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As a method to optimize the power frequency of dual-frequency plasma, we propose an optimization method that combines genetic algorithm and plasma simulation. A two-dimensional plasma simulation model of Ar plasma was constructed with a fluid model. Combining this simulation model with a genetic algorithm, 300 cases of plasma conditions with high plasma density and small variation in electron density were calculated. As a result, the optimum conditions were 175 to 210 MHz for the high-frequency generator and 1.0 to 2.5 MHz for the low-frequency generator. Furthermore, two types of single objective functions that combine the electron density and the variation rate were proposed. The single objective functions with emphasis on electron density and with emphasis on variation rate were introduced, and each objective function was optimized. [ABSTRACT FROM AUTHOR]

Plasma potential is a key parameter in plasma discharge or fusion plasma to control plasma–wall interaction or ExB drift. The magnitude of plasma potential depends on the overall energy transmitted to the plasma via direct current (dc) or radio frequency (RF) devices such as electrodes or antennas. Knowing the plasma potential from the exciting source is useful to prevent high energetic fluxes to the wall or to improve the plasma confinement or explaining shear velocity. The aim of the present model is to calculate this plasma potential with respect to a dc or RF source in a magnetized or unmagnetized plasma. This double saturated probe (DSP) model takes into account the electron saturation current and is able to derive the plasma potential as a function of the electrode/wall area ratio for a dc or RF discharge in a helium/argon plasma with or without a magnetic field. The results of the model are compared with Aanesland’s model in the case of unmagnetized capacitive sheath and particle-in-cell (PIC) simulations. The magnetized model is applied to a plasma column with a perpendicular capacitive current in an RF discharge. It appears that the plasma potential can increase to almost the RF potential value at a low wall/electrode area ratio ($A_{\text {wall}}/A_{\text {el}}$ lower than 5), while the same potential collapses as soon as the area ratio (perpendicular over the parallel current area) is higher than the electron/ion saturation current ratio. This is directly due to the saturation of electron current, preventing the plasma potential from following the imposed RF potential by the electrode, so that the maximum value can be as lower as the floating potential. The perpendicular current involved is mainly a conduction current modeled as a resistive collisional current. In fusion plasma, the maximum plasma potential can rise to higher values than in plasma discharges, but the collapse of the potential still occurs for long collisional biased flux tubes. [ABSTRACT FROM AUTHOR]

Plasma density in a magnetized, capacitive-coupled, radio frequency (RF) discharge has been determined using the electrical impedance characteristics of the discharge. The effective impedance between the parallel plate electrodes has been treated as an equivalent electric circuit consisting of resistive and reactive components, expressed in terms of high-frequency plasma conductivity. Hence the model is used to connect the externally measured RF voltage, current, and their relative phase to plasma density. Additionally, a triple Langmuir probe (TLP) is used to substantiate the results of the electrical impedance model. The plasma density obtained using the direct probe measurement is found to be in good agreement with those determined from the passive measurements based on electrical impedance of the discharge as outlined in this article. [ABSTRACT FROM AUTHOR]

The fluid model, also called the macroscopic model, is commonly used to simulate low temperature and low pressure radiofrequency plasma discharges. By varying the parameters of the model, numerical simulation allows us to study several cases, providing us the physico-chemical information that is often difficult to obtain experimentally. In this work, using the fluid model, we employ numerical simulation to show the effect of pressure and space between the reactor electrodes on the fundamental properties of silicon plasma diluted with ammonia and hydrogen. The results show the evolution of the fundamental characteristics of the plasma discharge as a function of the variation of the pressure and the distance between the electrodes. By examining the pressure-distance product in a range between 0.3 Torr 2.7 cm and 0.7 Torr 4 cm, we have determined the optimal pressure-distance product that allows better deposition of hydrogenated silicon nitride (SiNxHy) films which is 0.7 Torr 2.7 cm. [ABSTRACT FROM AUTHOR]

The problem of generating a stationary electric field in a magnetized radio-frequency discharge (rf) plasma is studied experimentally. Helmholtz coils produce magnetic field in a cylindrical vacuum chamber with diameter of 85.6 cm and length of 220 cm. RF discharge is generated at a frequency of ~5 MHz. The rf power absorbed by plasma lies in the range 0.5-1.5 kW. Electrodes defining a negative potential are placed at the ends of the chamber. Two pairs of circular flat electrodes with diameter of 5.5 and 45 cm are investigated. The working gas is argon. Radial profiles of electron density and temperature are obtained. Radial profile of the plasma potential is investigated, as well as the dependence of plasma potential on the voltage applied to the end-electrodes. [ABSTRACT FROM AUTHOR]

Microwave plasma was generated on top of the electrode by applying microwave radiation of 2.45 GHz in water. The light-emitting region and radicals formed by microwave discharge were investigated. The experimental results showed that the light-emitting region of microwave plasma in water increased with increasing microwave power, and conversely, decreased with increasing pressure; bubble around the plasma also became small when pressure was enhanced. OH radicals, H atoms, and O atoms were identified using optical emission spectroscopic analysis. The emission intensity of these radicals and atoms increased with increasing microwave power and decreased with increasing internal pressure of reactor vessel. Moreover, the electron excitation temperature of the plasma increased with electric power from 3300 to 4100 K and decreased with pressure from 4300 to 4100 K in comparison with the intensities of \textH\alpha and \textH\beta . [ABSTRACT FROM PUBLISHER]

In order to further improve the hydrogen production efficiency of microwave liquid-phase discharge, a three-electrode reactor was designed and a suspended electrode was added. The internal structure of the three-electrode reactor was optimized. The formation of bubbles during the discharge and the change characteristics of plasma morphology were studied after adding the suspended electrode. In addition to investigating the physical influence of the suspended electrode on the discharge plasma, the influences of the different electrode materials and specific surface area of the suspension electrode on the composition of the gas products, the hydrogen flow rate and the hydrogen energy yield were also investigated. The experimental results show that the suspended electrode can increase the formation time of plasma and bubble. In this study, the highest flow rate of total gas is 29.5 NL/min with the 80 PPI-Cu foamed metal suspended electrode which is an increase of 31.5% than no suspended electrode. • Suspended electrode with high specific surface area is used. • The effect of suspended electrode on bubble residence time is discussed. • The energy yield of hydrogen production increased by 34.6%. [ABSTRACT FROM AUTHOR]