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Title: Neoclassical Diffusion of Radiation-Belt Electrons Across Very Low L -shells

Abstract

In the presence of drift-shell splitting intrinsic to the IGRF magnetic field model, pitch-angle scattering from Coulomb collisions experienced by radiation-belt electrons in the upper atmosphere and ionosphere produces extra radial diffusion, a form of neoclassical diffusion. The strength of the neoclassical radial diffusion at L < 1.2 exceeds that expected there from radial-diffusion mechanisms traditionally considered, and decreases with increasing L-shell. In this study we construct a numerical model for this coupled (radial and pitch-angle) collisional diffusion process and apply it to simulate raw count-rate data observed aboard the Gemini spacecraft for several years after the 1962 Starfish nuclear detonation. The data show apparent lifetimes 10-100 times as long as would have been expected from collisional pitch-angle diffusion and Coulomb drag alone. Our model reproduces apparent lifetimes for >0.5-MeV electrons in the region 1.14 < L < 1.26 to within a factor of two (comparable to the uncertainty quoted for the observations). We conclude that neoclassical radial diffusion (resulting from drift-shell splitting intrinsic to IGRF's azimuthal asymmetries) mitigates the decay expected from collisional pitch-angle diffusion and inelastic energy loss alone and thus contributes importantly to the long apparent lifetimes observed at these low L-shells.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [2];  [3]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Space Science and Applications
  2. French Alternative Energies and Atomic Energy Commission (CEA) Military Applications Dept. (DAM) Ile-de-France (DIF), Arpajon (France)
  3. Lockheed Martin Corp., Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP) (NA-10); Defense Threat Reduction Agency (DTRA); French Alternative Energies and Atomic Energy Commission (CEA) Military Applications Dept. (DAM); Directorate-General for Armaments (DGA)
OSTI Identifier:
1432624
Report Number(s):
LA-UR-17-29808
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396; DTRA10027-19910
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Name: Journal of Geophysical Research. Space Physics; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; neoclassical diffusion; radial diffusion; artificial radiation belts; neoclassical transport across low L-shells; Coulomb collisions; Fokker-Planck equation; IGRF

Citation Formats

Cunningham, Gregory S., Loridan, Vivien, Ripoll, Jean-Francois, and Schulz, Michael. Neoclassical Diffusion of Radiation-Belt Electrons Across Very Low L -shells. United States: N. p., 2018. Web. doi:10.1002/2017JA024931.
Cunningham, Gregory S., Loridan, Vivien, Ripoll, Jean-Francois, & Schulz, Michael. Neoclassical Diffusion of Radiation-Belt Electrons Across Very Low L -shells. United States. doi:10.1002/2017JA024931.
Cunningham, Gregory S., Loridan, Vivien, Ripoll, Jean-Francois, and Schulz, Michael. Fri . "Neoclassical Diffusion of Radiation-Belt Electrons Across Very Low L -shells". United States. doi:10.1002/2017JA024931.
@article{osti_1432624,
title = {Neoclassical Diffusion of Radiation-Belt Electrons Across Very Low L -shells},
author = {Cunningham, Gregory S. and Loridan, Vivien and Ripoll, Jean-Francois and Schulz, Michael},
abstractNote = {In the presence of drift-shell splitting intrinsic to the IGRF magnetic field model, pitch-angle scattering from Coulomb collisions experienced by radiation-belt electrons in the upper atmosphere and ionosphere produces extra radial diffusion, a form of neoclassical diffusion. The strength of the neoclassical radial diffusion at L < 1.2 exceeds that expected there from radial-diffusion mechanisms traditionally considered, and decreases with increasing L-shell. In this study we construct a numerical model for this coupled (radial and pitch-angle) collisional diffusion process and apply it to simulate raw count-rate data observed aboard the Gemini spacecraft for several years after the 1962 Starfish nuclear detonation. The data show apparent lifetimes 10-100 times as long as would have been expected from collisional pitch-angle diffusion and Coulomb drag alone. Our model reproduces apparent lifetimes for >0.5-MeV electrons in the region 1.14 < L < 1.26 to within a factor of two (comparable to the uncertainty quoted for the observations). We conclude that neoclassical radial diffusion (resulting from drift-shell splitting intrinsic to IGRF's azimuthal asymmetries) mitigates the decay expected from collisional pitch-angle diffusion and inelastic energy loss alone and thus contributes importantly to the long apparent lifetimes observed at these low L-shells.},
doi = {10.1002/2017JA024931},
journal = {Journal of Geophysical Research. Space Physics},
number = ,
volume = ,
place = {United States},
year = {Fri Mar 30 00:00:00 EDT 2018},
month = {Fri Mar 30 00:00:00 EDT 2018}
}

Journal Article:
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