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Discussion on Plasma Relaxation and Transport in Plasma Surface Treatment Factory

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20 Mar,2021

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.

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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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