Plasma waves in Rosetta electric field observations in the plasma environment of comet 67P/Churyumov-Gerasimenko

2021 ◽  
Author(s):  
Elias Odelstad ◽  
Tomas Karlsson ◽  
Anders Eriksson ◽  
Fredrik Johansson
Keyword(s):  
Electric Field ◽  
Plasma Density ◽  
Plasma Waves ◽  
Lower Hybrid ◽  
Density Gradients ◽  
Cometary Plasma ◽  
Plasma Environment ◽  
Hybrid Frequency ◽  
Drift Instability ◽  
Comet 67P

<p>We perform a comprehensive statistical study of plasma wave activity observed in the electric field measurements obtained by the Langmuir probe instrument (RPC-LAP) onboard ESA's Rosetta spacecraft, which followed the comet 67P/Churyumov-Gerasimenko in its orbit around the sun for over two years in 2014-2016. We focus on waves in the range 1-30 Hz, roughly corresponding to the lower-hybrid frequency range. Here, electric field oscillations close to the local H<sub>2</sub>O<sup>+ </sup>lower hybrid frequency are common and collocated with sharp plasma density gradients, suggesting generation by the lower hybrid drift instability. We compare statistically the properties of the waves to the theoretical predictions on lower-hybrid wave generation by the lower hybrid drift instability, regarding e.g. amplitude dependence on plasma density gradients. We also examine the data for waves that can be attributed to other instabilities, such as various velocity-space anisotropies that may occur in the cometary plasma. We correlate the comet-related parameters, (relative spacecraft position, solar distance, plasma and neutral gas density, etc.) with wave-related parameters, such as amplitude/spectral density and frequency. This investigation greatly helps to clarify the importance of the plasma waves in different regions of the cometary plasma environment. </p>

Rosetta electric field observations in the plasma environment of comet 67P/Churyumov-Gerasimenko

2020 ◽  
Author(s):  
Elias Odelstad ◽  
Tomas Karlsson ◽  
Anders Eriksson
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Field Measurements ◽  
Plasma Waves ◽  
Lower Hybrid ◽  
Plasma Properties ◽  
Cometary Plasma ◽  
Plasma Environment ◽  
Hybrid Waves ◽  
Electric Field Measurements

<div>The plasma environments of active comets are dominated by the interaction of the solar wind with newly born cometary heavy ions, predominantly water group ions produced by ionization of cometary neutral volatiles over large distances in the extensive and diffuse cometary coma. The resulting vast comet-solar wind interaction region hosts a plethora of plasma instabilities, waves and turbulence phenomena, and thus constitutes a formidable natural laboratory for studying such processes.</div><div> </div><div>Waves are also important in determining many of the plasma properties of this environment. They can, e.g., heat or cool plasma populations, create supra-thermal electrons responsible for X-ray emissions, reduce plasma anisotropies and gradients, couple different plasma species, and provide anomalous resistivity.</div><div> </div><div>Electric field measurements in the cometary plasma environment have until recently been rare, and have only been performed during short fly-by missions, at relatively large distances from the comet nucleus. The electric field measurements by the LAP instrument onboard the Rosetta spacecraft, collected during more than two years in the vicinity of comet 67P/Churyumov-Gerasimenko therefore represent a truly unique data set.</div><div> </div><div>We use the database of 60 Hz electric field measurements of waves in the lower-hybrid frequency range, and correlate the comet-related parameters, (relative spacecraft position, solar distance, plasma and neutral gas density, etc.) with wave related parameters, such as amplitude/spectral density and frequency. We also compare statistically the properties of the waves with theoretical predictions of lower-hybrid wave generation, regarding e.g. amplitude dependence on plasma density gradients, with the aim of clarifying the importance of the plasma waves in different regions of the cometary plasma environment.</div><div> </div><div>Electric field measurements allow investigating both electrostatic wave modes and electromagnetic ones. We investigate frequencies and amplitudes of the electric field oscillations and use background magnetic field values and plasma properties to determine relevant expected frequencies, as well as magnetic field oscillations (for low and medium frequencies) to determine if the plasma waves are electrostatic or electromagnetic. Lower hybrid waves are almost electrostatic, but have a small magnetic field signature from second order effects. Determination of the most common wave modes gives an indication of the role of plasma waves in the cometary plasma environment probed by Rosetta.</div><div> </div><div>Lower hybrid waves are common in the inner coma of 67P. Such waves are predicted to energize electrons parallel to the ambient magnetic field, and ions in the perpendicular direction. With the help of ion and electron data, we test this prediction, which may explain the presence of a hot electron population reported on, but of hitherto unknown origin. These results give clues to the role of the waves in the formation of the cometary plasma environment.</div>

