Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Solar Particle Acceleration at Reconnecting 3D Null Points   Context: The strong electric fields associated with magnetic reconnection in
solar flares are a plausible mechanism to accelerate populations of high
energy, non-thermal particles. One such reconnection scenario occurs at a 3D
magnetic null point, where global plasma flows give rise to strong currents in
the spine axis or fan plane. Aims: To understand the mechanism of charged
particle energy gain in both the external drift region and the diffusion region
associated with 3D magnetic reconnection. In doing so we evaluate the
efficiency of resistive spine and fan models for particle acceleration, and
find possible observables for each. Method: We use a full orbit test particle
approach to study proton trajectories within electromagnetic fields that are
exact solutions to the steady and incompressible magnetohydrodynamic equations.
We study single particle trajectories and find energy spectra from many
particle simulations. The scaling properties of the accelerated particles with
respect to field and plasma parameters is investigated. Results: For fan
reconnection, strong non-uniform electric drift streamlines can accelerate the
bulk of the test particles. The highest energy gain is for particles that enter
the current sheet, where an increasing "guide field" stabilises particles
against ejection. The energy is only limited by the total electric potential
energy difference across the fan current sheet. The spine model has both slow
external electric drift speed and weak energy gain for particles reaching the
current sheet. Conclusions: The electromagnetic fields of fan reconnection can
accelerate protons to the high energies observed in solar flares, gaining up to
0.1 GeV for anomalous values of resistivity. However, the spine model, which
gave a harder energy spectrum in the ideal case, is not an efficient
accelerator after pressure constraints in the resistive model are included.

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The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: solv-int