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 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 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.
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.
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.
An experimental study of the structure of waves excited in the low-pressure inductive radio-frequency discharge located in the magnetic field with inductance less than 70 Gs was carried out. A plasma ...source consisting of gas-discharge and process chambers was used in the work. The results of the wave structure study showed that a partially traveling wave was excited in the plasma source when a certain threshold value of the induction of an external magnetic field was exceeded and when a metal flange separating the gas discharge and processing chambers was used. It was also noted that the above-mentioned threshold value decreased with an increase in operating frequency. The amplitude and phase profile of the Bz component of the RF wave indicates the presence of waves reflected from the bottom flange and the local minimum of the electron concentration within the junction of the gas-discharge and process chambers.
•A partially traveling wave is excited in the plasma source at certain threshold value of the induction of a magnetic field.•When using a dielectric separation flange, no wave is excited at the frequency of 4 MHz.•At the frequency of 4 MHz, the wave structure is formed with a longitudinal wavenumber n = 2.•At 13.56 MHz a growth of magnetic field is accompanied by an increase in the number of half-wave lengths from 2 to 4.
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.
The properties of an inductive RF discharge placed in a longitudinal external magnetic field with an induction of less than 70 G at frequencies of 2, 4, and 13.56 MHz are studied. The dependences of ...the region of existence of the discharge, the efficiency of the RF power input and the structure of the RF magnetic field on the external magnetic field induction are studied experimentally. The experimental results are compared with calculations based on a previously developed electromagnetic discharge model. It is shown that the local maximum of the plasma density observed at weak magnetic fields is associated with the resonant excitation of waves in the plasma source. The excited wave is close to a transverse helicon at a frequency of 2 MHz, and its properties approach the Trivelpiece–Gould wave at a frequency of 13.56 MHz,.
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.
Experimental study of the plasma parameters in an RF inductive plasma source consisting of gas-discharge chamber and process chamber (GDC and PC) located in the magnetic field with inductance less ...than 70 Gs was carried out. The magnetic field was close to uniform in the PC and divergent in the GDC. The metal or dielectric flange was used as a separating element between GDC and PC. Experiments showed that an increase in the magnetic field at the pressures when the electron mean free path exceeds the longitudinal size of the plasma source and utilization of the operating frequencies of more than 2 MHz led to the formation of radially limited plasma column, which ended at the bottom grounded flange of PC. In this case, the plasma density in the PC became higher than in the GDC. In the area of the metal separation flange, there was a local minimum of the electron density as well as plasma potential, associated with the parasitic capacitive coupling between the antenna and the separating flange. The growth of the magnetic field led to the equalization of the axial potential distribution.
At the operating frequency of 2 MHz, at the pressures at which the electron mean free path is less than the longitudinal size of the plasma source, the electron density as well as the space potential reaches a maximum in the GDC and, as a rule, decreases monotonously toward the PC.
•Axial distribution of plasma density depends on magnetic field value and RF frequency.•Another factor affecting axial distribution is magnetic field configuration.•Parasitic capacitive coupling between antenna and flange affects axial distribution.•The highest plasma density values are obtained at the operating frequency of 4 MHz.
