Thin-wire Langmuir-probe measurements in the transition and free-molecular flow regimes

Dunn, Michael G.; Lordi, J. A.

doi:10.2514/3.5834

Cited by 15 publications

(6 citation statements)

References 17 publications

(9 reference statements)

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“…Therefore we concentrated on the effect of collisions on positive-ion collection by a Langmuir probe. This effect has already been studied extensively; examples of earlier papers on this subject are [13][14][15][16][17][18][19][20][21][22]. Qualitatively speaking the effect of collisions on the positive-ion collection is demonstrated in two ways:…”

Section: The Influence Of Ion-neutral Collisions On Probe Measurementsmentioning

confidence: 99%

An experimental study of plasma density determination by a cylindrical Langmuir probe at different pressures and magnetic fields in a cylindrical magnetron discharge in heavy rare gases

Passoth

Kudrna

Csambal

et al. 1997

J. Phys. D: Appl. Phys.

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This article presents an experimental study that contributes to the problem of interpretation of cylindrical Langmuir probe data obtained in a non-isothermal low-temperature plasma in magnetic field. A discussion on the influence of positive ion - neutral collisions on the charged particle density estimation is also given and the effect is demonstrated on the experimental data. A Maxwellian electron energy distribution is assumed throughout the present study. The Langmuir probe data are obtained in a cylindrical magnetron discharge in argon at pressures from 1.5 to 6 Pa and magnetic fields between 100 and 500 G. The radially movable Langmuir probe was made of either m or m diameter tungsten wire in order to investigate the effect of the probe dimensions on the estimated plasma density. The electron density is calculated from the electron current at the space potential (used as a reference) and from the OML collisionless theory. The ion density is calculated by using ABR - Chen theory without and with the correction due to the collisions of positive ions in the probe sheath. Also, the recent collisional positive-ion-collection-theory is used for comparison. The resulting numerical values of plasma density are compared over more than one order of magnitude change in the plasma density given by its radial dependence in the cylindrical magnetron discharge. Optical measurements were made in order to quantitatively assess the neutral gas temperature in the discharge and the density of particles in excited states that could induce secondary electron emission from the probe surface and thus apparently enhance the positive-ion density estimated from the probe positive-ion current. The effect of secondary electron emission from the probe surface on the probe data interpretation has been found small compared to the experimental error limits and consequently not substantial for our experimental conditions. In the range of our experimental conditions the ABR - Chen theory with the collisional correction gives the best agreement of the estimated numerical values of ion and electron densities in the whole range of its investigated change. Also from our results it follows that the effect of the magnetic field on the thinner-probe-electron-current at the space potential and hence on the reference-electron-density-estimation is negligible within the experimental uncertainties up to a magnetic field strength of 500 G which was the maximum used in our experimental study.

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Section: The Influence Of Ion-neutral Collisions On Probe Measurementsmentioning

confidence: 99%

An experimental study of plasma density determination by a cylindrical Langmuir probe at different pressures and magnetic fields in a cylindrical magnetron discharge in heavy rare gases

Passoth

Kudrna

Csambal

et al. 1997

J. Phys. D: Appl. Phys.

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“…5 in Ref. 16 and Fig. 9 in this paper shows an essential resemblance in the variation of the ion current at r p /l D < 1.…”

Section: Probe Response In the Oml Regionmentioning

confidence: 60%

“…On the other hand, the reported results differ between themselves in some respects. 1 ' 11 ' 14 ' 16 It is suggested that at least part of the apparent disagreement can be explained in terms of ion-neutral collisional effects described in this paper.…”

Section: Probe Response In the Oml Regionmentioning

confidence: 80%

“…We note that both the reduction of I t and shifting the experimental points toward lower (r p /l D ) 2 Ii may possibly bring the data not only into an agreement with theory in the OML region but, perhaps, also into an even closer agreement in the "space-chargelimited" region. The latter remark refers to the measurements obtained with probe 16 Their data obtained with aligned probes and assumed to be unaffected by flow velocity extended over a range 0.5 < r p /A D < 2. For r p /A D > 1, the free-molecular probe data compared favorably with theory of Laframboise, but at smaller r p /A D> the probe current was higher than theoretical prediction.…”

