Hybrid Vlasov simulations for alpha particles heating in the solar wind

AbstractHeating and acceleration of heavy ions in the solar wind and corona represent a long-standing theoretical problem in space physics and are distinct experimental signatures of kinetic processes occurring in collisionless plasmas. To address this problem, we propose the use of a low-noise hybrid-Vlasov code in four dimensional phase space (1D in physical space and 3D in velocity space) configuration. We trigger a turbulent cascade injecting the energy at large wavelengths and analyze the role of kinetic effects along the development of the energy spectra. Following the evolution of both proton and α distribution functions shows that both the ion species significantly depart from the maxwellian equilibrium, with the appearance of beams of accelerated particles in the direction parallel to the background magnetic field.

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Low-frequency Whistler Waves Modulate Electrons and Generate Higher-frequency Whistler Waves in the Solar Wind

The Astrophysical Journal ◽

10.3847/1538-4357/ac2e97 ◽

2021 ◽

Vol 923 (2) ◽

pp. 216

Author(s):

S. T. Yao ◽

Q. Q. Shi ◽

Q. G. Zong ◽

A. W. Degeling ◽

R. L. Guo ◽

...

Keyword(s):

Solar Wind ◽

Electromagnetic Fields ◽

Low Frequency ◽

Space Physics ◽

Lower Hybrid ◽

High Temporal Resolution ◽

Modulation Amplitude ◽

Whistler Waves ◽

Direction Parallel ◽

Background Magnetic Field

Abstract The role of whistler-mode waves in the solar wind and the relationship between their electromagnetic fields and charged particles is a fundamental question in space physics. Using high-temporal-resolution electromagnetic field and plasma data from the Magnetospheric MultiScale spacecraft, we report observations of low-frequency whistler waves and associated electromagnetic fields and particle behavior in the Earth’s foreshock. The frequency of these whistler waves is close to half the lower-hybrid frequency (∼2 Hz), with their wavelength close to the ion gyroradius. The electron bulk flows are strongly modulated by these waves, with a modulation amplitude comparable to the solar wind velocity. At such a spatial scale, the electron flows are forcibly separated from the ion flows by the waves, resulting in strong electric currents and anisotropic ion distributions. Furthermore, we find that the low-frequency whistler wave propagates obliquely to the background magnetic field ( B 0), and results in spatially periodic magnetic gradients in the direction parallel to B 0. Under such conditions, large pitch-angle electrons are trapped in wave magnetic valleys by the magnetic mirror force, and may provide free perpendicular electron energy to excite higher-frequency whistler waves. This study offers important clues and new insights into wave–particle interactions, wave generation, and microscale energy conversion processes in the solar wind.

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TAUS measurements of non-gyrotropic distribution functions of solar wind alpha particles

10.1063/1.51484 ◽

1996 ◽

Author(s):

H. F. Astudillo ◽

E. Marsch ◽

S. Livi ◽

H. Rosenbauer

Keyword(s):

Solar Wind ◽

Distribution Functions ◽

Alpha Particles

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Study of alpha particle properties across rarefaction regions

10.5194/egusphere-egu21-2864 ◽

2021 ◽

Author(s):

Tereza Durovcova ◽

Jana Šafránková ◽

Zdeněk Němeček

Keyword(s):

Solar Wind ◽

Wind Speed ◽

Alpha Particle ◽

Solar Wind Speed ◽

Coronal Holes ◽

Distribution Functions ◽

Alpha Particles ◽

Slow Solar Wind ◽

The Sun ◽

Wind Source

Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.

