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Title: Radial diffusion in non-dipolar background fields

  1. Los Alamos National Laboratory
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Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program
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DOE Contract Number:
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Resource Relation:
Conference: Geospace Environment Modelling (GEM) workshop ; 2016-06-20 - 2016-06-24 ; Santa Fe, New Mexico, United States
Country of Publication:
United States
Heliospheric and Magnetospheric Physics; radiation belts, radial diffusion

Citation Formats

Cunningham, Gregory Scott. Radial diffusion in non-dipolar background fields. United States: N. p., 2016. Web.
Cunningham, Gregory Scott. Radial diffusion in non-dipolar background fields. United States.
Cunningham, Gregory Scott. 2016. "Radial diffusion in non-dipolar background fields". United States. doi:.
title = {Radial diffusion in non-dipolar background fields},
author = {Cunningham, Gregory Scott},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 6

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  • This document describes radial diffusion and its impact on modeling radiation belt dynamics.
  • The spin-temperature treatment used in solid-state NMR spectroscopy and the statistical treatment used in electron spin-echo (ESE) spectroscopy are compared. The statistical treatment is shown to be an exact solution of a multispin Hamiltonian with certain bilinear terms treated as relaxation processes. The magnitude of the dipolar field and its autocorrelation function have been identified in both treatments. This allows the transfer of experimental data on electron dipolar fields to nuclear spin systems in solids containing large numbers of paramagnetic centers. Measurements of the dipolar field and its relaxation time are demonstrated on samples from the Argonne Premium Coal Samplemore » program. Even brief exposure to air has significant effects on the electron-spin dynamics. Sample preparation is an important aspect of magnetic resonance experiments on coal. 11 refs.« less
  • A model for radial diffusion caused by electromagnetic disturbances was published by Falthammar (1965) using a two-parameter model of the disturbance perturbing a background dipole magnetic field. Schulz and Lanzerotti (1974) extended this model by recognizing the two parameter perturbation as the leading (non--dipole) terms of the Mead Williams magnetic field model. They emphasized that the magnetic perturbation in such a model induces an electric ield that can be calculated from the motion of field lines on which the particles are ‘frozen’. Roederer and Zhang (2014) describe how the field lines on which the particles are frozen can be calculatedmore » by tracing the unperturbed field lines from the minimum-B location to the ionospheric footpoint, and then tracing the perturbed field (which shares the same ionospheric footpoint due to the frozen -in condition) from the ionospheric footpoint back to a perturbed minimum B location. The instantaneous change n Roederer L*, dL*/dt, can then be computed as the product (dL*/dphi)*(dphi/dt). dL*/Dphi is linearly dependent on the perturbation parameters (to first order) and is obtained by computing the drift across L*-labeled perturbed field lines, while dphi/dt is related to the bounce-averaged gradient-curvature drift velocity. The advantage of assuming a dipole background magnetic field, as in these previous studies, is that the instantaneous dL*/dt can be computed analytically (with some approximations), as can the DLL that results from integrating dL*/dt over time and computing the expected value of (dL*)^2. The approach can also be applied to complex background magnetic field models like T89 or TS04, on top of which the small perturbations are added, but an analytical solution is not possible and so a numerical solution must be implemented. In this talk, I discuss our progress in implementing a numerical solution to the calculation of DL*L* using arbitrary background field models with simple electromagnetic perturbations.« less