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Discussion on plasma instability of plasma cleaning machine manufacturers

Discussion on plasma instability of plasma cleaning machine manufacturers

Plasma instability can be roughly divided into macroscopic instability and microscopic instability. Where the instability region develops on the micro scale, such as the cyclotron radius and Debye length of the particle, is collectively referred to as the macro instability. An instability that develops only on a microscopic scale is called a microscopic instability. Macroscopic instability can cause a wide range of plasma disturbances, which can seriously damage the equilibrium. The main reason is that the excess energy bound to the magnetic field is stored in the plasma. In addition, the diamagnetism and other characteristics of the plasma also lead to macroscopic instability. This is a very important problem for confined plasmas in controlled thermonuclear fusion devices. There are many types of macro instability. In addition to the distortion instability, the exchange instability is more important, that is, the position of the plasma and the constrained magnetic lift exchange; Ripping modes, where the plasma is torn apart by a magnetic field into tiny beams, and so on. Magnetic fluid dynamics is a commonly used method to study macroscopic instability. In this case, the energy principle is a very effective method, which is to judge whether the equilibrium is stable or not according to the change of the system potential energy caused by the small displacement when the system deviates from the equilibrium. This method is especially suitable for magnetic fields with complex geometry. In addition to the energy principle, the normal mode method is a commonly used analytical method. The method assumes that the perturbation quantity is dq(r,t)=dq(r)-e-iwt. W is usually found as a complex number: W = WR + Iwi. If Wi BBB 0 0, the amplitude of disturbance increases with t, that is, it is unstable; on the contrary, Wi <0, the system is stable. There are many reasons for micro-instabilities. Spatial inhomogeneity, such as density, temperature, magnetic field gradient, etc., which can cause drift and potentially cause instability. Another reason is the inhomogeneity of velocity space, such as anisotropy of velocity, temperature, pressure, etc. In addition, wave to wave interaction and so on can also lead to micro instability. In summary, plasma deviating from thermal equilibrium has excess free energy that must be released to bring it toward equilibrium. The free energy released may cause microscopic instability. Plasmas with micro instability are characterized by increasing fluctuation. This situation often leads to turbulence and anomalous transport. There are many types of micro-instabilities. The main reasons are: secondary instability, which is caused by two beams of particles flowing relative to each other; Drift instability is caused by drift motion caused by various gradients. Loss cone instability caused by anisotropy of velocity distribution, and parametric instability caused by wave-wave interaction, etc. The theory of micro-instability is based on dynamical theory, that is, it starts from the study of Vlasov equation. For the study of instability, linear theory is generally adopted, which can only judge whether the system is stable or not, and sometimes can give the growth rate of instability at the initial moment of the system. The nonlinear theory is needed to study the evolution problem of the perturbation tending to saturation when the amplitude of the perturbation increases under appropriate conditions.

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Discussion on Plasma Relaxation and Transport in Plasma Surface Treatment Factory

Discussion on Plasma Relaxation and Transport in Plasma Surface Treatment Factory

The transition process of non-thermal equilibrium plasma to equilibrium state can be divided into relaxation process and transport process. The former describes a transition from a non-thermal equilibrium velocity distribution to a thermal equilibrium Maxwell distribution, and the latter describes a stable non-thermal equilibrium state, that is, matter, momentum and energy flowing in space, etc. The relaxation process is usually described in terms of different relaxation times, and the basic principle is the collision between charged particles. The interaction between charged particles is the long-duration Coulomb force, a particle can interact with multiple particles in the long range of Debai simultaneously, and they can produce near collisions (two particles collide close together) and far collisions (one particle collides with many particles at a long distance). The collision of charged particles in plasma has a characteristic that the effect of far collision is much greater than that of near collision. The time of conflict and the mean free path L are mainly dependent on the distant conflict. For high temperature plasma, there are three important relaxation times: longitudinal deceleration time, transverse deflection time, and energy homogenization time T ^. The relaxation time of electrons is different from that of ions. In a plasma that is not thermal equilibrium at the beginning, electrons will first reach thermal equilibrium after collision, and then they will reach thermal equilibrium between electrons and ions. Electrical conductivity, permeability, viscosity and thermal conductivity are important parameters in plasma transport. One of the features is bipolar diffusion. For example, electron diffusion, electrostatic energy between electrons and ions makes ions diffuse together, resulting in slower electron diffusion and faster ion diffusion, both of which diffuse at the same rate, namely the so-called bipolar diffusion. In addition, the plasma is in a magnetic field, and the transport along the magnetic field is basically unaffected by the magnetic field, while the transport across the magnetic field is blocked by the magnetic field. Due to the drift caused by the magnetic field gradient, the orbit of the confined particles will change in the high-temperature rarefied plasma in the annular magnetic field, thus increasing the free migration path and greatly improving the transport coefficient. Based on the analysis of this magnetic field configuration, a transport theory, called the Neoclassical theory, is derived, which is still a collision theory. This theory is of great significance for the study of controlled thermonuclear fusion, and it can explain to some extent the large ionic thermal conductivity observed in the ring device. In experiments by Tokamak et al. it was found that some transfer coefficients, such as electron thermal conductivity, were much larger than the results of the neoclassical theory. For some experiments and inertial confinement fusion, we find that the transfer coefficients are much smaller than those obtained by classical theory. Transport phenomena which cannot be explained by any collision theory are called anomalous transport. At present, it is generally believed that anomalous transport is caused by nonlinear process turbulence. The problem of anomalous transport is related to whether the particles and energy of plasma can be effectively controlled, which has become an important subject in current fusion theory research. The above is the CRF plasma surface treatment manufacturers to discuss the plasma relaxation and transport problems, I hope to help you.

