Langmuir Probe Evaluation of the Plasma Potential in Tokamak Edge Plasma for Non‐Maxwellian EEDF

Popov, Tsv K; Dimitrova, M.; Ivanova, P. K.; Hasan, E; Horáček, J.; Dejarnac, R.; Ştöckel, J.; Weinzettl, V.; Kovačič, J.

doi:10.1002/ctpp.201410076

Cited by 22 publications

(31 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Uncertainties depend on probe geometry, probe theory, acquisition system, measurement procedure and data treatment. In this work, the accuracy of the plasma potential is estimated to be around 10 % from a statistical analysis 52 . In the remainder of this section a relative uncertainty of ±50% and ±30% is considered for the electron density and temperature, respectively 53 .…”

Section: Langmuir Probe Resultsmentioning

confidence: 99%

Anode geometry influence on LaB6 cathode discharge characteristics

et al. 2019

View full text Add to dashboard Cite

The characterization of an electric propulsion device cathode is performed in the so-called diode configuration with an external anode. The anode acts as a physical boundary for the cathode plasma discharge; therefore, it influences cathode operation and performances. In this study, four different anodes—namely, a disk, a plate, a long cylinder, and a short cylinder—have been used with a flat disk LaB6 emitter 5 A-class cathode to examine the anode geometry impact on cathode discharge properties. Current–voltage curves, discharge oscillations, electron parameters, and ion velocities have been measured for currents in the 2 A to 12 A range and xenon mass flow rates varied from 0.4 mg/s to 1 mg/s with a fixed cathode-to-anode distance. The set of results clearly supports the fact that the anode geometry strongly influences the cathode characteristics both at the macroscopic and the microscopic scale.

show abstract

Section: Langmuir Probe Resultsmentioning

confidence: 99%

Anode geometry influence on LaB6 cathode discharge characteristics

et al. 2019

View full text Add to dashboard Cite

show abstract

“…In our case, all particles (viewed as one species) collide together and external sources or sinks of energy create non-Maxwellian steady states. The general formula of the electron current [36,40,44,46] can be written as a function of any distribution function f (E) of the kinetic energy E of particles (35) where ψ(E) is a diffusion parameter, γ(E) a geometric parameter of the probe, U = U p − U pl is the difference between the applied potential at the probe and the plasma potential, S the surface of the probe, and m is the mass of electron. The classical regime is obtained by assuming a diffusionless limit (ψ(E) 1), and with γ = 4/3 for a spherical probes.…”

Section: B Corrections For the Langmuir Probes Interpretationsmentioning

confidence: 99%

“…Moreover, Eq. (36) (directly linked to the Druyvesteyn formula [36,40,45,46]) is the diffusionless limit of Eq. (35).…”

Section: B Corrections For the Langmuir Probes Interpretationsmentioning

confidence: 99%

“…[17,18,44] where bi-modal distribution functions (distribution function of 2 populations of particles at different temperatures) have been used. Other results are published in the literature describing effects of non-Maxwellians on the Langmuir probe measurements [36][37][38][39][40][41][42][43][44][45][46][47]. The bi-modal approximation is the first efficient way to describe NMDFs, but it assumes the superposition of two populations of particles at the Maxwellian equilibrium and the self-consistency is very restricted since in this bi-modal description the plasma is enough collisional to assure a MDF for each species but do not allow collisions between these two populations.…”

mentioning

confidence: 99%

“…(ii) Another example is the discrepancy of the Langmuir probe interpretation [36][37][38][39][40][41][42][43][44][45][46][47] with respect to the Thomson scattering measurements [48,49] of the electron temperature which has been associated with the presence of super-thermal particles [17,18] (i.e., bulk and super-thermal populations, both at different thermodynamic equilibrium). The Langmuir probe is one of the most used diagnostic for low temperature plasmas.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas

Izacard

2016

Physics of Plasmas

View full text Add to dashboard Cite

In magnetized plasma physics, almost all developed analytic theories assume a Maxwellian distribution function (MDF) and in some cases small deviations are described using the perturbation theory. The deviations with respect to the Maxwellian equilibrium, called kinetic effects, are required to be taken into account specially for fusion reactor plasmas. Generally, because the perturbation theory is not consistent with observed steady-state non-Maxwellians, these kinetic effects are numerically evaluated by very CPU-expensive codes, avoiding the analytic complexity of velocity phase space integrals. We develop here a new method based on analytic non-Maxwellian distribution functions constructed from non-orthogonal basis sets in order to (i) use as few parameters as possible, (ii) increase the efficiency to model numerical and experimental non-Maxwellians, (iii) help to understand unsolved problems such as diagnostics discrepancies from the physical interpretation of the parameters, and (iv) obtain analytic corrections due to kinetic effects given by a small number of terms and removing the numerical error of the evaluation of velocity phase space integrals. This work does not attempt to derive new physical effects even if it could be possible to discover one from the better understandings of some unsolved problems, but here we focus on the analytic prediction of kinetic corrections from analytic non-Maxwellians. As applications, examples of analytic kinetic corrections are shown for the secondary electron emission, the Langmuir probe characteristic curve, and the entropy. This is done by using three analytic representations of the distribution function: the Kappa (KDF), the bi-modal or a new interpreted non-Maxwellian (INMDF) distribution function. The existence of INMDFs is proved by new understandings of the experimental discrepancy of the measured electron temperature between two diagnostics in JET. As main results, it is shown that (i) the empirical formula for the secondary electron emission is not consistent with a MDF due to the presence of super-thermal particles, (ii) the super-thermal particles can replace a diffusion parameter in the Langmuir probe current formula and (iii) the entropy can explicitly decrease in presence of sources only for the introduced INMDF without violating the second law of thermodynamics. Moreover, the first order entropy of an infinite number of super-thermal tails stays the same as the entropy of a MDF. The latter demystifies the Maxwell's demon by statistically describing non-isolated systems.The observation of non-equilibrium distribution functions is possible in a large number of areas other than laboratory plasma physics such as in astrophysics plasmas, hydrodynamic fluids and molecular dynamics, atomic physics, condensed matter, chemical reactions and in statistics (see Refs. [1][2][3][4][5]). We focus here on laboratory plasma physics with charged particles in a magnetic field relevant to tokamaks and spherical tokamaks for the purpose of energy production by fusion ener...

show abstract

Ionization instability and turbulence in the plume of sub-ampere hollow cathodes depending on an applied magnetic field

Potrivitu

2022

CEAS Space J

View full text Add to dashboard Cite

Langmuir Probe Evaluation of the Plasma Potential in Tokamak Edge Plasma for Non‐Maxwellian EEDF

Cited by 22 publications

References 11 publications

Anode geometry influence on LaB6 cathode discharge characteristics

Anode geometry influence on LaB6 cathode discharge characteristics

Kinetic corrections from analytic non-Maxwellian distribution functions in magnetized plasmas

Ionization instability and turbulence in the plume of sub-ampere hollow cathodes depending on an applied magnetic field

Contact Info

Product

Resources

About