Abstract
Experimental study of the rates of plasma-chemical deposition of diamond-like coatings in toluene vapour in capacitive RF discharge was carried out. It is shown that in the RF power range of ...100-300 W, the deposition rate is mainly affected by the toluene pressure in the vacuum chamber. The maximum deposition rate obtained was 4.15 μm/h.
The article presents the results of an experimental study of the characteristics of a low-power helicon ion source. Particular attention is paid to the parameters of the particle flow emerging from ...the source and the possibilities for increasing ion energy. It was found that the voltage drop at the output of the source is small (10–15 V), and the main voltage drop is localized at the grounded elements. The ion flux density non-monotonically depends on the magnetic field, while the ion energy remains constant. Applying a constant voltage to the additional electrode inside the discharge chamber does not increase the potential drop at the output of the source. Switching to a lower operating frequency or narrower output orifices allows increasing ion energy, but leads to a decrease in ion flux. At the exit from the source, in the presence of a magnetic field, a directed flow of electrons was detected, the energy of which increases significantly with increasing magnetic field induction. The presence of wave processes in the discharge chamber, which may be responsible for the appearance of an accelerated electron flow, has been demonstrated.
•Directional electron flow from the helicon source was detected.•Only small part of ion accelerating potential is localized at the source exit.•Significant increase in ion energies is required to improve the energy efficiency.•Combination of helicon and DC discharge is considered.
The paper presents the results of an experimental study of the axial structure of the longitudinal RF magnetic field and parameters of the plasma of an inductive low-power plasma source placed in a ...magnetic field of 12–72 G. It is shown that, already in a magnetic field of 24 G, a nonmonotonic dependence of the longitudinal component of the RF magnetic field on the axial coordinate is clearly manifested. The change in the phase of the RF field indicates that a partially traveling wave is formed in the discharge. Probe measurements show that the electron energy distribution function is enriched with fast electrons whose velocity correlates with the phase velocity of the wave.
A pulsed RF discharge is considered experimentally as a working process of an RF ion source. It is shown that an increase in the ion current can be obtained in comparison with the continuous ...operation mode when such a discharge is operating. This increase is the greater, the greater the difference between the characteristic time of the drop of the ion current after turning off the RF power and the rise time of the ion current when the RF power is turned on. The pulsation parameters at which the ion current is maximized are estimated. It is shown that an external constant longitudinal magnetic field in the range of 0–7.2 mT nonmonotonically affects the maximum and equilibrium value of the ion current in a pulse and does not affect the decrease rate of the ion current after the RF power is turned off.
The dependence of the average energy of ions at an output from a radio-frequency plasma source with the geometry of a plasma accelerator with closed electron drift has been experimentally ...investigated. It has been shown that the area of existence of a radio-frequency discharge is wider in comparison with the direct current mode. If the discharge circuit does not allow passage of direct current, the average ion energy varies in the range of 40–90 eV. Using an open for DC discharge circuit results in an increase in the average ion energy ε up to 150–340 eV. Out of three investigated working gases (Kr, Ar, Air), the highest values of ε have been obtained using Kr, the lowest values of ε are typical for the discharge in air.
•RF capacitive discharge in PACED can be ignited and maintained at lower pressures than the DC one.•The flow of accelerated ions is observed downstream the plasma source channel.•The average ion energy varies in the range of 40–90 eV in case of an open DC circuit.•Using a closed DC circuit results in an increase in the average ion energy up to 150–340 eV.•Utilization of argon and air as working gases leads to a decrease in the average ion energy.
The axial distribution of the plasma potential, electron density and temperature in a capacitive RF plasma source with the geometry of an accelerator with a closed electron drift is studied ...experimentally. Two cases of the external electrical discharge circuit are considered. In the first case, the electrodes are closed by direct current, and in the second case, they are open. It is shown that direct current closure of the electrodes leads to a significant increase in the plasma potential and electron density. In a number of cases, local maxima of temperature and plasma density are observed near the electrodes, which can be associated with the occurrence of the azimuthal electron drift in crossed electric and magnetic fields.
The present work aims to analyze the mutual influence of channels in a combined discharge based on the RF inductive and DC discharges and to find the conditions under which the gain in the plasma ...density can be obtained. A cylindrical plasma reactor with a diameter of 20 cm and a length of 20 cm has been used as an object of research. The measurements have been carried out in argon at pressures of 0.08 and 8 Pa, as well as in air at pressures of 8 and 18.7 Pa. The performed experiments have shown that the gain in plasma density in the combined discharge is possible under conditions when the plasma density in DC discharge overcomes that in the inductive one. As a rule, such situation occurs when inductive discharge is in a E-mode. Due to the higher value of the plasma density, provided by the DC channel, the RF power input through the inductive discharge increases. A synergistic effect appears, and the resulting plasma density exceeds the sum of the densities, specific to the inductive and DC discharges separately.
•The gain in plasma density in the combined RF and DC discharge can be obtained.•A synergistic effect appears when the resulting plasma density exceeds the sum of the densities, characteristic of the inductive and DC discharges separately.•The DC channel can be locked in the combined discharge.•The properties of the combined discharge are close to that in the inductive one near antenna and to DC discharge near the cathode if the electron mean free path is smaller than the distance between antenna and electrodes.
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The paper presents the results of an experimental study of a low-power RF inductive plasma source placed in a longitudinal magnetic field. The measurements show the formation of an ion-accelerating ...potential drop at the source output with its value depending on the magnetic field and the flow rate of the working gas. The parameters of the electron and ion flows generated by the source nonmonotonically change with the magnetic field. In the main range of the studied magnetic fields, the electron flux generated by the source at the axis of the system exceeds the ion flux, and the average electron energy increases with the magnetic field.
This paper presents the results of an experimental study of inductive RF ion thruster prototype parameters, which have demonstrated a strong dependence of the prototype characteristics on the length ...of the gas-discharge chamber and the operational frequency of the RF generator. The best result was obtained when the prototype was operated at a frequency of 4 MHz with a gas-discharge chamber 5 cm long. The experiments demonstrated that there is a significant resource for improving thruster parameters associated with an increase in the fraction of the RF power absorbed by the plasma. The latter can be achieved by superimposing an external magnetic field on the discharge. In parallel with the results of the experiments, this paper presents numerical calculations based on the model taking into account the presence of a parasitic capacitive channel of the RF power input into the discharge, as well as power losses in the external circuit. Calculations have shown that the experimentally observed effects are associated with the effect of the capacitive RF power input channel, as well as the frequency dependence of the plasma's ability to absorb the RF power.
•Ion current strongly depends on gas discharge chamber length and operating frequency.•Parasitic capacitive channel is one factor responsible for frequency dependencies.•Another factor is plasma's ability to absorb radio-frequency power.•Efficiency requires maximization of power fraction absorbed by plasma.•This fraction can be increased by imposing external magnetic field on the discharge.
The parameters of a radio-frequency capacitive discharge confined in a closed electron drift accelerator with an extended acceleration zone have been studied for different discharge circuits, namely, ...with dc-closed and dc-open electrodes and with additional dc biasing of the active electrode. In the open circuit, the plasma concentration is minimal and the ion energy in the jet at the exit from the prototype is about 25 eV. The dc closing of the active electrode increases both the plasma density and the ion energy to 250 eV. A further increase or decrease in these parameters is possible by applying a positive or negative dc bias, respectively, to the active electrode.
