Langmuir probe characteristics in a high pressure plasma in the presence of convection and ionization

Clements, R. M.; Rizvi, Abbas H.; Smy, P. R.

doi:10.1109/27.310652

Cited by 11 publications

(14 citation statements)

References 9 publications

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“…[16][17][18] A simple calculation using a particle number density of 10 13 cm Ϫ3 and a Coulomb collision cross section of 10 Ϫ12 cm 2 for singly charged species at a temperature of 0.5 eV, 19 typical of our experimental conditions 5 cm from target, shows that the Langmuir probe operates under collisionless-sheath conditions, where it has been shown that the I/V characteristics of a Langmuir probe can be approximated to those of a static, nonflowing plasma, provided the root-mean-square thermal electron velocity, v rms , in the vicinity of the probe is at least three times greater than the local flow velocity, v f . 16 It can be shown that the ratio R ϭv rms /v f is approximately invariant in time at a given position in a flow resulting from a self-similar, adiabatic expansion and is given by Rϳ(/s)ͱ(3kT e )/m e , where s is the distance of the probe from the source of the expansion, , is the arrival time of plasma at the probe, and T e is the electron temperature of the plasma ͑assumed isothermal͒ at this time.…”

Section: Probe Theoriesmentioning

confidence: 99%

The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes

Weaver

Martin

Graham

et al. 1999

Review of Scientific Instruments

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Section: Probe Theoriesmentioning

confidence: 99%

The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes

Weaver

Martin

Graham

et al. 1999

Review of Scientific Instruments

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“…Simple in principle, the interpretation of the data it provides is rather complicated, because no simple and comprehensive underlying theory exists. Up to relatively recent years, Langmuir probes have been limited to collisionless plasmas and to ion current collection, but in more recent years they have been successfully applied to the characterization of (i) "denser" (higher pressure) plasmas where the effect of collisions become dominant [72,73], and (ii) "higher" degree of ionization (non weakly-ionized plasmas) [74,75] or (iii) of systems in which the plasma flow must be considered [76][77][78], possibly considering the cooling effects on the measured parameters [77,79]. Also, the extension to the collection of electronic currents has been developed in the last decade [80], [81].…”

Section: Introductionmentioning

confidence: 99%

“…The book by Swift and Schwar [65] underlines the difficulties when dealing with "high" pressure plasmas, where the effect of collisions makes the interpretation of the characteristic curve rather involved if not impossible [86]. Furthermore, the impressive number of publications by Clements and Smy [78,79,82,91,[111][112][113][114][115][116][117] while apparently covering a broad range of experimental conditions, are mostly limited to the study of flame plasmas. These are characterized by electron temperatures varying from 1,500 K to 3,000 K, and in which the electron density does not exceed 10 18 m -3 , some four orders of magnitude below the regimes dealt with in this work, although Smy [84,118], and Smy and Noor [118], mention charge density up to 10 20 -10 23 m -3 .…”

Section: Introductionmentioning

confidence: 99%

A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

Fanara

Richardson

2001

J. Phys. D: Appl. Phys.

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The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and "Nonidealities" like cooling due to plasma-probe motion and probe emission mechanisms are then described.The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of 'high' pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this 'cooling' is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.on floating and plasma potentials and estimates of the sheath voltage are made, which are then compared with the results of Chapter 4. Chapter 13 deals with further 'electrical' parameters (current densities, electric field and electrical conductivity). In Chapter 14 several experimental results are presented together in order to gain a unified picture of the resulting arc structure and some observations about possible conduction structures within arcs are made. Finally Chapter 15, after a summary of the whole work, reports the conclusions obtained and suggests further investigations.

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“…These included, for example, the work of McLathy and Smith [9] concerned mainly with the effect of flowing plasma and that of Clements, Smy et al [10,11], who performed a detailed analysis of the effect of the flame plasma density on the measured currents of various charged particles and who were concerned with the specific properties of the plasma sheath in the flame. These included, for example, the work of McLathy and Smith [9] concerned mainly with the effect of flowing plasma and that of Clements, Smy et al [10,11], who performed a detailed analysis of the effect of the flame plasma density on the measured currents of various charged particles and who were concerned with the specific properties of the plasma sheath in the flame.…”

Section: Introductionmentioning

confidence: 99%

“…Several important works were published in the nineteen nineties, dealing in detail with single probe measurements in a flame and describing new theoretical approaches. These included, for example, the work of McLathy and Smith [9] concerned mainly with the effect of flowing plasma and that of Clements, Smy et al [10,11], who performed a detailed analysis of the effect of the flame plasma density on the measured currents of various charged particles and who were concerned with the specific properties of the plasma sheath in the flame. The theory of saturated currents was studied, for example, by Benilov and Rogov [12].…”

Section: Introductionmentioning

confidence: 99%

Electron Temperature Measurement in a Premixed Flat Flame Using the Double Probe Method

Wild

Kudrna

Tichý

et al. 2012

Contrib. Plasma Phys.

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Key words Double probe method, electron temperature, atmospheric premixed flame, flat flame.The electron temperatures Te were measured using a double probe in a premixed methane flame produced by a calibration burner according to Hartung et al. The experiment was performed at atmospheric pressure. In contrast to other authors, we have managed to find typical nonlinearities corresponding to the retarding electron current region and to calculate electron temperatures using a suitable fit on the basis of the measured characteristics. A Pt-Rh thermocouple was used to measure temperatures T h corresponding to "heavy" species.Our results indicate that the flame plasma can be considered to be weakly non-isothermic -Te = (2400 -4000) K, T h = (1400 -1600) K. On the basis of measurement of the saturated ion current, the number density of the charged particles was estimated at (0.3 -3.8)·10 17 m −3 . The trends in Te and T h in dependence on the positions of the probes and thermocouple in the flame differ substantially; this fact has not yet been explained.

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Langmuir probe characteristics in a high pressure plasma in the presence of convection and ionization

Cited by 11 publications

References 9 publications

The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes

The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes

A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

Electron Temperature Measurement in a Premixed Flat Flame Using the Double Probe Method

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