Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session JM9: Mini-Conference: Van Allen 100: Cosmic Ray Transport |
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Chair: Gregory Howes, University of Iowa Room: Salon ABC |
Tuesday, October 28, 2014 2:00PM - 2:35PM |
JM9.00001: Cosmic ray transport in the heliosphere Reinhard Schlickeiser Since the development of satellite space technology about 50 years ago the solar heliosphere is explored almost routinely by several spacecrafts carrying detectors for measuring the properties of the interplanetary medium including energetic charged particles (cosmic rays), solar wind particle densities and electromagnetic fields. In 2012 the Voyager 1 spacecraft has even left what could be described as the heliosphere modulation region, as indicated by the sudden disappearance of low energy heliospheric cosmic ray particles. As other dilute cosmic plasmas have similar densities, temperatures and magnetic fields as the solar wind, the physical processes there probably are the same. With the available in-situ measurements of interplanetary turbulent electromagnetic fields and of the momentum spectra of different cosmic ray species in different interplanetary environments, the heliosphere is the best space laboratory to test our understanding of the transport and acceleration of cosmic rays in space plasmas. I review both, the historical development and the current state of various cosmic ray transport equations. Similarities and differences to gyrokinetic transport equations for terrestrial fusion plasmas are highlighted. [Preview Abstract] |
Tuesday, October 28, 2014 2:35PM - 3:10PM |
JM9.00002: Where is the cosmic-ray modulation boundary of the heliosphere? Ming Zhang, Konstantin Gamayunov, Hamid Rassoul, Nikolai Pogorelov When cosmic rays (CRs) propagate through the heliosphere, they must overcome the effects of outgoing solar wind (SW), which results in CR modulation. Studies found that the modulation occurs mainly through adiabatic energy loss in the supersonic SW. We had expected it would cease beyond the termination shock, but CR modulation continues in the inner heliosheath. This is because CRs detected there have already spent time in the SW. In a similar argument, CRs seen outside of the heliopause should still be modulated, rendering no precise modulation boundary. However, recent observations from Voyager 1 show that CR flux has reached its interstellar level almost immediately after the heliopause. To understand the difference between the inner and outer heliosheath, we have to consider the huge difference of particle transport in the heliospheric turbulence and interstellar turbulence. Due to the low level of interstellar turbulence inferred from IBEX observations, we expect the parallel diffusion to increase from its typical heliospheric value of $10^{23}$ cm$^2$/s to the interstellar value of $> 10^{27}$ cm$^2$/s, while the perpendicular diffusion decreases significantly. Here we present model results that show the CR modulation boundary should be slightly beyond the heliopause. [Preview Abstract] |
Tuesday, October 28, 2014 3:10PM - 3:45PM |
JM9.00003: Cosmic Ray Self-Confinement, Escape and Transport Mikhail Malkov Propagation of cosmic rays (CR) in a self-confinement regime is discussed. A self-similar solution for a CR-cloud expansion along the magnetic field strongly deviates from test-particle results. The normalized CR partial pressure is close to $\mathcal{P}\left(p,z,t\right)=2\left[\left|z\right|^{5/3}+z_{{\rm dif}}^{5/3}\left(p,t\right)\right]^{-3/5}\exp\left[-z^{2}/4D_{B}\left(p\right)t\right]$, where $p$ is the momentum of CR and $z$ is directed along the field. The core of the cloud expands as $z_{dif}\propto\sqrt{D_{ NL}\left(p\right)t}$ and decays in time as $\mathcal{P}\propto2z_{dif}^{-1}\left(t\right)$. The diffusion coefficient $D_{NL}$ is strongly suppressed compared to its background value $D_{{\rm B}}$: $D_{{\rm NL}}\sim D_{{\rm B}}\exp\left(-\Pi\right)\ll D_{{\rm B}}$ for sufficiently high field-line-integrated CR partial pressure, $\Pi$. When $\Pi\gg1$, the CRs drive Alfven waves efficiently enough to build a $\it{transport~barrier}$ ($\mathcal{P}\approx2/\left|z\right|$ -``pedestal'') that strongly reduces the leakage. The solution has a spectral break in momentum spectrum at $p=p_{{\rm br}}$, where $p_{{\rm br}}$ satisfies the following equation $D_{{\rm NL}}\left(p_{{\rm br}}\right)\simeq z^{2}/t$. Magnetic focusing effects in CR transport are briefly discussed. [Preview Abstract] |
Tuesday, October 28, 2014 3:45PM - 4:05PM |