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Collisionless energy transfer in kinetic turbulence: field–particle correlations in Fourier space

Journal of Plasma Physics ◽

10.1017/s0022377819000515 ◽

2019 ◽

Vol 85 (4) ◽

Author(s):

Tak Chu Li ◽

Gregory G. Howes ◽

Kristopher G. Klein ◽

Yi-Hsin Liu ◽

Jason M. TenBarge

Keyword(s):

Solar Wind ◽

Energy Transfer ◽

Low Frequency ◽

Particle Energy ◽

Distribution Functions ◽

Velocity Space ◽

Correlation Technique ◽

Direction Parallel ◽

Particle Correlation ◽

Particle Correlations

Turbulence is commonly observed in nearly collisionless heliospheric plasmas, including the solar wind and corona and the Earth’s magnetosphere. Understanding the collisionless mechanisms responsible for the energy transfer from the turbulent fluctuations to the particles is a frontier in kinetic turbulence research. Collisionless energy transfer from the turbulence to the particles can take place reversibly, resulting in non-thermal energy in the particle velocity distribution functions (VDFs) before eventual collisional thermalization is realized. Exploiting the information contained in the fluctuations in the VDFs is valuable. Here we apply a recently developed method based on VDFs, the field–particle correlation technique, to a $\unicode[STIX]{x1D6FD}=1$ , solar-wind-like, low-frequency Alfvénic turbulence simulation with well-resolved phase space to identify the field–particle energy transfer in velocity space. The field–particle correlations reveal that the energy transfer, mediated by the parallel electric field, results in significant structuring of the VDF in the direction parallel to the magnetic field. Fourier modes representing the length scales between the ion and electron gyroradii show that energy transfer is resonant in nature, localized in velocity space to the Landau resonances for each Fourier mode. The energy transfer closely follows the Landau resonant velocities with varying perpendicular wavenumber $k_{\bot }$ and plasma $\unicode[STIX]{x1D6FD}$ . This resonant signature, consistent with Landau damping, is observed in all diagnosed Fourier modes that cover the dissipation range of the simulation.

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A kinetic model of plasma turbulence

Journal of Plasma Physics ◽

10.1017/s0022377814000841 ◽

2014 ◽

Vol 81 (1) ◽

Cited By ~ 95

Author(s):

S. Servidio ◽

F. Valentini ◽

D. Perrone ◽

A. Greco ◽

F. Califano ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Velocity Distribution Function ◽

Plasma Turbulence ◽

Alpha Particles ◽

Magnetic Field Direction ◽

Temperature Anisotropy ◽

Kinetic Effects ◽

Magnetic Gradients ◽

Definition Of

A Hybrid Vlasov–Maxwell (HVM) model is presented and recent results about the link between kinetic effects and turbulence are reviewed. Using five-dimensional (2D in space and 3D in the velocity space) simulations of plasma turbulence, it is found that kinetic effects (or non-fluid effects) manifest through the deformation of the proton velocity distribution function (DF), with patterns of non-Maxwellian features being concentrated near regions of strong magnetic gradients. The direction of theproper temperature anisotropy, calculated in the main reference frame of the distribution itself, has a finite probability of being along or across the ambient magnetic field, in general agreement with the classical definition of anisotropyT⊥/T∥(where subscripts refer to the magnetic field direction). Adopting the latter conventional definition, by varying the global plasma beta (β) and fluctuation level, simulations explore distinct regions of the space given byT⊥/T∥and β∥, recovering solar wind observations. Moreover, as in the solar wind, HVM simulations suggest that proton anisotropy is not only associated with magnetic intermittent events, but also with gradient-type structures in the flow and in the density. The role of alpha particles is reviewed using multi-ion kinetic simulations, revealing a similarity between proton and helium non-Maxwellian effects. The techniques presented here are applied to 1D spacecraft-like analysis, establishing a link between non-fluid phenomena and solar wind magnetic discontinuities. Finally, the dimensionality of turbulence is investigated, for the first time, via 6D HVM simulations (3D in both spaces). These preliminary results provide support for several previously reported studies based on 2.5D simulations, confirming several basic conclusions. This connection between kinetic features and turbulence open a new path on the study of processes such as heating, particle acceleration, and temperature-anisotropy, commonly observed in space plasmas.