Section: Probe Response In the Oml Regionmentioning

confidence: 99%

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Effect of Angle of Incidence on the Response of Cylindrical Electrostatic Probes at Supersonic Speeds

Jakubowski

1972

AIAA Journal

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The response of cylindrical probes at various angles of incidence has been studied in low-density hypersonic argon plasma. All mean free paths were larger than probe radii (r p ) except the ion-ion mean free path which was smaller than r p in most of the tests. In nearly all experiments, an ion current peak has been observed near the zero angle of incidence. The magnitude of this effect is shown to depend strongly on probe radius-to-Debye length ratio (r p /A D ) and is significant for 0.5 < r p /l D < 2. Insensitivity of this effect to probe length appears to be closely related to the presence of ion collisions. A physical model is proposed which explains the effect in terms of ionneutral collisions in the presheath of the probes. A simple theory is presented in the paper which attempts to account for the measured data on the ion current peak. The readings obtained with aligned and transverse probes are interpreted using collisionless theories (Laframboise, Smetana, modified Langmuir) and the current vs angle-ofattack variation is used to infer "collision-free" value of the ion current to aligned probes. The experimental results appear to agree with Laframboise's theory in the orbital-motion-limited region. Disagreements with theory reported by several investigators can be explained either in terms of ion-neutral collisions associated with aligned probes (in "nearly collisionless" plasmas) or in terms of an end effect (in highly rarefied plasmas).

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“…and the probe length / was 0.4 in., affording an l/D ratio of 100. Previous studies 25 have demonstrated no dependence on the derived electron temperature or number density on the fineness ratio, I/D at l/D values down to 50.…”

Section: Details Of the Measurementsmentioning

confidence: 95%

Experimental and Numerical Studies of Flush Electrostatic Probes in Hypersonic Ionized Flows: I. Experiment

Boyer

Touryan

1972

AIAA Journal

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Experimental studies were performed to determine the ion current collection characteristics of flush-mounted electrostatic probes on a sharp flat plate in ionized hypersonic flows. The effects of probe size, geometry, position, bias, and local flow properties were explored. The probe current densities measured in nitrogen, argon, and carbon monoxide plasmas were correlated in terms of the flow Reynolds number, electron convective flux, probe size, applied potential and electron-to-ion temperature ratio. The correlation predicts well similar data available in the literature. Comparison with a numerical solution of Poisson's equation yields results which validate the correlation. Nomenclature A/A# = nozzle area ratio C* = Chapman-Rubesin constant in the linear viscositytemperature relation D = diffusion coefficient e -electron charge / = probe current J = current density m = exponent in flush-probe current-voltage relationship M = Mach number n = number density p = pressure R = probe radius Re = Reynolds number Sc = Schmidt number T = temperature u = flow velocity V = probe voltage relative to ground x = distance from plate leading edge X N = axial distance from nozzle throat y = distance normal to surface of flat plate P = ratio of ion to electron diffusion coefficient 6 = boundary-layer thickness £ = TJT e K = correlation parameter, (R/A D ) 2 l/Re xo Sc t k = mean free path A 5 = sheath thickness A D = Debye length (in general based on boundary-layer edge conditions) \ JL = viscosity p = density

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Thin-wire Langmuir-probe measurements in the transition and free-molecular flow regimes

Cited by 15 publications

References 17 publications

An experimental study of plasma density determination by a cylindrical Langmuir probe at different pressures and magnetic fields in a cylindrical magnetron discharge in heavy rare gases

An experimental study of plasma density determination by a cylindrical Langmuir probe at different pressures and magnetic fields in a cylindrical magnetron discharge in heavy rare gases

Effect of Angle of Incidence on the Response of Cylindrical Electrostatic Probes at Supersonic Speeds

Experimental and Numerical Studies of Flush Electrostatic Probes in Hypersonic Ionized Flows: I. Experiment

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