JM9.00004: On Cosmic Ray Propagation Mikhail Medvedev Cosmic ray propagation is diffusive because of pitch angle scattering by waves. We demonstrate that if the high-amplitude magnetic turbulence with $\delta B/B \sim 1$ is present on top of the mean field gradient, the diffusion becomes asymmetric. As an example, we solve this diffusion problem in one dimension analytically with a Markov chain analysis. The cosmic ray density markedly differs from the standard diffusion prediction. The equation for the continuous limit is also derived, which shows limitations of the convection-diffusion equation. We also explore how the difference of the diffusion coefficient for positively and negatively charged species may affect their distribution throughout the system (e.g., galaxy, heliosphere). The result is mostly relevant to low energy particles. The implications of the results are discussed. The results are mostly relevant to fairly low-energy cosmic rays. However, they are general enough to be applicable to any particle transport, not just cosmic rays. [Preview Abstract] |
Tuesday, October 28, 2014 4:05PM - 4:25PM |
JM9.00005: Non-Maxwellian Core-electron Distribution Functions in the Solar Wind Manish Mithaiwala, Leonid Rudakov, Gurudas Ganguli, Chris Crabtree Electron velocity distribution functions in the solar wind are generally characterized by a thermal ``core,'' a superthermal ``halo,'' and field aligned `strahl' electrons. The core distribution is mostly modeled as a bi-Maxwellian distribution, even though the solar wind is nearly collisonless and kinetic wave-particle interactions are expected to be dominant. It has been shown that the non-linear scattering (NLS) by plasma particles due to Landau resonance with beat waves play a fundamental role for low-beta magnetospheric plasmas [1, 2]. However for high-beta solar-wind plasma the rate of the linear Landau damping by electrons with a Maxwellian distribution could prevail over NLS [3]. Furthermore in the high-beta solar wind plasma kinetic Alfven wave (KAW) and whistler waves meet the Landau resonance with electrons for velocities less than the electron thermal speed and greater than the Alfven speed. The measured spectrum of KAW fluctuations in the turbulent solar wind plasma is used to calculate the electron distribution functions resulting from quasi-linear diffusion. Quasi-linear diffusion establishes a step-like profile in the electron distribution function for parallel velocity for speeds larger than the Alfven speed. For parallel velocities less than the Alfven velocity, evolution of the distribution due to the beat resonance of waves is considered. [1] Ganguli et al., (2010) \textit{Phys. Plasmas} \textbf{17}, 052310; [2] Rudakov et al., (2011) \textit{Phys. Plasma}, \textbf{18}, 012307; [3] Mithaiwala et al., (2012) \textit{Phys. Plasmas}, \textbf{18}, 055710 [Preview Abstract] |
Tuesday, October 28, 2014 4:25PM - 4:45PM |
JM9.00006: Magnetic pumping of the solar wind Jan Egedal, Emily Lichko, William Daughton The transport of matter and radiation in the solar wind and terrestrial magnetosphere is a complicated problem involving competing processes of charged particles interacting with electric and magnetic fields. Given the rapid expansion of the solarwind, it would be expected that superthermal electrons originating in the corona would cool rapidly as a function of distance to the Sun. However, this is not observed, and various models have been proposed as plausible candidates for heating the solar wind as it super-sonically streams away from the sun. In the compressional pumping mechanism explored by Fisk \& Gloeckler particles are accelerated by random compressions by the interplanetary wave turbulence. This theory explores diffusion due to spatial non-uniformities and provides a mechanism for redistributing particle. For investigation of a related but different heating mechanism, magnetic pumping, in our work we include diffusion of anisotropic features that develops in velocity space. The mechanism allows energy to be transferred to the particles directly from the turbulence. The efficiency of the process is explored using kinetic simulations. [Preview Abstract] |
Tuesday, October 28, 2014 4:45PM - 5:00PM |
JM9.00007: Magnetic Reconnection in the Earth Magnetotail and Auroral Substorms* B. Basu, B. Coppi By now it is well-accepted that magnetic reconnection is responsible for the generation of accelerated particle populations in space, such as that proposed to occur in the Earth's magnetotail [1] and generate auroral substorms. In fact, reconnection is the most probable process to explain the observed high-energy particle populations at the edge of the Heliosphere. On the other hand, the theory of this process remains in need of further attention. Since the late sixties, it has been known that departures from Maxwellian distributions for the background plasmas, such as anisotropic electron temperatures, have an important effect on the growth rate of modes producing reconnection. However, the significant effect of transverse (to the field) electron temperature gradients has yet to be included in the theory. The relationship, between the theory of reconnecting modes emerging from plane one-dimensional neutral sheets and modes emerging from cylindrical and axisymmetric toroidal laboratory plasmas, is discussed. In the latter case, a wealth of relevant experimental observations is available. *Sponsored in part by the US DOE.\\[4pt] [1] B. Coppi, G. Laval, and R. Pellat, \textit{Phys. Rev. Lett}. \textbf{16}, 1207 (1966). [Preview Abstract] |
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