Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 11 of 11
Full-Text Articles in Physical Sciences and Mathematics
The Role Of Cross-Shock Potential On Pickup Ion Shock Acceleration In The Framework Of Focused Transport Theory, Pingbing Zuo, Ming Zhang, Hamid K. Rassoul
The Role Of Cross-Shock Potential On Pickup Ion Shock Acceleration In The Framework Of Focused Transport Theory, Pingbing Zuo, Ming Zhang, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
The focused transport theory is appropriate to describe the injection and acceleration of low-energy particles at shocks as an extension of diffusive shock acceleration (DSA). In this investigation, we aim to characterize the role of cross-shock potential (CSP) originated in the charge separation across the shock ramp on pickup ion (PUI) acceleration at various types of shocks with a focused transport model. The simulation results of energy spectrum and spatial density distribution for the cases with and without CSP added in the model are compared.With sufficient acceleration time, the focused transport acceleration finally falls into the DSA regime with the …
Acceleration Of Low-Energy Ions At Parallel Shocks With A Focused Transport Model, Pingbing Zuo, Ming Zhang, Hamid K. Rassoul
Acceleration Of Low-Energy Ions At Parallel Shocks With A Focused Transport Model, Pingbing Zuo, Ming Zhang, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
We present a test particle simulation on the injection and acceleration of low-energy suprathermal particles by parallel shocks with a focused transport model. The focused transport equation contains all necessary physics of shock acceleration, but avoids the limitation of diffusive shock acceleration (DSA) that requires a small pitch angle anisotropy. This simulation verifies that the particles with speeds of a fraction of to a few times the shock speed can indeed be directly injected and accelerated into the DSA regime by parallel shocks. At higher energies starting from a few times the shock speed, the energy spectrum of accelerated particles …
Stochastic Acceleration Of Suprathermal Particles Under Pressure Balance Conditions, Thorsten Antecki, Reinhard Schlickeiser, Ming Zhang
Stochastic Acceleration Of Suprathermal Particles Under Pressure Balance Conditions, Thorsten Antecki, Reinhard Schlickeiser, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
The acceleration of suprathermal charged particles in the heliosphere under pressure balance conditions including for the first time the radial spatial particle diffusion and convection in the solar wind is investigated. The physical conditions are derived for which the stationary phase space distribution of suprathermal particles approaches the power-law distribution f ∝ p −5,which is often seen in spacecraft observations. For separable source distributions in momentum and position we analytically solve the stationary particle transport equation for a radially constant solar wind speed V0 and a momentum-independent radial spatial diffusion coefficient. The resulting stationary solution at any position within the …
An Effect Of Perpendicular Diffusion On The Anisotropy Of Solar Energetic Particles From Unconnected Sources, Gang Qin, H. Q. He, Ming Zhang
An Effect Of Perpendicular Diffusion On The Anisotropy Of Solar Energetic Particles From Unconnected Sources, Gang Qin, H. Q. He, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
Recently, Tan and coworkers studied the 2001 September 24 solar energetic particle (SEP) event observed by the Wind spacecraft at 1AU and found that there is a counter-streaming particle beam with a deep depression of flux at 90° pitch angle during the beginning of the event. They suggested that it is a result of a reflecting boundary at some distance outside of 1AU. While this scenario could be true under some specific configuration of an interplanetary magnetic field, in this paper we offer another possible explanation. We simulated the SEP event by solving the five-dimensional focused transport equation numerically for …
Diffusive Compression Acceleration Of Energetic Particles With An Application To Shock Acceleration Near Injection Energies, Ming Zhang
Aerospace, Physics, and Space Science Faculty Publications
The behavior of energetic charged particles accelerated by a continuous plasma compression profile is explored in the framework of diffusion. At high enough energies, the accelerated particles have a power-law spectrum with a slope generally steeper than a shock spectrum with the same compression ratio. The spectral slope depends on the ratio of the diffusion coefficient to the product of the upstream plasma speed and the thickness of the compression region. In the limit of large diffusion, the spectrum becomes identical to that of diffusive shock acceleration, and when diffusion is small enough, it is consistent with adiabatic acceleration by …
Galactic Cosmic-Ray Modulation Using A Solar Minimum Mhd Heliosphere: A Stochastic Particle Approach, Bryan M. Ball, Ming Zhang, Hamid K. Rassoul, Timur J. Linde
Galactic Cosmic-Ray Modulation Using A Solar Minimum Mhd Heliosphere: A Stochastic Particle Approach, Bryan M. Ball, Ming Zhang, Hamid K. Rassoul, Timur J. Linde
Aerospace, Physics, and Space Science Faculty Publications
