Ion temperature anisotropy in the auroral F-region as measured with EISCAT

1986 ◽  
Vol 48 (9-10) ◽  
pp. 959-971 ◽  
Author(s):  
U.P Løvhaug ◽  
T Flå
Keyword(s):  
Ion Temperature ◽  
Temperature Anisotropy ◽  
F Region

Ion temperature anisotropy effects on the dispersion relation and threshold conditions of a sheared current-driven electrostatic ion-acoustic instability with applications to the collisional high-latitude F-region

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
Patrick J.G. Perron ◽  
J.-M. Noël ◽  
J.-P. St-Maurice ◽  
K. Kabin
Keyword(s):  
Dispersion Relation ◽  
Wave Vector ◽  
High Latitude ◽  
Instability Threshold ◽  
Larmor Radius ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
F Region ◽  
Threshold Conditions ◽  
Ion Acoustic

Plasma instabilities play a important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. Ion temperature anisotropies with enhanced perpendicular temperature often exist in the high-latitude F-region. In addition to temperature anisotropies, ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). We investigated whether ion temperature anisotropy lowers the threshold conditions required for the onset of sheared CDEIA instabilities. We generalised a dispersion relation to include ion thermal anisotropy, finite Larmor radius corrections and collisions. We derived new fluid-like analytical expressions for the threshold conditions required for instability that depend explicitly on ion temperature anisotropy. We studied how the instability threshold conditions vary as a function of the wave vector direction in both fluid and kinetic regimes. We found that, despite the dampening effect of collisions on ion-acoustic waves, ion temperature anisotropy lowers in some cases the threshold drift requirements for a large range of oblique wave vector angles. More importantly, realistic ion temperature anisotropies contribute to reducing the instability threshold velocity shears that are associated with small drift thresholds, for modes propagating almost perpendicularly to the geomagnetic field. Small shear thresholds that seem to be sustainable in the ionospheric F-region are obtained for low-frequency waves. Such instabilities could play a role in the direct generation of field-aligned irregularities in the collisional F-region that could be observed with the Super Dual Auroral Radar Network (SuperDARN) array of high-frequency radars. These modes would be very sensitive to the radar probing direction since they are restricted to very narrow angular intervals. The ion temperature anisotropy is an important parameter that needs to be considered in the studies of sheared and collisional CDEIA waves and instabilities in the high-latitude F-region.

scholarly journals Ion temperature anisotropy effects on threshold conditions of a shear-modified current driven electrostatic ion-acoustic instability in the topside auroral ionosphere

2013 ◽  
Vol 31 (3) ◽  
pp. 451-457 ◽  
Author(s):  
P. J. G. Perron ◽  
J.-M. A. Noël ◽  
K. Kabin ◽  
J.-P. St-Maurice
Keyword(s):  
Acoustic Waves ◽  
Larmor Radius ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Finite Larmor Radius ◽  
Acoustic Instability ◽  
Preferred Direction ◽  
F Region ◽  
Threshold Conditions ◽  
Ion Acoustic

Abstract. Temperature anisotropies may be encountered in space plasmas when there is a preferred direction, for instance, a strong magnetic or electric field. In this paper, we study how ion temperature anisotropy can affect the threshold conditions of a shear-modified current driven electrostatic ion-acoustic (CDEIA) instability. In particular, this communication focuses on instabilities in the context of topside auroral F-region situations and in the limit where finite Larmor radius corrections are small. We derived a new fluid-like expression for the critical drift which depends explicitly on ion anisotropy. More importantly, for ion to electron temperature ratios typical of F-region, solutions of the kinetic dispersion relation show that ion temperature anisotropy may significantly lower the drift threshold required for instability. In some cases, a perpendicular to parallel ion temperature ratio of 2 and may reduce the relative drift required for the onset of instability by a factor of approximately 30, assuming the ion-acoustic speed of the medium remains constant. Therefore, the ion temperature anisotropy should be considered in future studies of ion-acoustic waves and instabilities in the high-latitude ionospheric F-region.

The BEAN experiment - An EISCAT study of ion temperature anisotropies

1995 ◽  
Vol 13 (2) ◽  
pp. 177-188 ◽  
Author(s):  
I. W. McCrea ◽  
G. O. L. Jones ◽  
M. Lester
Keyword(s):  
Velocity Distribution ◽  
Frictional Heating ◽  
Molecular Ions ◽  
Line Of Sight ◽  
Thermal Velocity ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Ion Heating ◽  
Aspect Angle ◽  
F Region

