Neoclassical transport processes in weakly collisional plasmas with fractured velocity distribution functions

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
A. A. Kabantsev ◽  
C. F. Driscoll ◽  
D. H. E. Dubin ◽  
Yu. A. Tsidulko
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Transport Theory ◽  
Particle Energy ◽  
Distribution Functions ◽  
Transport Processes ◽  
Electrostatic Confinement ◽  
Neoclassical Transport ◽  
Novel Theory ◽  
Velocity Distribution Functions

Ripples in magnetic or electrostatic confinement fields give rise to trapping separatrices, and conventional neoclassical transport theory describes the collisional trapping/detrapping of particles with fractured distribution function. Our experiments and novel theory have now characterized a new kind of neoclassical transport processes arising from chaotic (nominally collisionless) separatrix crossings, which occur due to E × B plasma rotation along θ−ruffled or wave-perturbed separatrices. This chaotic neoclassical transport becomes dominant at low collisionality when the collisional spreading of particle energy during the dynamical period is less than the separatrix energy ruffle.

scholarly journals On the Determination of Kappa Distribution Functions from Space Plasma Observations

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 212 ◽  
Author(s):  
Georgios Nicolaou ◽  
George Livadiotis ◽  
Robert T. Wicks
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Space Plasma ◽  
Distribution Functions ◽  
Specific Method ◽  
Kappa Distribution ◽  
Kappa Index ◽  
Velocity Distribution Functions ◽  
Bulk Parameters ◽  
Plasma Bulk

The velocities of space plasma particles, often follow kappa distribution functions. The kappa index, which labels and governs these distributions, is an important parameter in understanding the plasma dynamics. Space science missions often carry plasma instruments on board which observe the plasma particles and construct their velocity distribution functions. A proper analysis of the velocity distribution functions derives the plasma bulk parameters, such as the plasma density, speed, temperature, and kappa index. Commonly, the plasma bulk density, velocity, and temperature are determined from the velocity moments of the observed distribution function. Interestingly, recent studies demonstrated the calculation of the kappa index from the speed (kinetic energy) moments of the distribution function. Such a novel calculation could be very useful in future analyses and applications. This study examines the accuracy of the specific method using synthetic plasma proton observations by a typical electrostatic analyzer. We analyze the modeled observations in order to derive the plasma bulk parameters, which we compare with the parameters we used to model the observations in the first place. Through this comparison, we quantify the systematic and statistical errors in the derived moments, and we discuss their possible sources.

Statistical Inferences of Lift-Off Velocity Distribution Function Form for Saltating Particles

2010 ◽  
Vol 108-111 ◽  
pp. 783-788
Author(s):  
Jian Jun Wu ◽  
Li Hong He
Keyword(s):  
Distribution Function ◽  
Weibull Distribution ◽  
Velocity Distribution ◽  
Goodness Of Fit ◽  
Velocity Distribution Function ◽  
Forward Direction ◽  
Distribution Functions ◽  
Velocity Distribution Functions ◽  
Lift Off ◽  
Log Normal

The lift-off velocity distribution of saltating particles, which have been proposed to characterize the dislodgement state of saltating particles, is one of the key issues in the theoretical study of windblown sand transportation. But there were various statistical relations in the early researches. In this paper, the Kolmogorov-Smirnov test for goodness-of-fit is adopted to make an inference of the most probable form of lift-off velocity distribution functions for saltating particles on the basis of the experimental data. The statistical results show that the distribution function of vertical lift-off velocities conforms better to Weibull distribution function than to the normal, log-normal, gamma and exponential ones; while, the distribution function of the absolute values of horizontal lift-off velocities is best described by log-normal distribution in forward direction and Weibull distribution in backward direction, respectively. Finally, two more examples prove to support the above conclusions.

Flowing Granular Materials and the Maxwell-Boltzmann Velocity Distribution

2000 ◽  
Author(s):  
Edward J. Boyle
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Hard Sphere ◽  
Body Force ◽  
Canonical Ensemble ◽  
Granular Flows ◽  
Velocity Distribution Function ◽  
Distribution Functions ◽  
Velocity Distribution Functions ◽  
Single Granule

Abstract The single-granule velocity distribution function is shown to be Maxwell-Boltzmann for hard-sphere granular flows at steady-state exhibiting no gradients and absent a body-force. This is accomplished by approximating the two-granule velocity distribution function as the product of two single-granule velocity distribution functions and a correlating function and by applying to a canonical ensemble a function analogous to Boltzmann’s H-function.

scholarly journals Velocity Distribution Functions and Transport Coefficients of Electron Swarms in Gases in the Presence of Crossed Electric and Magnetic Fields

