Low-Frequency Sheath Instability in a Non-Maxwellian Plasma with Energetic Ions

2004 ◽  
Vol 92 (4) ◽  
Author(s):  
Mikhail Starodubtsev ◽  
Md. Kamal-Al-Hassan ◽  
Hiroaki Ito ◽  
Noboru Yugami ◽  
Yasushi Nishida
Keyword(s):  
Low Frequency ◽  
Energetic Ions ◽  
Maxwellian Plasma

Influence of trapped energetic ions on low-frequency magnetohydrodynamic instabilities with reversed shear profile

2021 ◽  
Vol 28 (1) ◽  
pp. 012104
Author(s):  
Baofeng Gao ◽  
Huishan Cai ◽  
Feng Wang ◽  
Xiang Gao ◽  
Yuanxi Wan
Keyword(s):  
Low Frequency ◽  
Energetic Ions ◽  
Reversed Shear

Ion-cyclotron modes in weakly relativistic plasmas

1994 ◽  
Vol 51 (3) ◽  
pp. 371-379 ◽  
Author(s):  
Chandu Venugopal ◽  
P. J. Kurian ◽  
G. Renuka
Keyword(s):  
Dispersion Relation ◽  
High Frequency ◽  
Low Frequency ◽  
Dispersion Relations ◽  
The Other ◽  
Larmor Radius ◽  
Relativistic Plasmas ◽  
Ion Plasma ◽  
Maxwellian Plasma ◽  
Relativistic Dispersion

We derive a dispersion relation for the perpendicular propagation of ioncyclotron waves around the ion gyrofrequency ω+ in a weaklu relaticistic anisotropic Maxwellian plasma. These waves, with wavelength greater than the ion Larmor radius rL+ (k⊥ rL+ < 1), propagate in a plasma characterized by large ion plasma frequencies (). Using an ordering parameter ε, we separated out two dispersion relations, one of which is independent of the relativistic terms, while the other depends sensitively on them. The solutions of the former dispersion relation yield two modes: a low-frequency (LF) mode with a frequency ω < ω+ and a high-frequency (HF) mode with ω > ω+. The plasma is stable to the propagation of these modes. The latter dispersion relation yields a new LF mode in addition to the modes supported by the non-relativistic dispersion relation. The two LF modes can coalesce to make the plasma unstable. These results are also verified numerically using a standard root solver.

scholarly journals Inertial-range kinetic turbulence in pressure-anisotropic astrophysical plasmas

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
M. W. Kunz ◽  
A. A. Schekochihin ◽  
C. H. K. Chen ◽  
I. G. Abel ◽  
S. C. Cowley
Keyword(s):  
Solar Wind ◽  
Free Energy ◽  
Distribution Function ◽  
Low Frequency ◽  
Energetic Cost ◽  
Astrophysical Plasmas ◽  
Order Unity ◽  
Quantitative Measurements ◽  
Maxwellian Plasma ◽  
Field Lines

A theoretical framework for low-frequency electromagnetic (drift-)kinetic turbulence in a collisionless, multi-species plasma is presented. The result generalises reduced magnetohydrodynamics (RMHD) and kinetic RMHD (Schekochihinet al.,Astrophys. J. Suppl. Ser., vol. 182, 2009, pp. 310–377) to the case where the mean distribution function of the plasma is pressure-anisotropic and different ion species are allowed to drift with respect to each other – a situation routinely encountered in the solar wind and presumably ubiquitous in hot dilute astrophysical plasmas such as the intracluster medium. Two main objectives are achieved. First, in a non-Maxwellian plasma, the relationships between fluctuating fields (e.g. the Alfvén ratio) are order-unity modified compared to the more commonly considered Maxwellian case, and so a quantitative theory is developed to support quantitative measurements now possible in the solar wind. Beyond these order-unity corrections, the main physical feature of low-frequency plasma turbulence survives the generalisation to non-Maxwellian distributions: Alfvénic and compressive fluctuations are energetically decoupled, with the latter passively advected by the former; the Alfvénic cascade is fluid, satisfying RMHD equations (with the Alfvén speed modified by pressure anisotropy and species drifts), whereas the compressive cascade is kinetic and subject to collisionless damping (and for a bi-Maxwellian plasma splits into three independent collisionless cascades). Secondly, the organising principle of this turbulence is elucidated in the form of a conservation law for the appropriately generalised kinetic free energy. It is shown that non-Maxwellian features in the distribution function reduce the rate of phase mixing and the efficacy of magnetic stresses, and that these changes influence the partitioning of free energy amongst the various cascade channels. As the firehose or mirror instability thresholds are approached, the dynamics of the plasma are modified so as to reduce the energetic cost of bending magnetic-field lines or of compressing/rarefying them. Finally, it is shown that this theory can be derived as a long-wavelength limit of non-Maxwellian slab gyrokinetics.

