The L mode in electromagnetic proton-cyclotron waves in plasmas modelled by a Lorentzian distribution function

1998 ◽  
Vol 60 (1) ◽  
pp. 29-48 ◽  
Author(s):  
PEDRO VEGA ◽  
LUIS PALMA ◽  
RENE ELGUETA
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Growth Rates ◽  
Maximum Growth ◽  
High Energy ◽  
Thermal Anisotropy ◽  
Proton Concentration ◽  
Lorentzian Distribution ◽  
High Energy Tail ◽  
Proton Cyclotron

The L mode in electromagnetic proton-cyclotron waves (EPCWs) propagating parallel to a uniform ambient magnetic field is studied here analytically. A generalized Lorentzian distribution function is used to model the plasma. Analytical expressions for the wavenumber and for both the temporal and convective growth rates for a multi-ion plasma are obtained within the linear theory. This analytical approach is appropiate for β∥<1, which is the ratio of plasma kinetic pressure to magnetic field pressure. The characteristics of the unstable spectrum are found to be independent of high-energy particles. For a plasma composed of electrons plus hot and cold protons, it is shown that the maximum growth rates as functions of cold-proton concentration δ can always decrease, or can increase until δ reaches a certain peak value and decrease thereafter, or can always increase, depending on the thermal anisotropy of the hot protons. This behaviour is similar to that in Maxwellian plasmas. However, for the convective growth rate, the expression for the optimum cold-proton concentration shows a significant dependence on the spectral index κ. Therefore, when cold protons are injected, it is more difficult to obtain optimum amplification in a Lorentzian plasma than in a Maxwellian plasma. It is also shown that the influence of the high-energy tail on the generation and amplification processes of the EPCWs is controlled by thermal anisotropy and cold-ion population. As a consequence of the latter, temporal and convective growth rates can be larger than, equal to or smaller than those of Maxwellian plasmas, depending on the anisotropy of the hot-proton distribution and on the cold-proton concentration.

Resonantly unstable off-angle hydromagnetic waves

1967 ◽  
Vol 1 (1) ◽  
pp. 81-104 ◽  
Author(s):  
C. F. Kennel ◽  
H. V. Wong
Keyword(s):  
Magnetic Field ◽  
High Energy ◽  
Electrostatic Waves ◽  
High Energy Tail ◽  
Electrons And Ions ◽  
Ion Cyclotron ◽  
Cold Component ◽  
Hydromagnetic Waves ◽  
The Magnetic Field ◽  
Uniform Plasma

We consider semi-quantitatively the cyclotron resonance instability of ion cyclotron and magnetosonic waves propagating at an angle to the magnetic field in an infinite uniform plasma. The velocity distributions of electrons and ions consist of a dense cold component and a diffuse high-energy tail. If the high-energy protons are sufficiently intense and their pitch angle distributions sufficiently anisotropic, instability occurs for those waves propagating parallel to the magnetic field. If the spectrum of resonant protons is sufficiently hard, a reasonably large cone of propagating angles about the magnetic field can be unstable. Observed fluxes of trapped protons in the magnetosphere should destabilise the ion cyclotron wave at a lower intensity threshold than for at least one class of electrostatic waves.

Cyclotron instabilities of a magnetized electron plasma with anisotropic temperatures

1977 ◽  
Vol 17 (3) ◽  
pp. 453-465 ◽  
Author(s):  
C. Chiuderi ◽  
G. Einaudi ◽  
R. Giachetti
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Dispersion Relation ◽  
Growth Rates ◽  
Linear Growth ◽  
Electron Plasma ◽  
Maxwellian Distribution ◽  
Analytical Treatment ◽  
Maxwellian Distribution Function ◽  
Instability Regions

The dispersion relation for an electron plasma in a magnetic field is investigated for a bi-Maxwellian distribution function. A new set of solutions for non-perpendicular propagation is found. The linear growth rates are computed and the instability regions in the (k, cos θ) plane are determined. An approximate analytical treatment of the problem is also given for certain ranges of the parameters.

Axial and radial development of the hot electron distribution in a helicon plasma source, measured by a retarding field energy analyzer (RFEA)

2022 ◽  
Author(s):  
Lisa Buschmann ◽  
Ashild Fredriksen
Keyword(s):  
Magnetic Field ◽  
Electron Distribution ◽  
Potential Drop ◽  
Plasma Source ◽  
High Energy ◽  
Plasma Potential ◽  
Field Configuration ◽  
Field Energy ◽  
Hot Electron ◽  
High Energy Tail

