Modelling a Langmuir probe in atmospheric pressure plasma at different (original) (raw)
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Determination of the electron density in current-less argon plasma using Langmuir probe measurements
Vacuum, 2004
Langmuir probe measurements were performed in a specially designed D.C. discharge tube with coaxial electrodes in argon current-less plasma (gas pressure 60-130 Pa, discharge current 80 mA). It is well known, that the Langmuir probe yields reliable and easy to interpret results only in the case of low gas pressure. In the case of relatively high pressure, when one cannot neglect the finite probe radius and the effects of collisions in the probe sheath, the probe data used to determine the electron energy distribution function (EEDF) are distorted. In this report, we present the results produced by a computer code that solves the integral equation connecting the experimental second derivative data at relatively high pressure with the real EEDF. r
PIC-MCC Model of a Plasma in the Vicinity of a Cylindrical Langmuir Probe
Contributions to Plasma Physics, 2006
A full kinetic model of an argon plasma in the vicinity of a cylindrical Langmuir probe is developed and presented. The model is one-dimensional in the radial direction and three-dimensional in velocity space. The model simulates the plasma transition from the bulk to the probe surface and particle collection by the probe. Monte Carlo particle-neutral collisions are considered in the model to account for collisional effects on the probe particle collection. Particles are loaded at the plasma bulk boundary with Maxwellian velocity distribution functions. The model output includes space potential and particle density profiles as a function of radius. The model also reproduces typical Langmuir probe current-voltage characteristics at different pressures, plasma parameters and probe dimensions. Modelled electron and ion currents at different pressures for similar plasma parameters are presented, analysed and compared.
2017
This research paper focuses on the study of Spherical Langmuir Probe I-V characteristics in Maxwellian space plasma. This work is conducted using computational techniques to create the exact plasma conditions of the experimental testing environments. The investigations address the development of a technique to model Maxwellian plasma. Three different sized Langmuir probes has been designed theoretically for ionospheric temperature 0.5eV, with the help of computational techniques; I-V traces are produced to analyze the plasma parameters. The variation of floating potential due to probe size is clearly depicted. A manifest trail in the I-V curves is the bump that occurs right after the floating potential. This feature in the transition region affects ability to determine the electron temperature, ion saturation current and plasma potential.
Ion Source Plasma Parameters Measurement using Langmuir Probe
2019
In this work, we present the experimental results of plasma parameters using a Freeman type ion source, such as electron number density ne, plasma electron temperature Te, floating potential Vf, and plasma potential VS. The measurements of these basic parameters of pure Ar plasma were done with a cylindrical Langmuir probe situated perpendicular to a relatively weak magnetic field, B = 20 mT and were performed under constant low Ar pressure 4.6 × 10 mbar. Different methods were implemented to calculate the electron and ion densities. We have concluded that some of these methods are subjected to significant inaccuracy, mainly due to the uncertainty of the plasma potential location. However, It has been recognized that the plasma ion density ni = 1.46 × 10 m found in this experiment using the ion current saturation part is the most reliable among the other values found, using the standard procedures from the electron retardation region (classic Langmuir method) and the electron satura...
Computational technique for plasma parameters determination using Langmuir probe data
Plasma Physics Reports, 2011
In the present work, we consider a new numerical method for processing the experimental infor mation on the electron energy distribution function obtained with a Langmuir probe in a low pressure plasma. This method offers the possibility to establish the temperature and concentration of the electrons for different forms of the distribution function. Some specific difficulties of the previous methods used to do such estimations are surpassed using the method proposed in this work.
Theoretical Study of Spherical Langmuir Probe in Maxwellian Plasma
The Langmuir Probe is the key plasma diagnostic used by scientists interested in plasma characterization to measure the internal parameters of the bulk of the plasma. Spherical Langmuir Probes have been installed on satellites and sounding rockets to observe the general characteristics of thermal plasma in the ionosphere for more than five decades. Because of its simplicity and convenience, the Langmuir probe is one of the most frequently installed scientific instruments on spacecraft. This research explores the theoretical study of Spherical Langmuir Probe I-V Characteristics. With the help of the (volt–ampere curves) of spherical Langmuir probes, the different parameters of plasma can be determined such as plasma potential, floating potential, probe currents in different probe voltage and so on. The effect of electron temperature on the Electron Energy Distribution Function (EEDF) was also analyzed. At higher energy range, the shape of the distribution recovers and the tail trend with energy is maintained and decreases exponentially.