Low-frequency waves and associated energetic ions downstream of Saturn

1985 ◽  
Vol 90 (A11) ◽  
pp. 10791 ◽  
Author(s):  
K. W. Behannon ◽  
M. L. Goldstein ◽  
R. P. Lepping ◽  
H. K. Wong ◽  
B. H. Mauk ◽  
...  
Keyword(s):  
Low Frequency ◽  
Energetic Ions ◽  
Low Frequency Waves

Low-frequency global Alfvén eigenmodes in low-shear tokamaks with trapped energetic ions

2009 ◽  
Vol 16 (9) ◽  
pp. 092502 ◽  
Author(s):  
V. S. Marchenko ◽  
Ya. I. Kolesnichenko ◽  
S. N. Reznik
Keyword(s):  
Low Frequency ◽  
Energetic Ions ◽  
Alfven Eigenmodes ◽  
Low Shear

Theoretical studies of low-frequency Alfvén modes in tokamak plasmas

2021 ◽  
Author(s):  
R R Ma ◽  
Liu Chen ◽  
Fulvio Zonca ◽  
Yueyan Li ◽  
Zhiyong Qiu
Keyword(s):  
Low Frequency ◽  
Acoustic Mode ◽  
Frequency Region ◽  
Physical Parameters ◽  
Linear Wave ◽  
Tokamak Plasmas ◽  
High Frequency Region ◽  
Energetic Ions ◽  
Ballooning Mode ◽  
Spectral Patterns

Abstract Linear wave properties of the low-frequency Alfvén modes (LFAMs) observed in the DIII-D tokamak experiments with reversed magnetic shear [Nucl. Fusion 61, 016029 (2021)] are theoretically studied and delineated based on the general fishbone-like dispersion relation. By adopting the representative experimental equilibrium parameters, it is found that, in the absence of energetic ions, the LFAM is a kinetic ballooning mode instability of reactive-type with a dominant Alfvénic polarization. More specifically, due to diamagnetic and trapped particle effects, the LFAM can be coupled with the beta-induced Alfvén-acoustic mode in the low-frequency region (frequency much less than the thermal-ion transit and/or bounce frequency); or with the beta-induced Alfvén eigenmode in the high frequency region (frequency higher than or comparable to the thermal-ion transit frequency); resulting in reactive-type instabilities. Moreover, the ‘Christmas light’ and ‘mountain peak’ spectral patterns of LFAMs as well as the dependence of instability drive on the electron temperature observed in the experiments can be theoretically interpreted by varying the relevant physical parameters. Conditions when dissipative-type instabilities may set in are also discussed.

NONLINEAR PLASMA OSCILLATIONS WITH TRAPPED ELECTRONS

1966 ◽  
Vol 44 (5) ◽  
pp. 1109-1119 ◽  
Author(s):  
H. S. C. Wang
Keyword(s):  
Wave Amplitude ◽  
Periodic Potential ◽  
Low Frequency ◽  
First Integral ◽  
Stationary Wave ◽  
Wave Form ◽  
Trapped Electrons ◽  
The Poisson Equation ◽  
Maxwellian Plasma ◽  
Excessive Number

Propagation of stationary longitudinal waves in a hot (Maxwellian) plasma is investigated, when the wave amplitude, phase velocity, and electron temperature are such that the relativistic effect is negligible but trapped electrons must be taken into account. The treatment is based on an exact solution of the nonlinear collisionless Boltzmann equation compatible with the equilibrium electron distribution. The existence, propagation, and amplitude limit of a dimensionless periodic potential wave ψ are discussed in terms of the behavior of the first integral Y(ψ) of the Poisson equation. It was found that, for α = mW2/2κT (W is the wave velocity) less than a critical value αe = 0.854, no stationary wave can exist, irrespective of its amplitude. For α slightly greater than αe, wave propagation is limited to small amplitude and low frequency. As α is further increased, waves of progressively larger amplitude can also propagate; but their amplitude is limited when Y(ψ) becomes tangent to the ψ axis at ψmin because of the excessive number of electrons trapped in the wave troughs. An expression for the maximum wave amplitude as a function of α is derived and plotted. Wavelengths for different values of α and amplitude levels are computed numerically and plotted as dispersion curves. A typical example for wave form is also displayed to show the progressive distortion from pure sinusoids due to nonlinearity and the effect of trapped electrons.

scholarly journals Helium in the Earth's foreshock: a global Vlasiator survey

2020 ◽  
Author(s):  
Markus Battarbee ◽  
Xóchitl Blanco-Cano ◽  
Lucile Turc ◽  
Primoz Kajdic ◽  
Vertti Tarvus ◽  
...  
Keyword(s):  
Low Frequency ◽  
Alpha Particles ◽  
Compressive Wave ◽  
Energetic Ions ◽  
Ion Distributions ◽  
Hot Plasma ◽  
Earth’S Bow Shock ◽  
Composition Analyzer ◽  
Ion Profiles ◽  
Low Frequency Waves

