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.

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.

New kinetic cyclotron instability for electron beam in time-changing magnetic fields

2020 ◽  
Vol 86 (3) ◽  
Author(s):  
Irena Vorgul ◽  
M. Ayling ◽  
C. R. Straub ◽  
D. M. MacKay ◽  
J. D. Houghton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Velocity Distribution ◽  
Cyclotron Resonance ◽  
Cyclotron Frequency ◽  
Resonance Condition ◽  
Velocity Distribution Function ◽  
Spatial Gradient ◽  
Total Change ◽  
The Magnetic Field

This paper examines the velocity distribution function and cyclotron resonance conditions for a beam of electrons moving in a magnetic field which gradually changes with time. A spatial gradient of magnetic field is known to result in an unstable horseshoe distribution of electrons. The field gradient in time adds additional effects due to an induced electric field. The resultant anisotropic velocity distribution function, which we call a Luvdisk distribution, has some distinctive properties when compared to the horseshoe. Fitting the cyclotron resonance condition circle shows that the frequency of the resultant emission is under the local cyclotron frequency. While the spatial gradient results in the emission coming almost perpendicularly to the field, the direction of the radiation under a time-changing field has more variability. The Luvdisk distribution also arises when the magnetic field has a gradient both in space and time. The beam can be unstable if those gradients are added or subtracted from each other (if the gradients are of equal or different sign), which occurs even when the total change of magnetic field is negative. While the frequency of the emission is related to the final magnetic field value, its direction is indicative of the field’s history which produced the instability.

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.

A 3 T superconducting magnet for long-run magnetic Compton-scattering experiments

1998 ◽  
Vol 5 (3) ◽  
pp. 937-939 ◽  
Author(s):  
Nobuhiko Sakai ◽  
Hiroshi Ohkubo ◽  
Yasushi Nakamura
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Compton Scattering ◽  
Superconducting Magnet ◽  
Field Direction ◽  
Compton Profile ◽  
Magnetic Field Direction ◽  
Long Run ◽  
Radiation Shields ◽  
The Magnetic Field

A 3 T superconducting magnet has been designed and constructed for magnetic Compton-profile (MCP) measurements with the new capabilities that the magnetic field direction can be altered quickly (within 5 s) and liquid-He refill is not required for more than one week. For the latter capability, two refrigerators have been directly attached to the cryostat to maintain the low temperature of the radiation shields and for the recondensation of liquid He. The system has been satisfactorily operated for over one week.

scholarly journals Observations of diffusion in the electron halo and strahl

2016 ◽  
Vol 34 (12) ◽  
pp. 1175-1189 ◽  
Author(s):  
Chris Gurgiolo ◽  
Melvyn L. Goldstein
Keyword(s):  
Magnetic Field ◽  
Energy Range ◽  
Lower Energy ◽  
Three Dimensional ◽  
Distribution Functions ◽  
Electron Velocity ◽  
Electron Velocity Distribution ◽  
Velocity Distribution Functions ◽  
The Magnetic Field ◽  
Solar Wind Electron

Abstract. Observations of the three-dimensional solar wind electron velocity distribution functions (VDF) using ϕ–θ plots often show a tongue of electrons that begins at the strahl and stretches toward a new population of electrons, termed the proto-halo, that exists near the projection of the magnetic field opposite that associated with the strahl. The energy range in which the tongue and proto-halo are observed forms a “diffusion zone”. The tongue first appears in energy generally near the lower-energy range of the strahl and in the absence of any clear core/halo signature. While the ϕ–θ plots give the appearance that the tongue and proto-halo are derived from the strahl, a close examination of their density suggests that their source is probably the upper-energy core/halo electrons which have been scattered by one or more processes into these populations.

scholarly journals Mid-infrared Observations of Magnetic Fields in the Disks of Bi-Polar Outflow Sources

1997 ◽  
Vol 163 ◽  
pp. 799-800
Author(s):  
Craig H. Smith ◽  
Christopher M. Wright ◽  
David K. Aitken ◽  
Patrick F. Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Configuration ◽  
Field Direction ◽  
Magnetic Field Direction ◽  
Poloidal Field ◽  
Mid Infrared ◽  
Infrared Observations ◽  
Polarization Mechanism ◽  
The Magnetic Field

AbstractWe present the results from mid-infrared spectro-polarimetric observations of a number of bi-polar outflow sources. The specto-polarimetric data provides information on the polarization mechanism and the magnetic field direction. The field direction in the disks of the observed sources is most often normal to the ambient field direction and lies in the plane of the disk, indicating a toroidal rather than poloidal field configuration.

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