Contributions to Plasma Physics, 2013
The paper reports results from Langmuir probe current-voltage (IV) characteristic measurements in argon and oxygen low-gas-pressure magnetized plasma. The plasma was produced in a stainless steel discharge tube with length 1.5 m and diameter 0.17 m with a hot filaments cathode. The wall of the discharge tube was grounded. An axial magnetic field B was created by a solenoid. A platinum cylindrical Langmuir probe with radius R = 5•10 −5 m and length L = 5• 10 −3 m was placed axially and radially at the center of the discharge tube in order to perform measurements along and across the magnetic field. Using the second derivatives of the measured IV probe characteristics, the EEDF in argon and oxygen was evaluated. The derivatives were taken numerically. Measurements in an argon (i.e., in the absence of negative ions) were performed to obtain results for comparison with the measurements in an oxygen gas discharge, where a high density of negative ions is expected. In the measurements of the second derivatives of the IV characteristics with the probe parallel to the magnetic field in oxygen, a peak appears close to the plasma potential due to the registration of negative ions. In the same time, the electron part of the second derivative was substantially suppressed relatively to the case with the probe oriented perpendicular to the magnetic field. Thus using the appropriate orientation of the probe and a low magnetic field, when the electron part of the second derivative is suppressed, since the negative ion part is not affected by the low magnetic field applied, we can evaluate precisely the negative ion density. The results from the plasma parameters evaluation (plasma potential, electron and negative ion densities and electron temperatures) are presented and discussed.
Plasma parameters measurements by means of Langmuir probe
Radiation Effects and Defects in Solids, 2008
The Langmuir probe (LP) diagnostics is a powerful method for the evaluation of the plasma resistivity curve (I-V curve) and the characterization of the following plasma parameters: electron temperature, electron density, ion density, and plasma potential. In presence of a stable plasma it is possible to extrapolate the electron energy distribution function of the plasma electron population. Because of the long acquisition time (in the order of hundreds of msec or more), this method is suitable for cw plasmas in thermal equilibrium for which the physical properties vary in a time scale longer than the acquisition time. At INFN-LNS the LP diagnostics has been used in order to characterize the TRasco Intense Proton Source plasma, and the low temperature -high density plasmas of a plasma reactor designed for complex molecules dissociation. In the first case, it has been possible to evaluate the plasma properties for different magnetic field profiles and for several operating conditions. In the second case, the LP has permitted to characterize the plasma properties of the plasma reactor at different microwave powers and gas pressures, with the aim to find the optimal experimental conditions in terms of rate of molecules dissociation and of plasma stability and reliability. These series of measurements are here reported, together with measurements of the plasma reactor parameters. Finally, some considerations about the possibility to extend the LP diagnostics to the non-equilibrium plasmas in pulsed mode, as the plasmas obtained by means of laser ablation of solid targets, are given; the design of a possible experimental set-up is outlined.
Contributions to Plasma Physics, 1995
We have carried out Monte Carlo simulation of the motion of Ar+ ions in the space charge sheath surrounding a cylindrical Langmuir probe. From these simulations the percentage of ions crossing the sheath boundary that are collected by the probe have been determined and thus the ion currents to the probe have been calculated. It is shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory and that the exponent, x, of the power law dependence, i , -U > of the ion current, i,, on the probe voltage, Up, increases above the value 0.5 predicted by OMLC theory. The results of the simulations are compared with recent Langmuir probe measurements made in flowing afterglow plasmas.
Langmuir Probe Diagnostics for Medium Pressure and Magnetised Low-Temperature Plasma
Le Journal de Physique IV, 1997
In this contribution we aim at presenting the overview of the work that has been done in expanding the applicability of the probe method to low-temperature plasma at the pressure range when the collisions of charged particles with neutrals start to be important (we call this pressure range medium pressures) and to plasma under the influence of the weak-to-medium magnetic field that is commonly used in plasma enhanced technologies. Most of the discussion is devoted to simple case of a plasma consisting of electrons and of one kind of positive ions. Our review also mostly concerns the cylindrical Langmuir probe. The first part of the article is devoted to discussion on the influence of the positive-ion-neutral collisions on the interpretation of the ion current part of the probe characteristic in order to get the true value of the plasma number density. In the second part one of the theories that take account of this effect is used to assess the influence of the weak magnetic field to the interpretation of the probe data. Finally we discuss the anisotropy of the electron velocity distribution function due to the effect of the magnetic field. The discussion is supported by the new experimental data.