Abstract The information about the electron population of a helicon source plasma that expands along a magnetic nozzle is important for understanding the plasma acceleration across the potential drop that forms in the nozzle. The electrons need an energy higher than the potential drop to escape from the source. At these energies the signal of a Langmuir probe is less accurate. An inverted RFEA measures the high-energy tail of the electrons. To reach the probe, they must have energies above the plasma potential VP, which can vary over the region of the measurement. By constructing a full distribution by applying the electron temperature Te obtained from the electron IV-curve and the VP obtained from the ion collecting RFEA or an emissive probe, a density measure of the hot electron distribution independent of VP can be obtained. The variation of the high-energy tail of the EEDF in both radial and axial directions, in the two different cases of 1) a purely expanding magnetic field nozzle, and 2) a more constricted one by applying current in a third, downstream coil was investigated. The electron densities and temperatures from the source are then compared to two analytic models of the downstream development of the electron density. The first model considers the development for a pure Boltzmann distribution while the second model takes an additional magnetic field expansion into account. A good match between the measured densities and the second model was found for both configurations. The RFEA probe also allows for directional measurement of the electron current to the probe. This property is used to compare the densities from the downstream and upstream directions, showing a much lower contribution of downstream electrons into the source for a purely expanding magnetic field in comparison to the confined magnetic field configuration.

scholarly journals Polar jet kinetics and energetics analysed from STEREO/COR data

2012 ◽  
Vol 8 (S294) ◽  
pp. 549-550 ◽  
Author(s):  
Li Feng ◽  
Weiqun Gan
Keyword(s):  
Magnetic Field ◽  
Kinetic Energy ◽  
Total Mass ◽  
Source Region ◽  
High Energy ◽  
Brightness Distribution ◽  
Particle Model ◽  
Initial Particle ◽  
High Energy Tail ◽  
The Magnetic Field

AbstractWe analyze coronagraph observations of a polar jet eruption observed by SECCHI/STEREO. The brightness distribution of the jet in white-light coronagraph images is compared with a kinetic particle model. In this first application, we consider only gravity as the dominant force on the jet particles along the magnetic field. The kinetic model explains well the observed brightness evolution. The initial particle velocity distribution is fitted by Maxwellian distributions and we find deviations of the high energy tail from the Maxwellian distributions. The jets total mass is between 3.2×1014 and 1.8×1015 g. The total kinetic energy of all the particles in the jet source region amounts from 2.1×1028 to 2.4×1029 ergs.

Particle losses due to RF-enhanced pitch-angle scattering into velocity space loss regions

1984 ◽  
Vol 32 (2) ◽  
pp. 273-281 ◽  
Author(s):  
D. Anderson ◽  
M. Lisak
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Pitch Angle ◽  
High Energy ◽  
Velocity Space ◽  
Rf Heating ◽  
Fusion Plasma ◽  
Angle Scattering ◽  
Heated Particle ◽  
Scattering Losses

The application of RF heating (ICRH or LHH) to a fusion plasma creates high-energy tails on the distribution function of the heated particle species. In the presence of loss regions in velocity space, e. g. due to particle drifts in the toroidal magnetic field ripple of a tokamak, the collisional pitch-angle scattering losses may be significantly enhanced. The present work assesses the importance of such RF-enhanced losses and explicit expressions are derived for the evolution of the loss fraction. In particular, for parameters typical of PLT we find that the loss fraction could rapidly reach high values.

Electrostatic heat flux instabilities

1978 ◽  
Vol 20 (1) ◽  
pp. 47-60 ◽  
Author(s):  
S. Peter Gary
Keyword(s):  
Heat Flux ◽  
Distribution Function ◽  
Electron Beam ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
High Energy ◽  
Electrostatic Waves ◽  
High Energy Tail ◽  
Ion Acoustic ◽  
Ion Cyclotron

The linear Vlasov dispersion relation for electrostatic waves in a homogeneous plasma is studied for instabilities driven by an electron heat flux. A two Maxwellian model of the electron distribution function gives rise to three unstable modes: the electron beam, ion-acoustic and ion cyclotron heat flux instabilities. At large Te/Ti the ion-acoustic instability has the lowest threshold; at small Te/Ti the electron beam instability is dominant; and at intermediate values of Te/Ti the ion cyclotron mode is the first to go unstable. The presence of a high energy tail on the electron distribution function raises the value of the dimensionless heat flux qe/(nemev3e) at the ion-acoustic threshold, but increasing atomic number of the ions decreases this value.

scholarly journals A Tentative Sketch for BL Lacertae Objects

1994 ◽  
Vol 159 ◽  
pp. 473-473
Author(s):  
Hélène Sol ◽  
Lourdes Vicente
Keyword(s):  
Magnetic Field ◽  
Leading Edge ◽  
Transverse Field ◽  
High Energy ◽  
Field Pattern ◽  
Kinetic Energy Density ◽  
Cross Sectional ◽  
Bl Lac Objects ◽  
High Energy Tail ◽  
Bl Lac