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Electrostatic Waves with Rapid Frequency Shifts in the Solar Wind Sunward of 1/3 AU

10.5194/egusphere-egu21-16103 ◽

2021 ◽

Author(s):

Lily Kromyda ◽

David M. Malaspina ◽

Robert E. Ergun ◽

Jasper Halekas ◽

Michael L. Stevens ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Plasma Wave ◽

Detection Algorithm ◽

Space Physics ◽

University Of California ◽

Magnetic Fluctuations ◽

Plasma Parameters ◽

University Of Colorado ◽

Background Magnetic Field

During its first five orbits, the FIELDS plasma wave investigation on board Parker Solar Probe (PSP)&#160; has observed a multitude of plasma waves, including electrostatic whistler and electron Bernstein waves (Malaspina et al. 2020), sunward propagating whistlers (Agapitov et al. 2020), ion-scale electromagnetic waves (Verniero et al. 2020, Bowen et al. 2020) and Alfven, slow and fast mode waves (Chaston et al. 2020).The importance of these waves lies in their potential to redistribute the energy of the solar wind among different particles species (wave-particle interactions) or different types of waves (wave-wave interactions). The abundance of waves and instabilities observed with PSP points to their central role in the regulation of this energy exchange.Here we present first observations of an intermittent, electrostatic and broadband plasma wave that is ubiquitous in the range of distances that PSP has probed so far. A unique feature of these waves (FDWs) is a frequency shift that occurs on millisecond timescales. In the frame of the spacecraft, FDWs usually appear between the electron cyclotron and electron plasma frequencies.We develop a detection algorithm that identifies the FDWs in low cadence spectra. We analyze them using various statistical techniques. We establish their phenomenology and compare the magnetic fluctuations of the background magnetic field at times of FDWs and at times without FDWs. We establish their polarization with respect to the background magnetic field and search for correlations with various plasma parameters and features in the electron, proton and alpha particle distribution moments. We also investigate possible plasma wave modes that could be responsible for the growth of FDWs and the instability mechanisms that could be generating them.&#160;Lily Kromyda*(1), David M. Malaspina (1,2), Robert E. Ergun(1,2) , Jasper Halekas(3), Michael L. Stevens(4) , Jennifer Verniero(5), Alexandros Chasapis(2) , Daniel Vech(2) , Stuart D. Bale(5,6) , John W. Bonnell(5) , Thierry Dudok de Wit(7) , Keith Goetz(8) , Katherine Goodrich(5) , Peter R. Harvey(5) , Robert J. MacDowall(9) , Marc Pulupa(5) , Anthony W. Case(4) , Justin C. Kasper(10) , Kelly E. Korreck(4) , Davin Larson(5) , Roberto Livi(5) , Phyllis Whittlesey(5)(1) Astrophysical and Planetary Sciences Department, University of Colorado, Boulder, CO, USA(2) Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA(3) &#160;University of Iowa, Iowa City, IA, USA(4) Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA(5) &#160;Space Sciences Laboratory, University of California, Berkeley, CA, USA(6) Physics Department, University of California, Berkeley, CA, USA(7) &#160;LPC2E, CNRS, and University of Orleans, Orleans, France(8) &#160;School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA(9) &#160;NASA Goddard Space Flight Center, Greenbelt, MD, USA(10) University of Michigan, Ann Arbor, MI, USA

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Alpha particle thermodynamics in the inner heliosphere fast solar wind

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834900 ◽

2019 ◽

Vol 623 ◽

pp. L2 ◽

Cited By ~ 12

Author(s):

