beneficial effects:

1) The present invention establishes field matching between plasma waves and electromagnetic radiation through an adjustable grating, which can effectively realize the radiation of plasma fundamental frequency wave energy and fundamentally solve the problem of low radiation efficiency of the electron beam-plasma system.

2) The present invention proposes a more convenient control method, which can solve the problem of difficulty in controlling the radiation parameters of the traditional electron beam-plasma system. That is, by changing the voltage of the adjustable grating, the terahertz radiation frequency, power and Adjustment of efficiency; by changing the period of the adjustable grating, the radiation direction, power and efficiency can be adjusted.

Description of the drawings

Figure 1 is a structural diagram of a specific embodiment of the terahertz radiation source of the electron beam-plasma system based on the adjustable grating of the present invention;

Figure 2 is the electric field distribution diagram inside the simulation area at 154.2ps in this embodiment;

Figure 3 is a terahertz radiation spectrum diagram of grating-coupled plasma wave emission in this embodiment;

Figure 4 is a schematic diagram of the power and energy conversion efficiency of the radiation field in this embodiment.

Detailed ways

Specific embodiments of the present invention will be described below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the present invention. It is important to note that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

Example

Figure 1 is a structural diagram of a specific embodiment of the terahertz radiation source of the electron beam-plasma system based on the adjustable grating of the present invention. As shown in Figure 1, the terahertz radiation source of the electron beam-plasma system based on the adjustable grating of the present invention includes a vacuum chamber 1, a dielectric tube 2, an air inlet 3, an exhaust hole 4, an electrode 5, and a metal foil at the front end of the dielectric tube. 6. Metal foil 7 at the rear end of the dielectric tube, grating 8, electron beam emission source 9, electron beam collector 10 and output window 11, among which:

The air inlet 3 and the exhaust hole 4 are provided on the side wall of the vacuum chamber 1;

The medium pipe 2 is located inside the vacuum chamber 1. The front and rear openings of the medium pipe 2 are respectively provided with a branch outlet 21 and 22 on the side, which are respectively connected to the air inlet 3 and the exhaust hole 4 for supplying air to the medium pipe 2. Fill with working gas. The front opening of the medium tube 2 is covered with the metal foil 6 at the front end of the medium tube, and the rear end opening is covered with the metal foil 7 at the rear end of the medium tube. The metal foil 6 at the front end of the dielectric tube and the metal foil 7 at the rear end of the dielectric tube are used to seal the dielectric tube 2, which can isolate the electron beam source and the working gas to prevent leakage, while only allowing high-energy electron beams to pass through.

The adjustable grating 8 is located inside the vacuum chamber 1 and is arranged on the outer wall of the dielectric tube 2. Its grating surface is parallel to the incident direction of the electron beam. After research, it is found that the optimal period length D∈[0.1L, 10L] of the tunable grating 8, L represents the wavelength of the plasma wave. The distribution position and size of the adjustable grating 8 in the medium tube 2 can be set according to actual needs.

The electron beam emission source 9 and the electron beam collector 10 are located inside the vacuum chamber 1 and are respectively arranged at the front end opening and the rear end opening of the dielectric tube 2. The electron beam emission source 9 injects electron beams from the front end opening of the dielectric tube 2. , the electron beam passes through the dielectric tube 2 and is emitted from the rear end opening, and is received by the electron beam collector 10.

The output window 11 is provided at a position corresponding to the adjustable grating 8 on the side wall of the vacuum chamber 1, and is used to output terahertz electromagnetic waves.

The work flow of this invention to realize terahertz wave radiation is as follows:

The working gas is sent into the dielectric tube 2 from the air inlet 3, and at the same time, an electric pulse with a preset repetition frequency and voltage is applied to the electrode 5 to ionize the working gas into plasma. Experimental research has found that for terahertz wave radiation, the repetition frequency of the electric pulse is in the range of 1 to 100kHz, and the voltage is in the range of 1 to 50kV, which has better effects. The plasma moves with the air flow and fills the medium tube 2 , forming a plasma channel inside the medium tube 2 , and the remaining gas is discharged through the exhaust hole 4 . The density of the plasma channel is on the order of 10 ²⁰ to 10 ²⁴ m ^-3 .

The electron beam emission source 9 in the vacuum chamber 1 emits an electron beam, which passes through the metal foil 6 at the front end of the dielectric tube, enters the plasma channel, and interacts with the plasma to excite plasma waves in the terahertz band. Subsequently, the electron beam passes through the metal foil 7 at the rear end of the dielectric tube and leaves the plasma channel, and is finally absorbed by the electron beam collector 10 .

The plasma wave forms a Bloch mode on the surface of the adjustable grating 8, in which the harmonics with a wave number smaller than the wave number of the electromagnetic wave of the same frequency can be converted into a radiation field, which is radiated from the surface of the adjustable grating 8 to the outside world, and the resulting terahertz radiation is output from Window 11 output.

It has been found through research that the direction and output power of terahertz radiation can be adjusted by adjusting the period of the adjustable grating 8 . By applying voltage to the adjustable grating 8, the plasma electron density distribution under the grating can be changed, thereby adjusting the terahertz radiation frequency, and realizing a controllable terahertz radiation source based on the electron beam-plasma system.