Abstract. Results are presented from a novel EISCAT special programme, SP-UK-BEAN, intended for the direct measurement of the ion temperature anisotropy during ion frictional heating events in the high-latitude F-region. The experiment employs a geometry which provides three simultaneous estimates of the ion temperature in a single F-region observing volume at a range of aspect angles from 0° to 36°. In contrast to most previous EISCAT experiments to study ion temperature anisotropies, field-aligned observations are made using the Sodankylä radar, while the Kiruna radar measures at an aspect angle of the order of 30°. Anisotropic effects can thus be studied within a small common volume whose size and altitude range is limited by the radar beamwidth, rather than in volumes which overlap but cover different altitudes. The derivation of line-of-sight ion temperature is made more complex by the presence of an unknown percentage of atomic and molecular ions at the observing altitude and the possibility of non-Maxwellian distortion of the ion thermal velocity distribution. The first problem has been partly accounted for by insisting that a constant value of electron temperature be maintained. This enables an estimate of the ion composition to be made, and facilitates the derivation of more realistic line-of-sight ion temperatures and temperature anisotropies. The latter problem has been addressed by assuming that the thermal velocity distribution remains bi-Maxwellian. The limitations of these approaches are discussed. The ion temperature anisotropies and temperature partition coefficients during two ion heating events give values intermediate between those expected for atomic and for molecular species. This result is consistent with an analysis which indicates that significant proportions of molecular ions (up to 50%) were present at the times of greatest heating.

The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA)

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
E. E. Scime ◽  
P. A. Keiter ◽  
M. M. Balkey ◽  
J. L. Kline ◽  
X. Sun ◽  
...  
Keyword(s):  
Double Layer ◽  
Noble Gas ◽  
Velocity Distribution Function ◽  
Plasma Source ◽  
Distribution Functions ◽  
Double Layers ◽  
Driving Frequency ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Ion Distribution

The West Virginia University Hot hELIcon eXperiment (HELIX) provides variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments in the Large Experiment on Instabilities and Anisotropy (LEIA) as well as fundamental studies of helicon source physics in HELIX. Through auxiliary ion heating, the ion temperature anisotropy (T⊥/T∥) is variable from 1 to 20 for parallel plasma beta (β = 8πnkTi∥/B2) values that span the range of 0.0001 to 0.01 in LEIA. The ion velocity distribution function is measured throughout the discharge volume in steady-state and pulsed plasmas with laser induced fluorescence (LIF). The wavelengths of very short wavelength electrostatic fluctuations are measured with a coherent microwave scattering system. Operating at low neutral pressures triggers spontaneous formation of a current-free electric double layer. Ion acceleration through the double layer is detected through LIF. LIF-based velocity space tomography of the accelerated beam provides a two-dimensional mapping of the bulk and beam ion distribution functions. The driving frequency for the m = 1 helical antenna is continuously variable from 8.5 to 16 MHz and frequency dependent variations of the RF coupling to the plasma allow the spontaneously appearing double layers to be turned on and off without modifying the plasma collisionality or magnetic field geometry. Single and multi-species plasmas are created with argon, helium, nitrogen, krypton, and xenon. The noble gas plasmas have steep neutral density gradients, with ionization levels reaching 100% in the core of the plasma source. The large plasma density in the source enables the study of Aflvén waves in the HELIX device.

Anomalous transport driven by ion temperature gradient instability in an anisotropic deuterium-tritium plasma

2021 ◽  
Author(s):  
Debing Zhang ◽  
Limin Yu ◽  
Erbing Xue ◽  
Xianmei Zhang ◽  
Haijun Ren
Keyword(s):  
Temperature Gradient ◽  
Anomalous Transport ◽  
Equilibrium Distribution Function ◽  
Base Case ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Ion Temperature Gradient ◽  
Anisotropic Factor ◽  
Factor Alpha ◽  
Gradient Instability

Abstract In the nowadays and future fusion devices such as ITER and CFETR, as the use of various heating schemes, the parallel and perpendicular temperature of plasmas can be different; this temperature anisotropy may have significant effects on the turbulence. In this work, the anomalous transport driven by the ion temperature gradient instability is investigated in an anisotropic deuterium-tritium (D-T) plasma. The anisotropic factor $\alpha$, defined as the ratio of perpendicular temperature to parallel temperature, is introduced to describe the temperature anisotropy in the equilibrium distribution function of D. The linear dispersion relation in local kinetic limit is derived, and then numerically evaluated to study the dependence of mode frequency on the anisotropic factor $\alpha$ and the proportion for T particle $\vareT$ by choosing three sets of typical parameters, denoted as the cyclone base case (CBC), ITER and CFETR cases. Based on the linear results, the mixing length model approximation is adopted to analyze the quasi-linear particle and energy fluxes for D and T. It is found that choosing small $\alpha$ and large $\vareT$ is beneficial for the confinement of particle and energy for D and T. This work may be helpful for the estimation of turbulent transport level in the ITER and CFETR devices.

scholarly journals Velocity shear and current driven instability in a collisional F-region