D. Stansby ◽

D. Perrone ◽

L. Matteini ◽

T. S. Horbury ◽

C. S. Salem

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Alpha Particle ◽

Distribution Functions ◽

Alpha Particles ◽

Perpendicular Direction ◽

The Sun ◽

Fast Solar Wind ◽

Field Parallel ◽

The Magnetic Field

Context. Plasma processes occurring in the corona and solar wind can be probed by studying the thermodynamic properties of different ion species. However, most in situ observations of positive ions in the solar wind are taken at 1 AU, where information on their solar source properties may have been irreversibly erased. Aims. In this study we aim to use the properties of alpha particles at heliocentric distances between 0.3 AU and 1 AU to study plasma processes occurring at the points of observation, and to infer processes occurring inside 0.3 AU by comparing our results to previous remote sensing observations of the plasma closer to the Sun. Methods. We reprocessed the original Helios positive ion distribution functions, isolated the alpha particle population, and computed the alpha particle number density, velocity, and magnetic field perpendicular and parallel temperatures. We then investigated the radial variation of alpha particle temperatures in fast solar wind observed between 0.3 AU and 1 AU. Results. Between 0.3 AU and 1 AU alpha particles are heated in the magnetic field perpendicular direction and cooled in the magnetic field parallel direction. Alpha particle evolution is bounded by the alpha firehose instability threshold, which provides one possible mechanism to explain the observed parallel cooling and perpendicular heating. Closer to the Sun our observations suggest that the alpha particles undergo heating in the perpendicular direction, whilst the large magnetic field parallel temperatures observed at 0.3 AU may be due to the combined effect of double adiabatic expansion and alpha particle deceleration inside 0.3 AU.

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Reflection-driven magnetohydrodynamic turbulence in the solar atmosphere and solar wind

Journal of Plasma Physics ◽

10.1017/s0022377819000540 ◽

2019 ◽

Vol 85 (4) ◽

Cited By ~ 13

Author(s):

Benjamin D. G. Chandran ◽

Jean C. Perez

Keyword(s):

Solar Wind ◽

Heating Rate ◽

Three Dimensional ◽

Power Spectra ◽

Inertial Range ◽

Magnetic Flux Tube ◽

Analytic Model ◽

Mhd Turbulence ◽

Background Magnetic Field ◽

Turbulent Heating

We present three-dimensional direct numerical simulations and an analytic model of reflection-driven magnetohydrodynamic (MHD) turbulence in the solar wind. Our simulations describe transverse, non-compressive MHD fluctuations within a narrow magnetic flux tube that extends from the photosphere, through the chromosphere and corona and out to a heliocentric distance $r$ of 21 solar radii $(R_{\odot })$ . We launch outward-propagating ‘ $\boldsymbol{z}^{+}$ fluctuations’ into the simulation domain by imposing a randomly evolving photospheric velocity field. As these fluctuations propagate away from the Sun, they undergo partial reflection, producing inward-propagating ‘ $\boldsymbol{z}^{-}$ fluctuations’. Counter-propagating fluctuations subsequently interact, causing fluctuation energy to cascade to small scales and dissipate. Our analytic model incorporates dynamic alignment, allows for strongly or weakly turbulent nonlinear interactions and divides the $\boldsymbol{z}^{+}$ fluctuations into two populations with different characteristic radial correlation lengths. The inertial-range power spectra of $\boldsymbol{z}^{+}$ and $\boldsymbol{z}^{-}$ fluctuations in our simulations evolve toward a $k_{\bot }^{-3/2}$ scaling at $r>10R_{\odot }$ , where $k_{\bot }$ is the wave-vector component perpendicular to the background magnetic field. In two of our simulations, the $\boldsymbol{z}^{+}$ power spectra are much flatter between the coronal base and $r\simeq 4R_{\odot }$ . We argue that these spectral scalings are caused by: (i) high-pass filtering in the upper chromosphere; (ii) the anomalous coherence of inertial-range $\boldsymbol{z}^{-}$ fluctuations in a reference frame propagating outwards with the $\boldsymbol{z}^{+}$ fluctuations; and (iii) the change in the sign of the radial derivative of the Alfvén speed at $r=r_{\text{m}}\simeq 1.7R_{\odot }$ , which disrupts this anomalous coherence between $r=r_{\text{m}}$ and $r\simeq 2r_{\text{m}}$ . At $r>1.3R_{\odot }$ , the turbulent heating rate in our simulations is comparable to the turbulent heating rate in a previously developed solar-wind model that agreed with a number of observational constraints, consistent with the hypothesis that MHD turbulence accounts for much of the heating of the fast solar wind.