In order to illustrate the technical effects of the present invention, specific examples are used to conduct experimental simulations of the present invention. In this embodiment, PIC particle simulation is used to simulate and demonstrate the terahertz radiation source of the electron beam-plasma system loaded with an adjustable grating. In the simulation, it is considered to adjust the voltage of the adjustable grating 8 to maintain the electron plasma density under the adjustable grating 8 at 1×10 ²² m ^-3 . The inner diameter of the plasma channel is 0.3mm, the length is 1.2cm, and the tube wall thickness is 0.05 mm. After calculation, it can be found that the fundamental frequency of the plasma wave is 0.9THz. The electron beam diameter is 0.1mm, the electron beam density is 1.0×10 ¹⁸ m ^-3 , and the acceleration voltage is 511kV. The adjustable grating 8 is located on the upper tube wall of the medium tube 2, and its period is equal to the plasma wavelength.

Figure 2 is the electric field distribution diagram inside the simulation area at 154.2ps in this embodiment. Figure 2 shows an image of an electron beam passing through a plasma channel, driving the plasma wave, and emitting terahertz radiation under the action of a tunable grating. The small squares arranged periodically in the horizontal direction in Figure 2 are tunable gratings; below the tunable grating 8 is the plasma wave propagating in the horizontal direction, and above the tunable grating 8 is the terahertz radiation propagating in the vertical direction. . Since there is no adjustable grating underneath the dielectric tube 2, it can be found that the electromagnetic radiation intensity without the grating is far less than that with the grating.

Figure 3 is a terahertz radiation spectrum diagram of grating-coupled plasma wave emission in this embodiment. The monitoring position shown in Figure 3 is located at the star point in Figure 2. It can be seen from Figure 3 that after adding a grating, the intensity of the plasma wave with a fundamental frequency of 0.9THz is much higher than the higher harmonics.

Figure 4 is a schematic diagram of the power and energy conversion efficiency of the radiation field in this embodiment. As can be seen from Figure 4, the obtained fundamental frequency wave radiation power can reach the kilowatt level, and the energy conversion efficiency can reach the order of one percent, exceeding the level of traditional miniaturization solutions. Figure 4 also reflects the adjustment effect of adjustable grating voltage on radiation power and efficiency. The abscissa in the figure is the amplitude of changes in plasma electron density caused by different grating voltages (normalized to the initial density). It can be found that different grating voltages can produce changes in electron density. Under different changes in electron density, the power and energy conversion efficiency of terahertz radiation change significantly. This result shows that it is feasible to use gratings to control the radiation parameters of the electron beam-plasma system.

Although the illustrative specific embodiments of the present invention are described above to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, As long as the various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

Claims (4)

1. An electron beam-plasma system terahertz radiation source based on an adjustable grating, which is characterized by including a vacuum chamber, a dielectric tube, an air inlet, an exhaust hole, an electrode, a metal foil at the front end of the dielectric tube, and a rear end of the dielectric tube. Metal foil, grating, electron beam emission source, electron beam collector and output window, where: The air inlet and exhaust holes are arranged on the side wall of the vacuum chamber; The medium tube is located inside the vacuum chamber. A branch outlet is provided on the side of the front opening and the rear opening of the medium tube, respectively connected to the air inlet and the exhaust hole, for filling the working gas into the medium tube; the front end of the medium tube The opening is covered with metal foil at the front end of the medium tube, and the rear end opening is covered with metal foil at the rear end of the medium tube; The adjustable grating is located inside the vacuum chamber and is installed on the outer wall of the dielectric tube. Its grating surface is parallel to the incident direction of the electron beam; The electron beam emission source and electron beam collector are located inside the vacuum chamber and are respectively arranged at the front end opening and the rear end opening of the dielectric tube. The electron beam emission source emits the electron beam from the front end opening of the dielectric tube, and the electron beam passes through the medium. The tube emerges from the rear end opening and is received by the electron beam collector; The output window is set at the position corresponding to the adjustable grating on the side wall of the vacuum chamber, and is used to output terahertz electromagnetic waves; The workflow to realize terahertz wave radiation is as follows: The working gas is fed into the dielectric tube from the air inlet, and an electric pulse with a preset repetition frequency and voltage is applied to the electrode at the same time to ionize the working gas into plasma; the plasma moves with the air flow and fills the dielectric tube, forming plasma inside the dielectric tube. body channel, and the remaining gas is discharged through the exhaust hole; The electron beam emission source in the vacuum chamber emits an electron beam. The electron beam passes through the metal foil at the front end of the dielectric tube and enters the plasma channel. It interacts with the plasma to excite plasma waves in the terahertz band; subsequently, the electron beam passes through the dielectric tube. The terminal metal foil leaves the plasma channel and is eventually absorbed by the electron beam collector; The plasma wave forms a Bloch mode on the surface of the tunable grating, in which harmonics with a wave number smaller than that of the electromagnetic wave of the same frequency can be converted into a radiation field and radiated from the surface of the tunable grating to the outside world. The formed terahertz radiation is output from the output window. . 2. The electron beam-plasma system terahertz radiation source according to claim 1, characterized in that the period length D∈[0.1L, 10L] of the adjustable grating, L represents the wavelength of the plasma wave. 3. The electron beam-plasma system terahertz radiation source according to claim 1, characterized in that the repetition frequency of the electrical pulse is in the range of 1 to 100 kHz, and the voltage is in the range of 1 to 50 kV. 4. The electron beam-plasma system terahertz radiation source according to claim 1, characterized in that the density of the plasma channel is on the order of 10 ²⁰ to 10 ²⁴ m ^-3 .