Plasma parameters of a small microwave discharge at atmospheric pressure obtained by probe diagnostics (original) (raw)
Related papers
Probe diagnostics in high pressure high density microwave plasma
High pressure helium microwave discharge by the moderate microwave power of 400W has been investigated. A method for the determination of electron temperature and the plasma density by a Langmuir probe is established using Cohen model in the asymptotic limits of DrRy']'"o *@, e=T/Tr-Oand O<tpr<ln(Dl),where Ro,Lo,Dl,T*,T"andgrarctheproberadius,theelectronDebyelength, the Debye numbern ion and electron temperatures and the probe potential normalized by electron energy, respectively. Simple algebraic functions derived from Cohen's results allow one to use iterative procedures for the determination of plasma parameters and avoid making the fitting parameters discrete. The proposed fitting technique allows one to obtain reasonable plasma parameters even for high secondary electron emission currents from the probe. l.Introduction High pressure discharges are of increasing interest for the reactive plasma processingl). There are several convenient features of the microwave excited high pressure non-thermal plasmas. In such plasmas, gas flow rate can be much lower, power transfer from a generator to plasma becomes higher, gas temperature becomes much lower and the electrode contamination is devoid. Additional features are the stability and feasible operation. Microwave discharge can be operated over a wide range of experimental parameters (pressure: from l0-5 Ton up to atmospheric pressure, microwave power: from several watts up to kilowatts, frequency: from l0MHz up to l0GHz), which facilitate to control the plasma in a variety of parameters2). High pressure plasma processing can provide several advantages over low pressure plasma one. There is no need of the equipment for magnetic field generation and high vacuum systems, which can largely reduce the equipment cost. Furthermore, high pressure plasmas enable one to produce large amount of reactive species like ions, excited atoms and free radicals. Therefore, high pressure discharges have been used for gas discharge lasers or the ozone production for water purification3). For plasma source design and discharge performance optimization, good knowledge of plasma parameters and their spatial distributions are required. In order to interpret the data measured under different experimental conditionsa), it is important to have a proper theoretical model, which can provide reliable plasma parameters. The Langmuir probe is a most widely used diagnostic tool for the determination of plasma parameters because it can provide local plasma properties that cannot be obtained by other diagnostic techniques. The pioneer model
Electric probe investigations of microwave generated, atmospheric pressure, plasma jets
Journal of Applied Physics, 2010
We examine the applicability of the Langmuir-type of characterization for atmospheric pressure plasma jets generated in a millimeter-size cavity microwave resonator at 2.45 GHz. Wide range I-V characteristics of helium, argon, nitrogen, air and oxygen are presented for different gas fluxes, distances probe-resonator, and microwave powers. A detailed analysis is performed for the fine variation in the current around the floating potential. A simplified theory specially developed for this case is presented, considering the ionic and electronic saturation currents and the floating potential. Based on this theory, we conclude that, while the charge carrier density depends on gas flow, distance to plasma source, and microwave absorbed power, the electron temperature is quite independent of these parameters. The resulting plasma parameters for helium, argon, and nitrogen are presented.
Spectral measurements in the plasma of microwave and magnetron discharges
Journal of Physics: Conference Series, 2019
Spectroscopic methods were used to study the parameters of a low-power (≤ 100 W) magnetron discharge plasma, as well as a low-pressure microwave discharge (6–40 Pa) in argon. It is shown that in the magnetron discharge the concentration of atoms and ions of the buffer gas (Ar) and the target material (Cu) decreases exponentially with distance from the target cathode and in the first case it occurs much more sharply. The temperature of electrons in a plasma stream, which is emitted by a discharge burning near the surface of the cathode, was estimated from the relative intensity of the spectral lines according to the LTE model and the coronal model. The values obtained in both cases were close, lying near 1 eV, and the temperature remained almost constant with the distance from the cathode. The electron temperature in the microwave discharge turned out to be almost constant over the cross section of the plasma column, while the concentration near the microwave emitter was 2–3 times hi...
Comments on plasma diagnostics with microwave probes
Physics of Plasmas
Analysis of recent publications on microwave probe diagnostics shows that some assumptions used in microwave probe models are unrealistic and ambiguous, which puts into question the validity of those diagnostics.
