Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Space Science

Committee Chair

Jakobus le Roux

Committee Member

Haihong Che

Committee Member

Qiang Hu

Committee Member

Lingling Zhao

Committee Member

Lan Jian


Heliosphere (Astrophysics), Particle acceleration--Mathematical models, Space plasmas, Magnetic flux


Interplanetary coronal mass ejections (ICMEs) are major drivers of space weather in the inner heliosphere (which can negatively affect our spacecraft, astronauts, etc.). Traditionally, the scientific community has sought to explain energetic particle acceleration near ICME-driven shocks by invoking diffusive shock acceleration (DSA), which has been well studied. However, recent studies suggest that processes related to magnetic reconnection behind ICME-driven shocks can explain observed flux enhancements that contradict predictions by standard steady state DSA theory. In the previous decade, a combination of DSA at and acceleration by dynamic small-scale flux-ropes (SMFRs) downstream of the shock has been introduced to explain these anomalous flux enhancements. In spite of these recent advances, the study of particle acceleration by SMFRs is relatively new and thus the dominant mechanism through which particles are accelerated by SMFRs is not yet known. Previous in-situ studies of SMFR acceleration of energetic particles in the large-scale solar wind have been limited to acceleration events observed with single spacecraft at or beyond 1 AU, so a new search was conducted using Helios A data with the goal of identifying the first SMFR acceleration event within 1 AU. Two new SMFR acceleration events were revealed by this search. These events were modeled using two complementary approaches: (1) an analytical solution to a Parker transport equation, and (2) a numerical solution to a focused transport equation. The modeling efforts determined that, for the given events: (1) the SMFR acceleration mechanism associated with particle interaction with the component of the SMFR motional electric field parallel to the guide magnetic field dominates particle energy gain in both first and second order Fermi terms for low energies, (2) at higher energies the shear flow and compression acceleration mechanisms compete to accelerate particles, (3) particle escape from the SMFR acceleration plays a key role in reproducing observed spectral slopes, (4) particle energization rates decay at rates of r -1.5 (r refers to the heliocentric radial distance of the observations) or greater for second order Fermi processes, and (5) the Parker assumption (pitch-angle independent distribution function) may not be applicable to all SMFR acceleration events.



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