scholarly journals Influence of the Ion Mass in the Radial to Orbital Transition in Weakly Collisional Low-Pressure Plasmas Using Cylindrical Langmuir Probes

2020 ◽  
Vol 10 (17) ◽  
pp. 5727 ◽  
Author(s):  
Guillermo Fernando Regodón ◽  
Juan Manuel Díaz-Cabrera ◽  
José Ignacio Fernández Palop ◽  
Jerónimo Ballesteros
Keyword(s):  
Free Path ◽  
Debye Length ◽  
Mean Free Path ◽  
Low Pressure ◽  
Plasma Potential ◽  
Ion Current ◽  
Ion Temperature ◽  
Langmuir Probes ◽  
The Relationship ◽  
Positive Ion

This paper presents an experimentally observed transition from the validity of the radial theories to the validity of the orbital theories that model the ion current collected by a cylindrical Langmuir probe immersed in low-pressure, low-temperature helium plasma when it is negatively biased with respect to the plasma potential, as a function of the positive ion-neutral collision mean free path to the Debye length ratio Λ=λ+/λD. The study has been also conducted on argon and neon plasmas, which allows a comparison based on the mass of the ions, although no transition has been observed for these gases. As the radial or orbital behavior of the ions is essential to establish the validity of the different sheath theories, a theoretical analysis of such a transition not only as a function of the parameters Λ and β=T+/Te, T+ and Te being the positive ion and electron temperature, respectively, but also as a function of the ion mass is provided. This study allows us to recognize the importance of the mass of the ion as the parameter that explains the transition in helium plasmas. Motivated by these theoretical arguments, a novel set of measurements has been performed to study the relationship between the Λ and β parameters in the transition that demonstrate that the effect of the ion mean free path cannot be completely ignored and also that its influence on the ion current collected by the probe is less important than the effect of the ion temperature.

Cation mobilities in liquid and supercritical C1–C4 hydrocarbons

1980 ◽  
Vol 58 (14) ◽  
pp. 1490-1494 ◽  
Author(s):  
Norman Gee ◽  
Gordon R. Freeman
Keyword(s):  
Free Path ◽  
Ion Mobility ◽  
Diffusion Coefficients ◽  
Critical Region ◽  
Mean Free Path ◽  
Liquid Viscosity ◽  
Boiling Points ◽  
Rough Approximation ◽  
The Relationship ◽  
Lower Liquid

The relationship between ion mobility and liquid viscosity is commonly expressed as μ [Formula: see text] η−m. In hydrocarbons the value of m tends to be near 1.0 at η > 5 mP, m > 1.0 at ~5 < η < 1 mP, and m < 1.0 at η < 0.5 mP. Thus there is a maximum in a plot of μη against η−1 and Walden's rule (m = 1.0) is only a rough approximation. The decrease of μη as the critical region is approached is accompanied by an increase in the ratio of diffusion coefficients Dmolec/Dion. Ion mobilities in the liquids well below their normal boiling points are chiefly controlled by the fluidity. At higher temperatures and concomitant lower liquid densities and viscosities μη first increases, due to an increasing ion mean free path, then decreases as the critical region is approached, due to the increasing liquid compressibility and consequent electrostriction about the ion.

New low-frequency waves and negative mass instability in dusty plasmas

2010 ◽  
Vol 76 (6) ◽  
pp. 929-937
Author(s):  
D. P. RESENDES ◽  
R. BINGHAM ◽  
S. MOTA ◽  
V. N. TSYTOVICH
Keyword(s):  
Electron Temperature ◽  
Free Path ◽  
Collision Frequency ◽  
Low Frequency ◽  
Mean Free Path ◽  
Sound Waves ◽  
Ion Temperature ◽  
Plasma Particle ◽  
Charging Mode ◽  
Dust Charging

AbstractLow-frequency dusty plasma waves with frequencies much smaller than the frequency of charging collisions of plasma particles with dust particles are considered taking into account elastic and charging collisions of plasma particles with dust and neutrals. The usual dust sound waves with an upper frequency equal to the dust plasma frequency are found to be present only for wavelengths much smaller than the plasma particle effective mean free path due to the effective collision frequency. The effectice collision frequency is found to be inversely proportional to the square root of the product of the charging frequency and the frequency of particle momentum losses, involving processes due to elastic plasma particle–dust collisions and collisions with neutrals. It is shown that when the wavelength of the wave is much larger than the mean free path for effective collisions, the properties of the waves are different from those considered previously. A negative mass instability is found in this domain of frequencies when the effective mean free path of ions is larger than the effective mean free path of electrons. In the absence of neutrals, this appears to be possible only if the temperature of ions exceeds the electron temperature. This can occur in laboratory experiments and space plasmas but not in plasma-etching experiments. In the absence of instability, a new dust oscillation, a dust charging mode, is found, whose frequency is almost constant over a certain range of wave numbers. It is inversely proportional to the dust mass and charging frequency of the dust. A new dust electron sound wave is found for frequencies less than the frequency of the dust charging mode. The velocity of the dust electron sound wave is determined by the electron temperature but not the ion temperature, as for the usual dust sound waves, with the electron temperature substantially exceeding the ion temperature.