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Research Status of Plasma Radiation of Vacuum Plasma Spraying Factory

Research Status of Plasma Radiation of Vacuum Plasma Spraying Factory

The significance of studying plasma radiation lies in: on the one hand, it is an important way of energy dissipation of plasma; on the other hand, the study of plasma radiation is the necessary basis for in-depth understanding of plasma motion law by means of spectrum analysis and other methods. This is particularly important in astrophysics and space physics because the understanding of distant plasmas has been gained almost entirely through the study of radiation. The radiation of plasma includes: bremsstrahlung, cyclotron radiation, blackbody radiation, Cherenkov radiation, and linear radiation in the transition of atoms, molecules or ions. Bremsstrahlung is the collision between free electron and ion, i.e. the continuous radiation produced by electrons when the ion velocity changes in the Coulomb field. Electron-electron collisions do not change the total momentum of the electrons and therefore do not generate bremsstrahlung. Bremsstrahlung in plasma is mainly caused by distant collisions, and its wavelength generally ranges from ultraviolet to X-ray. Radiation loss is a very important problem for high temperature plasmas. Echo radiation, also known as cyclotron radiation, is the radiation produced by charged particles, mainly electrons, as they move in circles around magnetic field lines. The radiation of non-relativistic electrons is called cyclotron radiation, which is a monochromatic radiation that appears in the form of spectral lines at the electron cyclotron frequency. When the electron energy is high, in addition to the fundamental frequency, it also emits radiation in a harmonic frequency. This type of radiation is nearly isotropic and weak in energy. In the plasma, due to collision and other reasons, the spectral line becomes wider, and the frequency of the spectral line moves to the high frequency direction with the increase of the plasma density. The cyclotron radiation of relative electrons is called synchrotron radiation, which has high power, weak directivity, concentrated in a small area, and is a kind of continuous spectrum. The above is the CRF vacuum plasma spraying manufacturer to explain the plasma radiation research status, I hope to help you.

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Plasma generator manufacturer DC discharge to produce plasma theory