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HelioSwarm: The Nature of Turbulence in Space Plasmas

10.5194/egusphere-egu21-12092 ◽

2021 ◽

Author(s):

Harlan Spence ◽

Kristopher Klein ◽

HelioSwarm Science Team

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Solar Wind Plasma ◽

Turbulent Energy ◽

Space Plasmas ◽

Plasma Parameters ◽

Astrophysical Plasmas ◽

Ion Distributions ◽

Background Magnetic Field

Recently selected for phase A study for NASA&#8217;s Heliophysics MidEx Announcement of Opportunity, the HelioSwarm Observatory proposes to transform our understanding of the physics of turbulence in space and astrophysical plasmas by deploying nine spacecraft to measure the local plasma and magnetic field conditions at many points, with separations between the spacecraft spanning MHD and ion scales.&#160;&#160;HelioSwarm resolves the transfer and dissipation of turbulent energy in weakly-collisional magnetized plasmas with a novel configuration of spacecraft in the solar wind. These simultaneous multi-point, multi-scale measurements of space plasmas allow us to reach closure on two science goals comprised of six science objectives: (1) reveal how turbulent energy is transferred in the most probable, undisturbed solar wind plasma and distributed as a function of scale and time; (2) reveal how this turbulent cascade of energy varies with the background magnetic field and plasma parameters in more extreme solar wind environments; (3) quantify the transfer of turbulent energy between fields, flows, and ion heat; (4) identify thermodynamic impacts of intermittent structures on ion distributions; (5) determine how solar wind turbulence affects and is affected by large-scale solar wind structures; and (6) determine how strongly driven turbulence differs from that in the undisturbed solar wind.&#160;

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Proton Beam Abundance Variations and Their Relation to Alpha Particle Properties

The Astrophysical Journal ◽

10.3847/1538-4357/ac2c03 ◽

2021 ◽

Vol 923 (2) ◽

pp. 170

Author(s):

Tereza Ďurovcová ◽

Jana Šafránková ◽

Zdeněk Němeček

Keyword(s):

Solar Wind ◽

Proton Beam ◽

Alpha Particle ◽

Source Region ◽

Radial Distance ◽

Alpha Particles ◽

Momentum Balance ◽

Particle Interactions ◽

Coulomb Collisions ◽

Particle Properties

Abstract Less abundant but still dynamically important solar wind components are the proton beam and alpha particles, which usually contribute similarly to the total ion momentum. The main characteristics of alpha particles are determined by the solar wind source region, but the origin of the proton beam and its properties are still not fully explained. We use the plasma data measured in situ on the path from 0.3 to 1 au (Helios 1 and 2) and focus on the proton beam development with an increasing radial distance as well as on the connection between the proton beam and alpha particle properties. We found that the proton beam relative abundance increases with increasing distance from the Sun in the collisionally young streams. Among the mechanisms suggested for beam creation, we have identified the wave–particle interactions with obliquely propagating Alfvén modes being consistent with observations. As the solar wind streams get collisionally older, the proton beam decay gradually dominates and the beam abundance is reduced. In search for responsible mechanisms, we found that the content of alpha particles is correlated with the proton beam abundance, and this effect is more pronounced in the fast solar wind streams during the solar maximum. We suggest that Coulomb collisions are the main agent leading to merging of the proton beam and core. We are also showing that the variations of the proton beam abundance are correlated with a decrease of the alpha particle velocity in order to maintain the total momentum balance in the solar wind frame.

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