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Register a new userApplication of classical models to high resolution electric field strength falls in a hydrogen glow-discharge
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Veronica Gonzalez Fernandez
Publication date
2020
fields
Physics
and research's language is
English
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This paper presents the application of two classical models to high-resolution electric field measurements carried out in a hollow cathode discharge operated in pure hydrogen plasma. The electric field determination has been done via the Stark shifting and splitting of the 2S level of hydrogen, followed by optogalvanic detection. Two classical models, Rickards and Wro{n}skis, are applied to these measurements with the objective of obtaining a first estimation on the discharge dynamics. The chosen models provide an idea of the ions movement, their energy and their mean free path at the cathode fall region, as well as the electric field strength behaviour depending on the discharge characteristics.
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The electron sheath formation in a DC magnetised plasma of modified hollow cathode source is studied. The discharge consists of two plane parallel cathodes and a small cubical anode placed off axis at the center. The argon plasma is produced and the properties of the plasma in response to the sheath formation near the anode are studied using electrical and optical diagnostics. In particular, the effect of pressure, magnetic field on discharge parameters such as discharge current, plasma potential, plasma density and electron temperature is studied. The discharge showed an onset of anode glow at a critical applied magnetic field indicating the formation of electron sheath and a double layer. The discharge current initially decreases; however it starts to rise again as the anode spot appears on the anode. The critical magnetic field at which anode glow formation takes place is dependent upon operating pressure and discharge voltage. The transition from ion sheath to electron sheath is investigated in detail by Langmuir probe and spectroscopy diagnostics. The plasma potential near the anode decreases during the transition from ion sheath to electron sheath. The plasma potential locks to the ionization potential of argon gas when anode spot is completely formed. A systematic study showed that during the transition, the electron temperature increases and plasma density decreases in the bulk plasma. The spectroscopy of the discharge showed presence of strong atomic and ionic lines of argon. The intensity of these spectral lines showed a dip during the transition between two sheaths. After the formation of the anode spot, oscillations of the order of 5-20 kHz are observed in the discharge current and floating potential due to the enhanced ionisation and excitation processes in the electron sheath.
Nanoparticles grown in a plasma are used to visualize the process of film deposition in a pulsed radio-frequency (rf) atmospheric pressure glow discharge. Modulating the plasma makes it possible to successfully prepare porous TiO2 films. We study the trapping of the particles in the sheath during the plasma-on phase and compare it with numerical simulations. During the plasma-off phase, the particles are driven to the substrate by the electric field generated by residual ions, leading to the formation of porous TiO2 film. Using video microscopy, the collective dynamics of particles in the whole process is revealed at the most fundamental kinetic level.
Self-organized patterns of spots on a at metallic anode in a cylindrical glow dis- charge tube are simulated self-consistently. A standard model of a glow discharge is used, comprising conservation and transport equations for a single species of ion and electrons, written with the use of the drift-diffusion and local-field approximations, and the Poisson equation. The computation domain is the region from the anode to the discharge column; only processes in the near-anode region are considered. Multiple solutions, existing in the same range of discharge current and describing modes with and without anode spots, are computed by means of a stationary solver. The computed spots exhibited unexpected behavior. A reversal of the local anode current density in the middle of each of the spots was found, i.e. mini-cathodes are formed inside the spots. The solutions do not fit into the conventional pattern of self-organization in bistable nonlinear dissipative systems; e.g. the modes are not joined by bifurcations.
In order to break the limitation of plasma nitriding technology,which can be applied to a few nonmetallic gaseous elements, the Double Glow Discharge Phenomenon was found and then invented the Double Glow Plasma Surface Metallurgy Technology. This double glow plasma surface metallurgy technology can use any element in the periodic table of chemical elements for surface alloying of metal materials. Countless surface alloys with special physical and chemical properties have been produced on the surfaces of conductive materials.By using double glow discharge phenomenon,a series of new plasma technologies,such as the double glow plasma graphene technology, double glow plasma brazing technology,double glow plasma sintering technology, double glow plasma nanotechnology,double glow plasma cleaning technology, double glow plasma carburizing without hydrogen and so on, have been invented.A very simple phenomenon of double glow discharge can generate about 10 plasma innovation technologies, which fully shows that there is still a lot of innovation space on the basis of classical physics.This paper briefly introduces the basic principles,functions and characteristics of each technology. The application prospects and development directions of plasma in metal materials and machinery manufacturing industry will also be discussed.
The new results concerning neutron emission detection from a laboratory high-voltage discharge in the air are presented. Data were obtained with a combination of plastic scintillation detectors and $^3$He filled counters of thermal neutrons. Strong dependence of the hard x-ray and neutron radiation appearance on the field strength near electrodes, which is determined by their form, was found. We have revealed a more sophisticated temporal structure of the neutron bursts observed during of electric discharge. This may indicate different mechanisms for generating penetrating radiation at the time formation and development of the atmospheric discharge.
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