Comparison of test particle acceleration in torsional spine and fan reconnection regimes

Abstract

Magnetic reconnection is a common phenomenon taking place in astrophysical and space plasmas, especially in solar flares which are rich sources of highly energetic particles. Torsional spine and fan reconnections are important mechanisms proposed for steady-state three-dimensional nullpoint reconnection. By using the magnetic and electric fields for these regimes, we numerically investigate the features of test particle acceleration in both regimes with input parameters for the solar corona. By comparison, torsional spine reconnection is found to be more efficient than torsional fan reconnection in an acceleration of a proton to a high kinetic energy. A proton can gain as high as 100 MeV of relativistic kinetic energy within only a few milliseconds. Moreover, in torsional spine reconnection, an accelerated particle can escape either along the spine axis or on the fan plane depending on its injection position. However, in torsional fan reconnection, the particle is only allowed to accelerate along the spine axis. In addition, in both regimes, the particle's trajectory and final kinetic energy depend on the injection position but adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory. V C 2014 AIP Publishing LLC. [http://dx.

Test particle acceleration in resistive torsional fan magnetic reconnection using laboratory plasma parameters

“…After this peak kinetic energy gain, the total energy of each particle is rapidly lost due to collisional effects ((2.16), black dotted lines) as the particles propagate away from the regions of strong electric potential. The shape of the initially rapid kinetic energy gains of the acceleration phases (red lines, figure 7c, f and figure 7d,g; ≈1300-1600 time steps) follow the behaviour found in similar particle energization simulations of both torsional fan and torsional spine reconnection (Dalla & Browning 2005Stanier et al 2012;Hosseinpour 2014aHosseinpour ,b, 2015Hosseinpour et al 2014;Gascoyne 2015). However, those simulations were rooted in the collisionless nature of solar coronal conditions, whereas here a more resistive plasma nature contributes strongly to total energy loss.…”

“…where distances are scaled to a characteristic length described in § § 2.2 and 3.2, j, l and c govern the degree and spatial extent of the twist, and β and γ are positive integers. Throughout this paper, we set j = 5, γ = 3, l = 1 and β = c = 0, corresponding to a generic radially linear perturbation, and consistent with the torsional fan reconnection simulations of Hosseinpour (2015), Hosseinpour (2014a) and Hosseinpour et al (2014). Using these values, (2.1) reduces to…”

“…The initial study of Chesny et al (2017) described a feasible apparatus that achieved both of the previous conditions, but stopped short of demonstrating particle response to reconnection. Numerous authors (Dalla & Browning 2005Stanier, Browning & Dalla 2012;Hosseinpour, Mehdizade & Mohammadi 2014;Gascoyne 2015;Threlfall et al 2015;Pallister, Pontin & Wyper 2019) have employed a test particle approach to demonstrate relativistic particle acceleration in torsional reconnection under collisionless solar plasma conditions. These studies were able to broadly confirm satellite observations of the acceleration of protons to ∼ 10 MeV levels and the formation of collimated, bidirectional jets.…”

Why Are Flare Ribbons Associated with the Spines of Magnetic Null Points Generically Elongated?

“…In such a configuration, the vicinity of the original null becomes highly turbulent, and one would expect efficient particle scattering along both the large-scale spine and fan directions. Second, if there is some large-scale rotational external motion, this can drive torsional spine reconnection, associated with a component of current parallel to the spine which can accelerate particles along the spine (Hosseinpour, Mehdizade, and Mohammadi, 2014). Finally, one could expect strong mirroring of particles close to the fan footpoints to lead to a distribution of particles also around the spine footpoints (note that the PIC simulations of Baumann, Haugbølle, and Nordlund (2013) did not cover the domain all the way to the photosphere).…”

Toward laboratory torsional spine magnetic reconnection

“…While their analysis was based on X-point plasma outflows of the order of the local v A that are possible in existing spheromak and tokamak-style laboratory configurations (Cazzola et al 2016), any practical, mass-constrained spacecraft application would require explicit control of a centimetre-scale highly compact plasma sheet concentrated along open magnetic field lines, such as that explored here, that can propagate far from the reconnection region. The TSR mode has been suggested to be a highly efficient mechanism for accelerating injected particles to spine-aligned relativistic velocities on fast ∼ms time scales (Hosseinpour 2014;Hosseinpour, Mehdizade & Mohammadi 2014). Issues of plasma confinement and losses present in other plasma propulsion systems could also be significantly decreased, as TSR mode charged particle acceleration is only efficient close to the rotational perturbation region (Hosseinpour 2014), e.g.…”