&lt;p&gt;The foreshock is a region of space in front of the Earth's bow shock, extending along the interplanetary magnetic field. It is permeated by ions and electrons reflected at the shock, low-frequency waves, and various plasma transients. The ion foreshock is dominated by a number of proton populations such as field-aligned beams, gyrating distributions and diffuse ions, as well as proton-excited waves. As the solar wind can contain a significant fraction of helium, it is of great interest to investigate how alpha-particles (He&lt;sup&gt;2+&lt;/sup&gt;) are reflected into forming their own foreshock. We investigate the extent of the helium foreshock in relation to foreshock ultra-low frequency waves and protons using Vlasiator, a global hybrid-Vlasov simulation. We confirm a number of historical spacecraft observations at the foreshock regions associated with field-aligned beams, gyrating ion distributions, and specularly reflected particles, performing the first numerical global survey of the helium foreshock. We present wavelet analysis at multiple positions within the foreshock and evaluate the dynamics of gyrating ion populations in response to the transverse and compressive wave components. We also present Magnetosphere Multiscale (MMS) spacecraft crossings of the foreshock edge and compare Hot Plasma Composition Analyzer (HPCA) measurements of energetic ions with our simulation data, showing the variability of the foreshock edge suprathermal ion profiles.&lt;/p&gt;

Alfvén cascade eigenmodes above the TAE-frequency and localization of Alfvén modes in D- 3 He plasmas on JET

2021 ◽  
Author(s):  
Mykola Dreval ◽  
Sergei E Sharapov ◽  
Yevgen Kazakov ◽  
Jozef Ongena ◽  
Massimo Nocente ◽  
...  
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
High Energy ◽  
Negative Ion ◽  
Energetic Ions ◽  
Fast Ions ◽  
Alfven Eigenmodes ◽  
Different Types ◽  
Central Regions ◽  
High Frequency Ac

Abstract Various types of Alfvén Eigenmodes (AEs) have been destabilized by fast ions over a broad frequency range from ~80 kHz to ~700 kHz in a series of JET experiments in mixed D-3He plasmas heated with the three-ion ICRF scenario [M. Nocente et al., Nucl. Fusion 60, 124006 (2020)]. In this paper, we identify the radial localization of AEs using an X-mode reflectometer, a multiline interferometer and soft X-ray diagnostics. The analysis is focused on the most representative example of these measurements in JET pulse #95691, where two different types of Alfvén cascade (AC) eigenmodes were observed. These modes originate from the presence of a local minimum of the safety factor qmin. In addition to ACs with frequencies below the frequency of toroidal Alfvén eigenmodes (TAEs), ACs with frequencies above the TAE frequency were destabilized by energetic ions. Both low- (f ≈80-180 kHz) and high-frequency (f ≈ 330-450 kHz) ACs were localized in the central regions of the plasma. The characteristics of the high-frequency ACs are investigated in detail numerically using HELENA, CSCAS and MISHKA codes. The resonant conditions for the mode excitation are found to be determined by passing ions of rather high energy of several hundred keV and similar to those established in JT-60U with negative-ion-based NBI [M. Takechi et al., Phys. Plasmas 12, 082509 (2005)]. The computed radial mode structure is found to be consistent with the experimental measurements. In contrast to low-frequency ACs observed most often, the frequency of the high-frequency ACs decreases with time as the value of qmin decreases. This feature is in a qualitative agreement with the analytical model of the high-frequency ACs in [B.N. Breizman et al., Phys. Plasmas 10 3649 (2003)]. The high-frequency AC could be highly relevant for future ITER and fusion reactor plasmas dominated by ~ MeV energetic ions, including a significant population of passing fast ions.

A Study on the Fine Structure of the Lateral Line Organ of the Sea Eel

1973 ◽  
Vol 31 ◽  
pp. 648-649
Author(s):  
K. Hama
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Lateral Line ◽  
Low Frequency ◽  
Sensory Cells ◽  
Apical Surface ◽  
Voltage Electron ◽  
Sensory Epithelia ◽  
Low Frequency Vibration ◽  
Transmission Electron

The lateral line organs of the sea eel consist of canal and pit organs which are different in function. The former is a low frequency vibration detector whereas the latter functions as an ion receptor as well as a mechano receptor.The fine structure of the sensory epithelia of both organs were studied by means of ordinary transmission electron microscope, high voltage electron microscope and of surface scanning electron microscope.The sensory cells of the canal organ are polarized in front-caudal direction and those of the pit organ are polarized in dorso-ventral direction. The sensory epithelia of both organs have thinner surface coats compared to the surrounding ordinary epithelial cells, which have very thick fuzzy coatings on the apical surface.

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