scholarly journals TEMPORAL EVOLUTION OF THE LOWER HYBRID CAVITIES IN THE IONOSPHERE PLASMA DUE TO TURBULENT DIFFUSION

2019 ◽  
pp. 27-30
Author(s):  
N.A. Azarenkov ◽  
D.V. Chibisov ◽  
N.I. Kovalenko ◽  
D.I. Maslennikov
Keyword(s):  
Plasma Density ◽  
Turbulent Diffusion ◽  
Inhomogeneous Plasma ◽  
Radial Dependence ◽  
Lower Hybrid ◽  
Ionosphere Plasma ◽  
Plasma Density Distribution ◽  
Initial Plasma ◽  
Drift Instability ◽  
Radially Inhomogeneous

The problem of evolution and disappearance of the lower hybrid cavities that are observed in the plasma of the Earth’s ionosphere is solved. It is assumed that the destruction of the cavity is caused by turbulent diffusion of plasma, which arises due to the drift instability of radially inhomogeneous plasma. The initial plasma density distribution on the radius in the cavity is considered to be the inverse Gaussian distribution. A solution of the diffusion equation is obtained, which at any time determines the radial dependence of the plasma density in the cavity. In the asymptotic limit t →∞ the plasma density in the cavity becomes equal to the density of the surrounding plasma.

Investigation of the plasma-wave interaction in helicon plasmas near the lower hybrid frequency

2021 ◽  
Author(s):  
Yide Zhao ◽  
Jinwei Bai ◽  
Yong Cao ◽  
Siyu Wu ◽  
Bin Tian
Keyword(s):  
Plasma Wave ◽  
Plasma Density ◽  
Interaction Model ◽  
Local Maximum ◽  
Wave Interaction ◽  
Lower Hybrid ◽  
Maximum Plasma ◽  
Power Deposition ◽  
Hybrid Frequency ◽  
Plasma Resistance

Abstract The study of the characteristics of the plasma-wave interaction in helicon plasmas near the lower hybrid frequency has been carried out. The (0D) dispersion relation is derived to analyse the properties of the wave propagation and the 1D cylindrical plasma-wave interaction model is established to investigate the power deposition and implement the parametric analysis. It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates a very thin layer near the boundary. Therefore, it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks. It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.

Radiation of electrostatic plasma waves near the lower hybrid frequency

1977 ◽  
Vol 16 (1) ◽  
pp. 387-393 ◽  
Author(s):  
Toshiro Ohnuma ◽  
Kan Shibata ◽  
Saburo Adachi
Keyword(s):  
Plasma Waves ◽  
Lower Hybrid ◽  
Hybrid Frequency ◽  
Electrostatic Plasma Waves

Possible beneficial ponderomotive force effects on fast-wave coupling in tokamaks

1994 ◽  
Vol 51 (3) ◽  
pp. 433-440 ◽  
Author(s):  
V. A. Petržílka
Keyword(s):  
Reflection Coefficient ◽  
Electric Field ◽  
Density Gradient ◽  
Plasma Density ◽  
Ponderomotive Force ◽  
Local Electric Field ◽  
Lower Hybrid ◽  
Fast Wave ◽  
Ponderomotive Forces ◽  
Boundary Plasma

At lower-hybrid frequencies in tokamaks, ponderomotive forces at fast-wave launching typically lead in the vicinity of the launching structure to a boundary plasma density increase. This results in a decrease in the reflection coefficient, and, in detached plasmas, to the appearance of a local electric field maximum at several centimetres from the launching grill structure; this electric field maximum is connected to the reversal of the plasma density gradient near the grill mouth because of ponderomotive force effects.

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