Building Langmuir Probes and Emissive Probes for Plasma Potential Measurements in Low Pressure, Low Temperature Plasmas

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.

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An asymptotic preserving well-balanced scheme for the isothermal fluid equations in low-temperature plasmas at low-pressure

Journal of Computational Physics ◽

10.1016/j.jcp.2020.109634 ◽

2020 ◽

Vol 419 ◽

pp. 109634

Author(s):

A. Alvarez Laguna ◽

T. Pichard ◽

T. Magin ◽

P. Chabert ◽

A. Bourdon ◽

...

Keyword(s):

Low Temperature ◽

Low Pressure ◽

Asymptotic Preserving ◽

Fluid Equations ◽

Isothermal Fluid ◽

Low Temperature Plasmas

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Obtaining the unperturbed plasma potential in low-density, low-temperature plasmas

Plasma Sources Science and Technology ◽

10.1088/1361-6595/abef1b ◽

2021 ◽

Author(s):

Federica Causa ◽

Gabriele Gervasini ◽

Andrea Uccello ◽

Gustavo Granucci ◽

Daria Ricci ◽

...

Keyword(s):

Low Temperature ◽

Plasma Potential ◽

Low Density ◽

Low Temperature Plasmas

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Field ion microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104236 ◽

1988 ◽

Vol 46 ◽

pp. 434-435

Author(s):

Gert Ehrlich

Keyword(s):

Low Temperature ◽

Sample Surface ◽

Low Pressure ◽

Radius Of Curvature ◽

Field Ion Microscopy ◽

Phosphor Screen ◽

Ion Microscopy ◽

Field Ion Microscope

The field ion microscope, devised by Erwin Muller in the 1950's, was the first instrument to depict the structure of surfaces in atomic detail. An FIM image of a (111) plane of tungsten (Fig.l) is typical of what can be done by this microscope: for this small plane, every atom, at a separation of 4.48Å from its neighbors in the plane, is revealed. The image of the plane is highly enlarged, as it is projected on a phosphor screen with a radius of curvature more than a million times that of the sample. Müller achieved the resolution necessary to reveal individual atoms by imaging with ions, accommodated to the object at a low temperature. The ions are created at the sample surface by ionization of an inert image gas (usually helium), present at a low pressure (< 1 mTorr). at fields on the order of 4V/Å.

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