Estimation of the Damping in MEMS Inertial Sensors: Comparison Between Numerical and Experimental Results Both at High and Low Pressure Levels

2006 ◽  
Author(s):  
Francesco Braghin ◽  
Elisabetta Leo ◽  
Ferruccio Resta
Keyword(s):  
Viscous Fluid ◽  
Free Path ◽  
Inertial Sensors ◽  
High Vacuum ◽  
Mean Free Path ◽  
Low Pressure ◽  
Ultra High Vacuum ◽  
Squeeze Film ◽  
Working Pressure ◽  
Order Of Magnitude

Except for MEMS working in ultra high vacuum, the main cause of damping is the air surrounding the system. When the working pressure is equal to the atmospheric one (from now on called “high pressure”, i.e. 105Pa), the mean free path of an air molecule is much smaller than typical MEMS dimensions. Thus, air can be considered as a viscous fluid and two phenomena occur: flow damping and squeeze film damping. These two terms can be evaluated through a simplified Navies-Stocks equation. In vacuum (from now on called “low pressure”, i.e. 26Pa), the air cannot be considered as a viscous fluid any more since the free path of an air molecule is of the same order of magnitude of typical MEMS dimensions. Thus, the molecular fluid theory must be used to estimate the damping. To predict the damping of a MEMS device both at high and low pressure levels, a multi-physics code was used and the achieved numerical results were compared to experimental data measured on the same device.

ANISOTROPY OF THE ENERGY GAP IN SUPERCONDUCTING LEAD–BISMUTH ALLOYS

1966 ◽  
Vol 44 (11) ◽  
pp. 2601-2604 ◽  
Author(s):  
C. K. Campbell ◽  
R. C. Dynes ◽  
D. G. Walmsley
Keyword(s):  
Free Path ◽  
Energy Gap ◽  
Mean Free Path ◽  
The Relationship

Tunneling techniques have been applied to a study of the remanent anisotropy of the energy gap in superconducting Pb–Bi alloys. The relationship between anisotropy and mean free path L is discussed for situations in which L is well inside the "dirty" superconductor limit (L ~ ξ0).

The operation of Langmuir probes in electro-negative plasmas

1959 ◽  
Vol 252 (1268) ◽  
pp. 102-119 ◽  
Keyword(s):  
Negative Ions ◽  
Ion Current ◽  
Langmuir Probes ◽  
Negative Probe ◽  
Ion Energy ◽  
Ion Energy Distribution ◽  
Sheath Region ◽  
Sheath Edge ◽  
Positive Ions ◽  
Positive Ion

A criterion that must be satisfied by the positive-ion energy distribution at the edge of a sheath surrounding a negative probe is derived for the case when negative ions are present. This criterion is then used to derive the potential outside the sheath region surrounding a spherical probe immersed in an electro-negative plasma. It is found that the potential falls to low values when the ratio of negative ions to electrons exceeds 2. Under these circumstances the positive-ion current collected is the random current across the sheath edge. If, however, the ratio is much less than 2 then the collection of positive ions proceeds as for an electro-positive gas.

Theoretical ion current to cylindrical Langmuir probes for finite ion temperature values

1996 ◽  
Vol 29 (11) ◽  
pp. 2832-2840 ◽  
Author(s):  
J I Fernández Palop ◽  
J Ballesteros ◽  
V Colomer ◽  
M A Hernández
Keyword(s):  
Ion Current ◽  
Ion Temperature ◽  
Langmuir Probes

Applicability of Child–Langmuir collision laws for describing a dc cathode sheath in N2O

2013 ◽  
Vol 80 (3) ◽  
pp. 319-327 ◽  
Author(s):  
V. A. Lisovskiy ◽  
E. P. Artushenko ◽  
V. D. Yegorenkov
Keyword(s):  
Glow Discharge ◽  
Free Path ◽  
Ion Mobility ◽  
Pressure Range ◽  
Mean Free Path ◽  
Low Pressure ◽  
Correct Description ◽  
Cathode Sheath ◽  
Intermediate Pressure ◽  
The Law

It is established which of the Child–Langmuir collision law versions are most appropriate for describing the processes in the cathode sheath in the N2O. At low pressure (up to 0.3 Torr), the Child–Langmuir law version relating to the constant ion mobility holds. At N2O pressure values starting from 0.75 Torr and above, one has to employ the law version for which it is assumed that the ion mean free path within the cathode sheath is constant. In the intermediate pressure range (between 0.3 and 0.75 Torr), neither of the Child–Langmuir law versions gives a correct description of the cathode sheath of the glow discharge in the N2O.

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