1995 ◽  
Vol 48 (3) ◽  
pp. 557 ◽  
Author(s):  
KF Ness
Keyword(s):  
Distribution Function ◽  
Magnetic Fields ◽  
Velocity Distribution ◽  
Transport Coefficients ◽  
Velocity Distribution Function ◽  
Distribution Functions ◽  
Electron Motion ◽  
Electric And Magnetic Fields ◽  
Velocity Distribution Functions ◽  
Spatially Homogeneous

A multi-term solution of the Boltzmann equation is used to calculate the spatially homogeneous velocity distribution function of a dilute swarm of electrons moving through a background of denser neutral molecules in the presence of crossed electric and magnetic fields. As an example, electron motion in methane is considered.

Electromagnetic ion-cyclotron wave growth rates and their variation with velocity distribution function shape

1977 ◽  
Vol 17 (1) ◽  
pp. 123-131 ◽  
Author(s):  
Abraham Shrauner ◽  
W. C. Feldman
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Growth Rates ◽  
Velocity Distribution Function ◽  
Distribution Functions ◽  
Wave Growth ◽  
Ion Cyclotron ◽  
Velocity Distribution Functions ◽  
Velocity Moments ◽  
Function Shape

The sensitivity of electromagnetic ion-cyclotron wave growth rates to the details of the shape of proton velocity distribution functions is explored. For this purpose two different forms of bi-Lorentzian for the proton distribution functions were adopted. The growth rates for the two types of bi-Lorentzians and the biMaxwellians for the beam (hot) protons are compared. Although the growth rates for the three shapes depend on the velocity moments of the different velocity distributions in a similar way, their magnitudes were found to vary considerably.

scholarly journals The auroral O<sup>+</sup> non-Maxwellian velocity distribution function revisited

1997 ◽  
Vol 15 (2) ◽  
pp. 249-254 ◽  
Author(s):  
D. Hubert ◽  
F. Leblanc
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Velocity Distribution ◽  
Polar Angle ◽  
Velocity Distribution Function ◽  
Distribution Functions ◽  
Field Direction ◽  
Magnetic Field Direction ◽  
Velocity Distribution Functions ◽  
The Magnetic Field

Abstract. New characteristics of O+ ion velocity distribution functions in a background of atomic oxygen neutrals subjected to intense external electromagnetic forces are presented. The one dimensional (1-D) distribution function along the magnetic field displays a core-halo shape which can be accurately fitted by a two Maxwellian model. The Maxwellian shape of the 1-D distribution function around a polar angle of 21 ± 1° from the magnetic field direction is confirmed, taking into account the accuracy of the Monte Carlo simulations. For the first time, the transition of the O+ 1-D distribution function from a core halo shape along the magnetic field direction to the well-known toroidal shape at large polar angles, through the Maxwellian shape at polar angle of 21 ± 1° is properly explained from a generic functional of the velocity moments at order 2 and 4.

Subgrid modelling of ion pitch-angle scattering for magnetosheath waves in a global hybrid-Vlasov simulation

2021 ◽  
Author(s):  
Maxime Dubart ◽  
Urs Ganse ◽  
Adnane Osmane ◽  
Andreas Johlander ◽  
Markus Battarbee ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Numerical Simulations ◽  
Spatial Resolution ◽  
Pitch Angle ◽  
Space Physics ◽  
Distribution Functions ◽  
Cyclotron Instability ◽  
Angle Scattering ◽  
Velocity Distribution Functions ◽  
Proton Cyclotron

&lt;p&gt;Numerical simulations are widely used in modern space physics and are an essential tool to understand or discover new phenomena which cannot be observed using spacecraft measurements. However, numerical simulations are limited by the space grid resolution of the system and the computational costs of having a high spatial resolution. Therefore, some physics may be unresolved in part of the system due to its low spatial resolution. We have previously identified, using Vlasiator, that the proton cyclotron instability is not resolved for grid cell sizes larger than four times the inertial length in the solar wind, for waves in the downstream of the quasi-perpendicular shock in the magnetosheath of a global hybrid-Vlasov simulation. This leads to unphysically high perpendicular temperature and a dominance of the mirror mode waves. In this study, we use high-resolution simulations to measure and quantify how the proton cyclotron instability diffuses and isotropizes the velocity distribution functions. We investigate the process of pitch-angle scattering during the development of the instability and propose a method for the sub-grid modelling of the diffusion process of the instability at low resolution. This allows us to model the isotropization of the velocity distribution functions and to reduce the temperature anisotropy in the plasma while saving computational resources.&lt;/p&gt;

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