Probe diagnostics of high pressure microwave discharge in helium
Journal of Applied Physics, 2002
A method for the determination of electron temperature and plasma density in high pressure helium plasmas is established using numerical results of the continuum probe model by Cohen ͓Phys. Fluids 6, 1492 ͑1963͔͒. Simple algebraic functions are derived to approximate the probe characteristics of high pressure plasmas calculated by Cohen and are applied to use iterative procedures for the determination of plasma parameters. The proposed fitting technique has allowed one to obtain reasonable plasma parameters even for the probe characteristics strongly affected by large secondary electron emission currents from the probe. Fitting of the ion saturation current may possibly be used to estimate the ion temperature, provided that the electron temperature and plasma density are known. Finally high pressure helium microwave discharges have been produced by moderate microwave power of 400 W and investigated by the present method.
Probe Diagnostics of Microwave Plasma at Frequency 2.45 GHz in CW and Pulse Regime
Contributions to Plasma Physics, 2006
The paper is focused on diagnostics of newly developed surfatron-based plasma source working at frequency 2.45 GHz. This plasma source of jet type can be operated in cw as well as in PC controlled pulse regime. We carried out diagnostic of the plasma exiting the nozzle by single and double Langmuir probe in cw as well as in pulsed regime of plasma source operation. The basic plasma parameters-electron density and electron temperature-are estimated from single probe measurements at low pressures. The electron temperature in wide range of pressures is evaluated from double probe measurements. Time evolution of electron temperature along a single period in pulsed mode of operation is measured and discussed. The exiting plasma stream is directly applied on a plastic material sample (PE) with the aim to increase its hydrophility. Degree of hydrophility is characterized by contact angle measurements. Relations between process plasma parameters and results of contact angle measurements are discussed.
Physics of Plasmas, 2006
A torch type microwave-induced afterglow plasma was produced at atmospheric pressure using an open-ended fused silica concentric double tube assisted by Ar and O 2 supply gases. The plasma emerged from the end of the discharge tube and was exposed to ambient air. A parametric study of the plasma characteristics was performed by measuring the temperature, density, and plasma volume as the operational parameters such as microwave power, gas flow rate, and its composition were varied. The excitation temperature ͑T exc ͒ obtained from the Ar I emission spectrum ranged from 3010 to 4350 K and the rotational temperature ͑T rot ͒ measured from the OH and O 2 diatomic molecular spectra ranged from 2250 to 3550 K. The electron density ͑n e ͒ from the H  Stark broadening width at the plasma core was in the range of 6.6 to 7.6ϫ 10 14 cm −3. The two-dimensional distribution of T exc and T rot was also obtained. Experiments while varying the Ar and O 2 gas flow rate and the O 2 / Ar ratio showed that n e was reduced but T exc was increased as the O 2 flow rate was increased. Using an additional dielectric tube for shielding the plasma from the ambient air demonstrated a significantly enlarged plasma length and lower T rot due to the nitrogen entrainment, as compared to the unshielded case.
Contributions To Plasma Physics, 2008
We report a study of electron saturation current variations at varying probe heating that were found to be closely related to probe wire contamination. The study was performed in three types of low temperature argon plasma – the weakly magnetized plasma of a cylindrical magnetron, the non-magnetized plasma of a double plasma machine and a hollow cathode plasma jet, showing different trends. In the present work the effect of overestimation of the plasma potential by a strongly emitting probe is discussed and experimental data are compared with a theoretical model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of Simple Designs of Multitip Probe Diagnostic Systems for RF Plasma Characterization
Multitip probes are very useful diagnostics for analyzing and controlling the physical phenomena occurring in low temperature discharge plasmas. However, DC biased probes often fail to perform well in processing plasmas. The objective of the work was to deduce simple designs of DC biased multitip probes for parametric study of radio frequency plasmas. For this purpose, symmetric double probe, asymmetric double probe, and symmetric triple probe diagnostic systems and their driving circuits were designed and tested in an inductively coupled plasma (ICP) generated by a 13.56 MHz radio frequency (RF) source. Using I-V characteristics of these probes, electron temperature, electron number density, and ion saturation current was measured as a function of input power and filling gas pressure. An increasing trend was noticed in electron temperature and electron number density for increasing input RF power whilst a decreasing trend was evident in these parameters when measured against filling gas pressure. In addition, the electron energy probability function (EEPF) was also studied by using an asymmetric double probe. These studies confirmed the non-Maxwellian nature of the EEPF and the presence of two groups of the energetic electrons at low filling gas pressures.