Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF)discharge sustained at low pressures,typical of the operating modes of RF gridded ion sources.The motivation for the study is the question of whether the RF pulsemodulated mode can increase the efficiency of the ion source.The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared.The experimental data were also compared with the parameter calculations based on a0D numerical model of the discharge.The measurements showed that the pulse-modulated operation mode of the RF ion source had a noticeable advantage when the power of the RF generator was 140 W or lower.However,as the generator power increased,the advantage was lost because the pulse-modulated operation mode,having a higher RF power instant value,entered the region of existence sooner than the continuous mode,where the ion production cost begins to grow with RF power.

Power absorption,plasma parameters and wave structure in inductive RF plasma source with low value external magnetic field

The efficiency of radio-frequency(RF)power absorption,RF magnetic field structure and plasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameter and 22,32,53 cm in length with a low value external magnetic field.The experiments were carried out in argon at pressures of 13-140 m Pa.The RF power supply changed from 200 W to 800 W.The spiral antenna was used for sustaining the discharge.It was shown that efficiency of RF power absorption depended nonlinearly on the external magnetic field values.At maximal values of the RF power absorption efficiency,the axial distributions of longitudinal Bzand azimuthal Bφcomponents of RF magnetic field manifested the formation of the partially standing wave with a half wavelength close to 8 cm.At the same conditions,the axial dependence of the radial RF magnetic field component Brdiffered drastically.It was concluded that the Bz and Bφamplitudes were largely determined by the RF field of Trivelpiece-Gould wave,while Br amplitude represented the radial RF field of the helicon wave.

Experimental study of a low-pressure hybrid RF discharge

Experimental study of the low-pressure hybrid RF discharge with both inductive and capacitive channels was carried out. The RF power unit consists of inductor(antenna) and capacitor plates connected in parallel to the same RF power source. A separating capacitor Csepis included into the circuit between the antenna ends and the lead connected to the discharge capacitor plate in order to prevent the closing of the capacitive circuit through direct current by inductor and to control the contribution of capacitive channel to discharge sustaining. It is shown that at low power of the RF power source, power coupling to the discharge mainly occurs through the capacitive channel. Increasing the power of the RF power source increases the power coupled in the inductive channel, electron density, and current flowing through the capacitive channel. This leads to increasing voltage drop on the separating capacitor and partial cutoff of the capacitive channel. At separating capacitance values below certain value(below 50 pF in the present experiments), the self-bias of the loaded plate of the discharge capacitor becomes positive indicating that the thickness of the electrode sheath of the loaded electrode decreases compared to thickness of the sheath of the grounded electrode. The thickness of the space-charge sheath of the grounded electrode decreases with increasing power coupled to the plasma. At separating capacitance below 50 pF, higher harmonics of the RF voltage and current are actively generated in the capacitive discharge channel. Increasing the separating capacitance leads to decreasing electron density, increasing effective electron temperature and more effective RF energy coupling to plasma due to increasing relative importance of the capacitive discharge channel.

Plasma treatment for enhancement of the sorption capacity of carbon fabric

In this work we carried out an experimental investigation into enhancement of the sorption capacity of carbon fabric using plasma treatment methods.Carbon fabric is based on viscose fiber and is hydrophobic by nature.Enhancement of the fabric sorption capacity is required for its application in medicine.For this purpose,two plasma treatment methods were considered,i.e.atmospheric nonequilibrium radiofrequency(RF)discharge and a vacuum RF plasma source with an external magnetic field.Samples treated by atmospheric discharge demonstrated aging effects during the first week after treatment.The sorption capacity of samples treated by the RF plasma source was stable over the same period and reached values as high as 0.95.Parameters of the beam created by the vacuum RF plasma source were analyzed and dependences of the fabric sorption capacity and specific surface area on plasma treatment time were investigated.We found that sorption capacity reached its maximum value after 30 min of treatment and did not change significantly if processing was continued,while the specific surface area reached its maximum after 3 min of treatment and quickly decreased after that.It was found that the micropore structure of the fabric remained almost the same during plasma treatment.The volume of mesopores in a unit of the fabric mass(specific volume)doubled during the first 5 min of treatment and returned to initial values after 30 min of treatment.The sorption capacity continued to increase even when the specific surface area decreased after reaching its peak value.This indicates the important role of surface functional groups formed on carbon fibers during plasma treatment.This is consistent with the results of x-ray photoelectron spectroscopy analysis showing changes in surface oxidation during plasma treatment.