2009 ◽  
Vol 27 (1) ◽  
pp. 381-394 ◽  
Author(s):  
P. J. G. Perron ◽  
J.-M. A. Noël ◽  
J.-P. St.-Maurice
Keyword(s):  
Dispersion Relation ◽  
Electron Temperature ◽  
Current Density ◽  
Threshold Current ◽  
Velocity Shear ◽  
Ion Temperature ◽  
Fluid Limit ◽  
Low Frequencies ◽  
F Region ◽  
Threshold Conditions

Abstract. We have studied how the presence of collisions affects the behavior of instabilities triggered by a combination of shears and parallel currents in the ionosphere under a variety of ion to electron temperature ratios. To this goal we have numerically solved a kinetic dispersion relation, using a relaxation model to describe the effects of ion and electron collisions. We have compared our solutions to expressions derived in a fluid limit which applied only to large electron to ion temperature ratios. We have limited our study to threshold conditions for the current density and the shears. We have studied how the threshold varies as a function of the wave-vector angle direction and as a function of frequency. As expected, we have found that for low frequencies and/or elevated ion to electron temperature ratios, the kinetic dispersion relation has to be used to evaluate the threshold conditions. We have also found that ion velocity shears can significantly lower the field-aligned threshold current needed to trigger the instability, especially for wave-vectors close to the perpendicular to the magnetic field. However the current density and shear requirements remain significantly higher than if collisions are neglected. Therefore, for ionospheric F-region applications, the effect of collisions should be included in the calculation of instabilities associated with horizontal shears in the vertical flow. Furthermore, in many situations of interest the kinetic solutions should be used instead of the fluid limit, in spite of the fact that the latter can be shown to produce qualitatively valid solutions.

Study of mirror effect on scrape-off layer-divertor plasma based on a generalized fluid model incorporating ion temperature anisotropy

2018 ◽  
Vol 58 (6-8) ◽  
pp. 556-562 ◽  
Author(s):  
S. Togo ◽  
T. Takizuka ◽  
D. Reiser ◽  
K. Hoshino ◽  
K. Ibano ◽  
...  
Keyword(s):  
Fluid Model ◽  
Mirror Effect ◽  
Ion Temperature ◽  
Temperature Anisotropy

Free energy sources in kinetic scale current sheets formed in collisionless plasma turbulence

2020 ◽  
Author(s):  
Neeraj Jain ◽  
Joerg Buechner
Keyword(s):  
Solar Wind ◽  
Free Energy ◽  
Collisionless Plasma ◽  
Plasma Turbulence ◽  
Energy Sources ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Current Sheets ◽  
Adiabatic Cooling ◽  
Collisionless Dissipation

<p>Spacecraft observations show the radial dependence of the solar wind temperature to be slower than what is expected from the adiabatic cooling of the solar wind expanding radially outwards from the sun. The most viable process considered to explain the observed slower-than-adiabatic cooling is the heating of the solar wind plasma by dissipation of the turbulent fluctuations. In solar wind which is  a collisionless plasma in turbulent state, macroscopic energy is cascaded down to kinetic scales where kinetic plasma processes can finally dissipate the energy into heat. The kinetic scale plasma processes responsible  for the dissipation of energy are, however, not well understood. A number of observational and simulation studies have shown that the heating is concentrated in and around current sheets self-consistently formed at kinetic scales. The current sheets contain free energy sources for the growth of plasma instabilities which can serve as the mechanism of the collisionless dissipation. A detailed information on the free energy sources contained in these current sheets of plasma turbulence is lacking but essential to understand the role of  plasma instabilities in collisionless dissipation.</p><p>We carry out 2-D hybrid simulations of kinetic plasma turbulence to study in detail free energy sources available in the current sheets formed in the turbulence. We focus on three free energy sources, namely, plasma density gradient, velocity gradients for both ions and electrons and ion temperature anisotropy. Our simulations show formation of current sheets in which electric current parallel to the externally applied magnetic field flows in a thickness of the order of an ion inertial length. Inside a current sheet, electron flow velocity dominates ion flow velocity in the parallel direction resulting in a larger cross-gradient of the former. The perpendicular electron velocity inside a current sheet also has variations sharper than the corresponding ion velocity. Cross gradients in plasma density are weak (under 10 % variation inside current sheets). Ion temperature is anisotropic in current sheets. Thus the current in the sheets is primarily due to electron shear flow. A theoretical model to explain the difference between electron and ion velocities in current sheets is developed. Spacecraft observations of electron shear flow in space plasma turbulence will be pointed out.   </p><p>These results suggest that the current sheets formed in kinetic plasma turbulence are close to the force free equilibrium rather than the often assumed Harris equilibrium.  This demands investigations of the linear stability properties and nonlinear evolution of force free current sheets with temperature anisotropy. Such studies can provide effective dissipation coefficients to be included in macroscopic model of the solar wind evolution.   </p>

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