An example of Galactic cosmic-ray modulation in a fully three-dimensional heliosphere is presented here. We use a stochastic particle method to solve for modulation without requiring symmetric boundaries or fields. We include all typical modulation terms, including full three-dimensional drift. We have applied this to an MHD heliosphere appropriate for solar minimum conditions. This field includes nonradial solar wind velocity components, as well as a built-in nonspherical termination shock. Parameters that are of interest in modulation can be analyzed in detail, particularly the momentum change of cosmic rays during their transport through the heliosphere. We show radial profiles of modulation …
The Model Dependence Of Solar Energetic Particle Mean Free Paths Under Weak Scattering, Gang Qin, Joseph R. Dwyer, Hamid K. Rassoul, Glenn M. Mason
The Model Dependence Of Solar Energetic Particle Mean Free Paths Under Weak Scattering, Gang Qin, Joseph R. Dwyer, Hamid K. Rassoul, Glenn M. Mason
Aerospace, Physics, and Space Science Faculty Publications
The mean free path is widely used to measure the level of solar energetic particles' diffusive transport. We model a solar energetic particle event observed by Wind STEP at 0.31-0.62 MeV nucleonˉ¹, by solving the focused transport equation using the Markov stochastic process theory. With different functions of the pitch angle diffusion coefficient D μμ, we obtain different parallel mean free paths for the same event. We show that the different values of the mean free path are due to the high anisotropy of the solar energetic particles. This makes it problematic to use just the mean free path to …
Nonlinear Parallel And Perpendicular Diffusion Of Charged Cosmic Rays In Weak Turbulence, Andreas Schalchi, John William Bieber, William H. Matthaeus, Gang Qin
Nonlinear Parallel And Perpendicular Diffusion Of Charged Cosmic Rays In Weak Turbulence, Andreas Schalchi, John William Bieber, William H. Matthaeus, Gang Qin
Aerospace, Physics, and Space Science Faculty Publications
The problem of particle transport perpendicular to a magnetic background field is well known in cosmic-ray astrophysics. Whereas it is widely accepted that quasi-linear theory (QLT) of particle transport does not provide the correct results for perpendicular diffusion, it was assumed for a long time that QLT is the correct theory for parallel diffusion. In the current paper we demonstrate that QLT is in general also incorrect for parallel particle transport if we consider composite turbulence geometry. Motivated through the recent success of the so-called nonlinear guiding center theory of perpendicular diffusion, we present a new theory for parallel and …
Perpendicular Transport Of Solar Energetic Particles In Heliospheric Magnetic Fields, Ming Zhang, Jack Randy Jokipii, Robert Bruce Mckibben
Perpendicular Transport Of Solar Energetic Particles In Heliospheric Magnetic Fields, Ming Zhang, Jack Randy Jokipii, Robert Bruce Mckibben
Aerospace, Physics, and Space Science Faculty Publications
This paper presents direct observational evidence for large perpendicular diffusive flows of solar energetic particles in heliospheric magnetic fields. Using anisotropy measurements of 40-92 MeV protons obtained by the High-Energy Telescope of the COSPIN consortium on Ulysses at high heliographic latitudes, we find that during several gradual solar particle events, for periods of many hours, the observed particle flow is directed at significant angles to the measured local magnetic field direction, which can only be explained by cross-field diffusion. The variation of the particle flow direction with the magnetic field direction seen in the 2000 July 14 solar energetic particle …
Nonlinear Collisionless Perpendicular Diffusion Of Charged Particles, William H. Matthaeus, Gang Qin, John William Bieber, Gary Paul Zank
Nonlinear Collisionless Perpendicular Diffusion Of Charged Particles, William H. Matthaeus, Gang Qin, John William Bieber, Gary Paul Zank
Aerospace, Physics, and Space Science Faculty Publications
A nonlinear theory of the perpendicular diffusion of charged particles is presented, including the influence of parallel scattering and dynamical turbulence. The theory shows encouraging agreement with numerical simulations.
Perpendicular Transport Of Charged Particles In Composite Model Turbulence: Recovery Of Diffusion, Gang Qin, William H. Matthaeus, John William Bieber
Perpendicular Transport Of Charged Particles In Composite Model Turbulence: Recovery Of Diffusion, Gang Qin, William H. Matthaeus, John William Bieber
Aerospace, Physics, and Space Science Faculty Publications
The computation of charged particle orbits in model turbulent magnetic fields is used to investigate the properties of particle transport in the directions perpendicular to the large-scale magnetic field. Recent results by Qin, Matthaeus, & Bieber demonstrate that parallel scattering suppresses perpendicular diffusion to a subdiffusive level when the turbulence lacks transverse structure. Here numerical computations are used to show that in turbulence in which there is substantial transverse structure, a second regime of diffusive transport can be established. In both the subdiffusion regime and this "second diffusion" regime, perpendicular transport is intrinsically nonlinear. The regime of second diffusion persists …