scholarly journals Ion temperature anisotropy across a magnetotail reconnection jet

2015 ◽  
Vol 42 (18) ◽  
pp. 7239-7247 ◽  
Author(s):  
H. Hietala ◽  
J. F. Drake ◽  
T. D. Phan ◽  
J. P. Eastwood ◽  
J. P. McFadden
Keyword(s):  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Magnetotail Reconnection

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.

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>

Wave scattering processes in a plasma with ion temperature anisotropy

1991 ◽  
Vol 44 (6) ◽  
pp. 599-602 ◽  
Author(s):  
H Wilhelmsson ◽  
V N Pavlenko ◽  
V G Panchenko
Keyword(s):  
Wave Scattering ◽  
Ion Temperature ◽  
Temperature Anisotropy

Comparison of different techniques to estimate the direction of the Poynting vector of EMIC emissions

2021 ◽  
Author(s):  
Benjamin Grison ◽  
Ondrej Santolik
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Poynting Vector ◽  
Source Region ◽  
Transverse Component ◽  
Equatorial Region ◽  
Magnetic Equator ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Single Plane

<p>Electromagnetic Ion Cyclotron (EMIC) waves usually grow in the inner magnetosphere from hot ion temperature anisotropy. The main source region is located close to the magnetic equator and there is a secondary EMIC source region off the magnetic equator in the dayside magnetosphere. The source region can be identified using measurements of the Poynting vector direction.</p><p>The Poynting vector is ideally derived from the measurement of 3 components of the wave electric field and 3 components of components of the wave magnetic field. However, spinning spacecraft often have only two long mutually perpendicular electric antennas in the spin plane, deployed by the centrifugal force. The third antenna, when present, is usually shorter owing to difficulties of deploying a antenna along the spin axis.</p><p>Estimations of the Poynting vector from measurements of three magnetic field components and two electric field components can be obtained assuming the presence of a single plane wave (and thus perpendicularity of the electric field and the magnetic field vectors, according to the Faraday’s law), following the method developed by Loto'aniu et al. (2005). Applying this method to Cluster data, Allen et al. (2013) found the presence of bidirectional EMIC emissions off the magnetic equatorial region.</p><p>Another technique proposed earlier by Santolík et al. (2001) considers the phase shift estimation between the electric signals from each antenna and synthetic perpendicular magnetic field components obtained from the three-dimensional measurements. The method is based on cross-spectral estimates in the frequency domain and can be used to estimate sign of each component of the Poynting vector. Using this technique Grison et al. (2016) showed the importance of the transverse component of the EMIC emissions far from the source region.</p><p>We compare these methods for different events to check how the results of these two techniques differ. We also discuss what we can learn about the EMIC source region from these measurements.</p>

Statistical occurrence of mirror mode waves at Mars

2020 ◽  
Author(s):  
Cyril Simon Wedlund ◽  
Martin Volwerk ◽  
Christian Mazelle ◽  
Christian Möstl ◽  
Diana Rojas-Castillo ◽  
...  
Keyword(s):  
Solar Cycle ◽  
High Plasma ◽  
Bow Shock ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Frequency Wave ◽  
Solar Cycle 24 ◽  
Mirror Mode ◽  
Cycle 24 ◽  
Mm Waves

<p>Ultra low-frequency wave activity such as mirror mode (MM) waves, arising from an ion temperature anisotropy in the plasma, has been ubiquitously detected in the magnetosheaths of Venus and Mars. The MM instability is usually triggered behind a quasi-perpendicular bow shock in a high plasma β. We present here a statistical survey of these waves at Mars using magnetometer and ion data from the NASA/MAVEN mission between 2014 and 2019 (solar cycle 24, receding activity). First, quasi-perpendicular bow shock crossings are identified in the data using simple bow shock models (Edberg et al. 2008, Gruesbeck et al. 2018, Hall et al. 2019). MM waves are then automatically detected for these conditions, first from magnetometer measurements only (in the manner of Volwerk et al., 2016), and second using both magnetometer and ion moments to refine the analysis. Maps of MM wave occurrence for solar cycle 24 are presented and preliminary comparisons with similar and different solar activity conditions with MGS and Mars Express data are discussed.</p>

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