Determining pitch-angle diffusion coefficients from test particle simulations

Journal Article · Tue Dec 20 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/833/2/223· OSTI ID:22869655

Ivascenko, Alex; Spanier, Felix ^[1]; Lange, Sebastian ^[2]; Vainio, Rami ^[3]

---

1. Centre for Space Research, North-West University, 2531 Potchefstroom (South Africa)
2. Lehrstuhl für Astronomie, Universität Würzburg, Emil-Fischer Str. 31, D-97074 Würzburg (Germany)
3. Department of Physics and Astronomy, University of Turku (Finland)

The transport and acceleration of charged particles in turbulent media are topics of great interest in space physics and interstellar astrophysics. These processes are dominated by the scattering of particles off magnetic irregularities. The scattering process itself is usually described by small-angle scattering, with the pitch-angle coefficient D{sub μμ} playing a major role. Since the diffusion coefficient D{sub μμ} can be determined analytically only for the approximation of quasilinear theory, the determination of this coefficient from numerical simulations has become more important. So far these simulations have yielded particle tracks for small-scale scattering, which can then be interpreted using the running diffusion coefficients. This method has a limited range of validity. This paper presents two new methods that allow for the calculation of the pitch-angle diffusion coefficient from numerical simulations. These methods no longer analyze particle trajectories and instead examine the change of particle distribution functions. It is shown that these methods provide better resolved results and allow for the analysis of strong turbulence. The application of these methods to Monte Carlo simulations of particle scattering and hybrid MHD-particle simulations is presented. Both analysis methods are able to recover the diffusion coefficients used as input for the Monte Carlo simulations and provide better results in MHD simulations, especially for stronger turbulence.

• OSTI ID: 22869655
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 833; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
APPROXIMATIONS
ASTROPHYSICS
CHARGED PARTICLES
COMPUTERIZED SIMULATION
DIFFUSION
DISTRIBUTION FUNCTIONS
INCLINATION
MAGNETOHYDRODYNAMICS
MONTE CARLO METHOD
QUASILINEAR PROBLEMS
SMALL ANGLE SCATTERING
SPACE
TURBULENCE