VLBI polarization data show magnetic field configuration parallel to the nuclear jet in quasars and perpendicular to it in BL Lac objects. It appears difficult to account for this contrast within the unified scheme for AGN. To investigate a direct explanation of this peculiarity of BL Lac objects, we study the possibilities of propagation and radiation of beams of particles in transverse ambient magnetic field. High energy streams with kinetic energy density larger than the ambient magnetic one, Ekin > Emag, can easily propagate with enhancement of the transverse magnetic field at the leading edge of the stream and reconnection of magnetic lines in its wake. Synchrotron radiation in front shocks naturally leads to the observed polarization. Moreover self-polarization, with formation of charge layers and E × B drift velocity, allows substantial propagation for even lower energy streams with Ekin < Emag, as long as their density no is large enough, typically κ = 4πnomic2/B2 > 1. Such low energy streams are non diamagnetic and do not modify the ambient field. Any high energy tail of the total particle distribution in the jet therefore radiates in the transverse field pattern. This concerns for instance the BL Lac object W Comae if we assume a proton-electron jet with bulk velocity vo = 0.1c (as the source does not require relativistic beaming so far), an equipartition magnetic field B = 0.02 G and a density of radiating particles nr = 0.05cm−3 at about 7 pc from the nucleus (knot K3). For nr/no = 10−3, one gets the stream density no = 50cm−3 which allows good propagation as κ reaches 2 × 103, and still corresponds to a moderate mass outflow of 0.06 M⊙ /year for a VLBI jet cross-sectional area of 2pc2.

Recent observations of magnetic cavities: from MHD to kinetic scale

2020 ◽  
Author(s):  
Quanqi Shi ◽  
Et al
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Distribution Function ◽  
Electron Distribution Function ◽  
Circular Cross Section ◽  
High Energy ◽  
Space Physics ◽  
Small Scale ◽  
Astrophysical Plasmas ◽  
Magnetic Bottle

&lt;p&gt;Magnetic cavities, also termed magnetic holes, dips or depression structures, have an observable magnetic field decrease in a short time span and have been widely observed in the solar wind plasmas, comet magnetospheres, terrestrial/planetary magnetosheaths, magnetospheric cusps and magnetotail plasmas since 1970s. In early observations, the structures were found in MHD scale, from tens to thousands of &amp;#961;i (proton gyroradius) with corresponding temporal scales from seconds to tens of minutes. Later, kinetic scale magnetic cavities were detected in the earth&amp;#8217;s magnetotail and magnetosheath, with size less than &amp;#961;i and sometimes close to several &amp;#961;e (electron gyroradius) and often associated with a significant electron vortex around the structure. Surprisingly, it has been found that such a small structure contains an abundance of phenomena, including different kinds of ion and electron distributions, electron or ion vortices, various types of waves, and even particle acceleration and declarations. In this presentation, we will show our recent observations of magnetic cavities from MHD scale to kinetic scale in the solar wind, magnetosheath, cusp and magnetotail. In the magnetosheath, downstream of the bow shock, the mirror mode instability can generate magnetic dip and peak trains. Using data from the new NASA satellite constellation MMS, we have found that electrons exhibit a new &amp;#8216;donut&amp;#8217; shaped distribution function related to particle deceleration processes. Using boundary normal and velocity determination techniques, we found that MHD scale magnetic cavity structures can expand or shrink, and they can enter the cusp regions along with the entry plasmas. In the turbulent magnetosheath and quiet magnetotail, we have observed kinetic scale magnetic cavity structures with scales comparable or less than one &amp;#961;i. An EMHD model and other theories will also be introduced and compared. We found that in the sheath the electron scale magnetic cavity has a circular cross section and it is a magnetic bottle in 3-D. We have also found that these structures shrink due to increases in the surrounding magnetic field, and this shrinkage of the small scale magnetic cavity can induce an electric field that accelerates the electrons to a significantly higher energy. Qualitatively distinct from other acceleration mechanisms, this process indicates a new type of non-adiabetic acceleration, and has been confirmed by the observed electron distribution function and test particle simulations. This discovery in space physics also has implications for understanding energy conversion in astrophysical plasmas, the origin of cosmic high-energy particles and plasma turbulence.&lt;/p&gt;

A comparative study of the filamentation and Weibel instabilities and their cumulative effect. I. Non-relativistic theory

2009 ◽  
Vol 75 (1) ◽  
pp. 19-33 ◽  
Author(s):  
M. LAZAR ◽  
A. SMOLYAKOV ◽  
R. SCHLICKEISER ◽  
P. K. SHUKLA
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Distribution Function ◽  
Comparative Study ◽  
Relativistic Theory ◽  
Thermal Emission ◽  
Cumulative Effect ◽  
Fusion Plasma ◽  
Thermal Anisotropy ◽  
Maxwellian Distribution Function

AbstractA comparative study of the electromagnetic instabilities in anisotropic unmagnetized plasmas is undertaken. The instabilities considered are the filamentation and Weibel instability, and their cumulative effect. Dispersion relations are derived and the growth rates are plotted systematically for the representative cases of non-relativistic counterstreaming plasmas with isotropic or anisotropic velocity distributions functions of Maxwellian type. The pure filamentation mode is attenuated by including an isotropic Maxwellian distribution function. Moreover, it is observed that counterstreaming plasmas can be fully stabilized by including bi-Maxellian distributions with a negative thermal anisotropy. This effect is relevant for fusion plasma experiments. Otherwise, for plasma streams with a positive anisotropy the filamentation and Weibel instabilities cumulate leading to a growth rate by orders of magnitude larger than that of a simple filamentation mode. This is noticeable for the quasistatic magnetic field generated in astrophysical sources, and which is expected to saturate at higher values and explain the non-thermal emission observed.

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