Impact of velocity space distribution on hybrid kinetic-magnetohydrodynamic simulation of the (1,1) mode

2008 ◽  
Vol 15 (7) ◽  
pp. 072507 ◽  
Author(s):  
Charlson C. Kim ◽  
Keyword(s):  
Velocity Space ◽  
Space Distribution ◽  
Magnetohydrodynamic Simulation

scholarly journals A universal mirror wave-mode threshold condition for non-thermal space plasma environments

2002 ◽  
Vol 9 (2) ◽  
pp. 75-78 ◽  
Author(s):  
M. P. Leubner ◽  
N. Schupfer
Keyword(s):  
Wave Mode ◽  
Instability Threshold ◽  
Velocity Space ◽  
Space Distribution ◽  
Instability Criterion ◽  
Threshold Condition ◽  
Magnetic Fluctuations ◽  
Plasma Parameters ◽  
Energy Principle ◽  
Loss Cone

Abstract. Magnetic fluctuations are recognized in a large variety of space plasmas by increasingly high resolution, in situ observations as mirror wave mode structures. A typical requirement for the excitation of mirror modes is a dominant perpendicular pressure in a high-beta plasma environment. Contrary, we demonstrate from a realistic kinetic analysis how details of the velocity space distributions are of considerable significance for the instability threshold. Introducing the most common characteristics of observed ion and electron distributions by a mixed suprathermal-loss-cone, we derive a universal mirror instability criterion from an energy principle for collisionless plasmas. As a result, the transition from two temperature Maxwellians to realistic non-thermal features provides a strong source for the generation of mirror wave mode activity, reducing drastically the instability threshold. In particular, a number of space-related examples illuminate how the specific structure of the velocity space distribution dominates as a regulating excitation mechanism over the effects related to changes in the plasma parameters.

scholarly journals Wave Induced Synergetic Electron Acceleration in Inhomogeneous Solar Plasmas

2001 ◽  
Vol 203 ◽  
pp. 544-546 ◽  
Author(s):  
M. P. Leubner
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Ad Hoc ◽  
Uniform Space ◽  
Velocity Space ◽  
Space Distribution ◽  
Alfven Wave ◽  
Magnetic Field Profile ◽  
Multi Stage ◽  
Solar Plasmas

Suprathermal electron populations are generated efficiently in uniform space plasmas by resonant Landau interaction with broadband Alfvén wave spectra. Based on a simulation of the particle acceleration in response to the wave energy input within the Fokker-Planck formalism, details of the time evolution of the velocity space distribution towards commonly observed solar wind power law spectra are discussed. Furthermore, it is shown that the diffusion properties and consequently the particle energization change significantly in astrophysical environments with magnetic field and density gradients, since synergetic effects become dominant. Electrons are accelerated resonantly out of the bulk of the distribution such that they interact again with a wave packet of higher phase velocity, leading to a multi-stage energization. Hence, a unique acceleration mechanism can be achieved without postulating pre-acceleration by ad hoc mechanisms. Depending on the density and magnetic field profile, significant enhancement of energetic particles as well as stagnation in a saturated stage of suprathermal, non-Maxwellian velocity space distributions is possible. The importance of synergetic acceleration in complex solar flare structures and for solar wind heating mechanisms is discussed in relation to spacecraft observations.

scholarly journals Signatures of the resonances of a large Galactic bar in local velocity space

2019 ◽  
Vol 626 ◽  
pp. A41 ◽  
Author(s):  
G. Monari ◽  
B. Famaey ◽  
A. Siebert ◽  
C. Wegg ◽  
O. Gerhard
Keyword(s):  
Distribution Function ◽  
Angular Momentum ◽  
Velocity Structure ◽  
Realistic Model ◽  
Velocity Space ◽  
Action Space ◽  
Space Distribution ◽  
Local Velocity ◽  
Phase Mixing ◽  
Spiral Arms

The second data release of the Gaia mission has revealed a very rich structure in local velocity space. In terms of in-plane motions, this rich structure is also seen as multiple ridges in the actions of the axisymmetric background potential of the Galaxy. These ridges are probably related to a combination of effects from ongoing phase-mixing and resonances from the spiral arms and the bar. We have recently developed a method for capturing the behaviour of the stellar phase-space distribution function at a resonance by re-expressing it in terms of a new set of canonical actions and angles variables valid in the resonant region. Here, by properly treating the distribution function at resonances, and by using a realistic model for a slowly rotating large Galactic bar with pattern speed Ωb = 39 km s−1 kpc−1, we show that no fewer than six ridges in local action space can be related to resonances with the bar. Two of these ridges at low angular momentum correspond to the corotation resonance, and can be associated with the Hercules moving group in local velocity space. Another ridge at high angular momentum corresponds to the outer Lindblad resonance, and can tentatively be associated with the velocity structure seen as an arch at high azimuthal velocities in Gaia data. The other ridges are associated with the 3:1, 4:1, and 6:1 resonances. The last can be associated with the so-called “horn” of the local velocity distribution. While it is clear that effects from spiral arms and incomplete phase-mixing related to external perturbations also play a role in shaping the complex kinematics revealed by Gaia data, the present work demonstrates that, contrary to common misconceptions, the bar alone can create multiple prominent ridges in velocity and action space.

Orbit Tomography of energetic particle distribution functions

2021 ◽  
Author(s):  
Luke Stagner ◽  
William W Heidbrink ◽  
Mirko Salewski ◽  
Asger Schou Jacobsen ◽  
Benedikt Geiger
Keyword(s):  
Distribution Function ◽  
Phase Space ◽  
Energetic Particle ◽  
Particle Distribution ◽  
Distribution Functions ◽  
Velocity Space ◽  
Space Distribution ◽  
Weight Functions ◽  
Ion Distribution ◽  
Fast Ions

Abstract Both fast ions and runaway electrons are described by distribution functions, the understanding of which are of critical importance for the success of future fusion devices such as ITER. Typically, energetic particle diagnostics are only sensitive to a limited subsection of the energetic particle phase-space which is often insufficient for model validation. However, previous publications show that multiple measurements of a single spatially localized volume can be used to reconstruct a distribution function of the energetic particle velocity-space by using the diagnostics' velocity-space weight functions, i.e. Velocity-space Tomography. In this work we use the recently formulated orbit weight functions to remove the restriction of spatially localized measurements and present Orbit Tomography, which is used to reconstruct the 3D phase-space distribution of all energetic particle orbits in the plasma. Through a transformation of the orbit distribution, the full energetic particle distribution function can be determined in the standard {energy,pitch,r,z}-space. We benchmark the technique by reconstructing the fast-ion distribution function of an MHD-quiescent DIII-D discharge using synthetic and experimental FIDA measurements. We also use the method to study the redistribution of fast ions during a sawtooth crash at ASDEX Upgrade using FIDA measurements. Finally, a comparison between the Orbit Tomography and Velocity-space Tomography is shown.

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