Plasma generator manufacturer DC discharge to produce plasma theory

There are two kinds of plasma gas discharge, one is DC and the other is AC. DC discharge usually refers to low-frequency discharge. Under different pressure and current range, due to the number of electrons in gas, collision frequency, particle diffusion and heat transfer velocity are different, there will be dark current area, glow discharge area and arc discharge area. The magnitude of the current depends on the power supply load characteristic curve corresponding to the falling line of resistance R1, R2 and the discharge characteristic curve intersection (operating points A, B, C). 1. Dark current area: The electromagnetic field accelerates the electrons, so that they gain enough energy, through the collision with neutral molecules, the number of new electrons rapidly increased, when the current reaches 10-7~10-5 A, there will be a very thin layer of light near the anode. 2. Glow discharge area: When the current is increased again (10-5~10-1 ampere), the cathode will be bombarded by ions at low pressure and accelerate toward the anode direction, thus giving off electrons. Near the cathode, there is a cathode drop region with a large potential difference. In the middle part between the electrodes, there is a positive column region with a small potential gradient, and the medium is non-equilibrium plasma. When there is no gas convection, electrons and ions in the positive column diffuse towards the wall at the same speed, and combine on the wall, releasing energy. In classical theory, the distribution of electron density on the cross section is in the form of Bessel function. There is an anode potential drop region several millimeters thick near the anode, and its potential difference is basically equal to the gas ionization potential difference. 3. Arc discharge area: When the current exceeds 10-1 A and the pressure is also high, the Joule heat generated in the positive column area is greater than the heat dissipation of the particle diffusion zone to the wall, so that the temperature in the center of the positive column area increases, the gas conductivity increases, so that the current concentrates in the center of the positive column area, forming unstable contraction. The conducting positive column will shrink into an arc with higher temperature and higher current density, that is, arc discharge. The current density is 104~106 A/cm, forming "cathode spot" on the cathode, according to the mechanism of hot electron emission (hot cathode) or field emission (cold cathode), electrons are emitted. There are also "anode spots" on the cathode. Because the electrons carry their kinetic energy into the anode, they release energy equivalent to the work that was lost when they enter the anode. Combined with the heat in the falling region of the anode, the anode heats up much more than the cathode. The above is the CRF plasma generator manufacturers to DC discharge to produce plasma theory discussion, I hope to help you.

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Applications of plasma technology in aerospace field

Applications of plasma technology in aerospace field

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Analysis of factors affecting cleaning efficiency of atmospheric pressure plasma cleaning machine process parameters

Analysis of factors affecting cleaning efficiency of atmospheric pressure plasma cleaning machine process parameters

Low pressure plasma cleaning machine is a typical plasma cleaning equipment. Because the production of plasma needs to be carried out under the condition of low pressure, vacuum equipment and closed system are needed, the cost of equipment is high, the operating space and the size of items to be cleaned are easily limited, which is not conducive to large-scale industrial production. So in recent years, the development of atmospheric plasma and its cleaning technology has attracted much attention. Atmospheric pressure jet plasma spray gun is a capacitance-coupled RF discharge device. Its plasma characteristics are similar to glow discharge. When cleaning the material surface, the working gas can be selected according to the characteristics of the pollutants to be cleaned. In addition, there is a atmospheric air dielectric barrier discharge plasma cleaning device, which can be used to clean the surface of continuous fibers, fabrics and other large fabrics under atmospheric pressure. Dielectric barrier discharge (DBD) can produce macroscopic uniform and stable plasma with high discharge intensity and high processing efficiency. During the cleaning process of atmospheric pressure plasma cleaning machine, the main factors affecting the cleaning efficiency of equipment parameters are as follows: (1) Discharge pressure: in the case of low-voltage plasma, discharge pressure increases, plasma density increases, and electron temperature decreases; The cleaning effect of plasma depends on the density of plasma and the temperature of electrons. The higher the density of plasma, the faster the cleaning speed will be. The higher the temperature of electrons, the better the cleaning effect will be. The discharge pressure selection is the key in the process of low-voltage plasma cleaning. (2) Gas types: there are a variety of pollutants on the substrate and surface of the items to be treated, while the plasma cleaning speed and cleaning effect generated by different gas discharges are widely different. Therefore, working gas plasma should be selected specifically. For example, oxygen plasma can be used to remove oil stains on the surface of objects, and mixed gases such as hydrogen and argon can be used to remove the oxide layer. (3) Discharge power: the greater the discharge power, the greater the density of plasma, the greater the energy of active particles, and the better the cleaning effect. For example, the discharge power has a large effect on the density of oxygen plasma. (4) Contact time: the contact time of the material to be cleaned in the plasma has an important influence on the cleaning effect of the plasma and the working efficiency of the plasma. Long contact time, the cleaning effect is better, but the work efficiency is reduced. Also, too long cleaning time can cause damage to the material surface. (5) transmission speed: for atmospheric plasma cleaning process, continuous transmission will be involved when dealing with large objects. The results show that the slower the relative moving speed of the cleaned object and electrode is, the better the treatment effect is. However, too slow a speed on the one hand affects the work efficiency, on the other hand, it will cause damage to the material surface, and the treatment time is too long. (6) Others: parameters such as gas distribution, gas flow rate and electrode setting in the cleaning process of atmospheric pressure plasma cleaning machine will also have an impact on the cleaning effect. Therefore, specific process parameters should be set according to the actual situation and cleaning requirements.

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