МОДЕЛЮВАННЯ ДУГОВОГО РОЗРЯДУ НА МІДНОМУ КАТОДІ ДЛЯ ГЕНЕРАЦІЇ НАНОСТРУКТУР

The paper considers the model of processes acting in the ionization layer of the cathode assembly during plasma generation of nanostructures. In the given model the processes in electrodynamic and gas - dynamic layers of plasma and their coordination are rather densely considered. Therefore, the solution of the model allows to adequately determine the magnitude of the cathode potential jump in the electrodynamic layer, which allows to compensate for all energy losses during the generation of nanostructures, and the magnitude of ion and electron fluxes at the cathode. The calculations were performed at a constant value of the elongation of the ionization layer, because it has little effect on the change in the ion current density along the length of the cathode layers. Also, the calculations confirmed a non-significant dependence of the initial pressure from the ionization layer on the temperature of the electrons. The obtained dependences, the fraction of ionic current at the cathode and the cathode potential drop from the current density at different cathode temperatures, showed that the change in the proportion of ionic current makes it possible to compensate for energy costs to maintain the cathode temperature. And consideration of the equation of energy balance allowed to establish the range of losses of the working fluid at which it is possible not to take into account the energy of evaporation of the working fluid and steam heating. To determine the current density at the cathode, the dependence of the thermoemission current on the cathode temperature and the dependence of the current density on the cathode on the plasma concentration at different cathode drops and different representations of electric field strengths were obtained. This allowed to determine the cathode temperature due to the ionic current density and to estimate the plasma concentration. Depending on the plasma concentration, the electric transfer coefficient for different emission mechanisms and cathode drops is obtained. All this allowed us to determine the dependence of the specific gravity leaving the cathode per unit time per unit area, on the cathode temperature and heat flux density for the copper cathode. Determining the specific gravity and the transfer coefficient makes it possible to determine the life of the cathode during plasma generation of nanostructures.

Влияние вида функции распределения электронов в плазме и дисперсии по энергии электронного пучка на устойчивость низковольтного пучкового разряда

Within the framework of the kinetic approach, the conditions for the loss of stability of a low-voltage beam discharge in inert gases (LVBD) are studied depending on the temperature of the electron beam, the dispersion of the electron beam velocity in the direction of the discharge axis, and the form of the electron energy distribution function (EEDF). Regimes are considered when the interelectrode distance is on the order of the electron mean free path relative to elastic collisions with inert gas atoms. It is shown that the beam temperature Tb, determined in the LVBD by the cathode temperature not exceeding 1500 K, and the dispersion of the beam electron energy, which in the LVBD can be significantly higher than kTb and reaches 1 - 2 eV, have little effect on the conditions for the loss of stability of the LVBD and the magnitude of the growth rate of disturbance amplification at frequencies up to plasma It was found that the form of the EEDF monotonically decreasing with increasing electron energy also does not affect the parameters of the perturbations propagating in the LVBD at the beam energy much higher than the average electron energy in the plasma. The results obtained are applicable not only to LVBD, but also to other types of self-sustained beam discharges.

A Novel SOFC Thermal Management Strategy of SOFC-GT Hybrid System With Anode and Cathode Control Loops

The SOFC performance and lifetime highly depend on the operation condition, especially the SOFC operation temperature. The temperature fluctuation causes thermal stress in electrodes and electrolyte ceramics. On the other hand, it also needs to maintain a sufficiently high temperature to enable the efficient transport of oxygen ions across the electrolyte. Therefore, it is necessary to design an effective SOFC temperature management system to guarantee safe and efficient operation. In this paper, a two-side temperature control method is proposed to avoid the temperature difference between anode and cathode. Therefore, the SOFC thermal management system includes two control loops. The anode inlet temperature and cathode inlet temperature are controlled by blowers adjusting the recirculated flow rate. In addition, the control performance of the proposed SOFC thermal management system is compared with one-side temperature control systems. The results show that both anode control loop and cathode control loop are essential to get a better control performance. The SOFC would operate with less efficiency with only anode temperature control. On the other hand, the safety problem would occur with only cathode temperature control. The temperature gradient would be more than the upper limit at a part load condition. Therefore, the SOFC thermal management strategy with anode and cathode temperature control loops is feasible for the SOFC-GT system.

Влияние усиленной электрическим полем термической электронной эмиссии на температуру катода с тонкой диэлектрической пленкой в дуговом газовом разряде

A model of thermal electron emission enhanced by the electric field (thermo-field emission) from the metal cathode substrate into a thin insulating film formed on its surface is developed. A system of equations for the cathode surface temperature in the arc discharge and the electric field strength in the film, providing the required discharge current density, is formulated. It is shown that existence of the dielectric film can result in a considerable reduction of the cathode temperature in the discharge due to lower potential barrier height at the metal-insulator boundary than at the metal-discharge boundary in case of the metal cathode without the film. It is found that due to an enhancement of thermal emission of electrons into the film by the electric field generated in it, an additional decrease of the cathode temperature by about 100 K takes place.

Токоперехватывающие сетки из анизотропного пиролитического графита в электронных пушках с металлопористым катодом

Presented the results of experimental researches of anisotropic pyrolitic graphite application as a grid structure in high-power devices with the dispenser cathode. The emission characteristics of molybdenum, hafnium and anisotropic pyrolitic graphite in diodes and electron guns versus high-power electron flow, dissipated on test specimen and cathode temperature are given in the article. Also the grid structures made of anisotropic pyrolitic graphite are able to dissipate power of the electron flow 20 times more than grids made of molybdenum and 9 times more than grids made of hafnium without occurrence of spurious thermionic emission are shown in the article.