Plasma turbulence generated during particle acceleration in reconnection current sheets with magnetic islands

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To investigate turbulence generated inside RCSs with magnetic islands, let us re-145 produce a 3D RCS model and explore the dynamics of particles accelerated during their 146 passage through this magnetic field topology. We used the models described in our pre-  duced electric and magnetic fields in 3D RCSs with a single or multiple X-nullpoints (mag-152 netic islands). This approach allowed us to separate the original magnetic field config-153 uration of the reconnection from that induced by the plasma feedback due to the accel-154 erated particles and to discover triggers of plasma turbulence inside these complex mag-155 netic configurations.

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In the current paper, we do not separate the original and induced electromagnetic region to a larger domain comparing to the previous 2.5D studies by Muñoz and Büchner 160 (2016). The simulations start with a Harris-type current sheet (CS) in the x−z plane: where d cs is the half thickness of RCS. The B 0y is the initial guiding field, which is per-162 pendicular to the reconnection plane. In the presented simulation b g = B 0y /B 0z = 1.0.

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The initial density variation across the CS is: We chose a mass ratio m i /m e = 100, a temperature ratio T i /T e = 5, a background to the midplane, due to the presence of the strong guiding field.

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The reconnection process is still weakly affected by the kink instability at a larger 185 time, as evidenced in the isosurface of the electron energy distribution in Figure. (2a).

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The distributions are similar in the different x−z planes along the y−direction. If the 187 guiding field is weak, the flux ropes would be strongly interrupted. For example, we ob-  island reaches ∼ 36d i after t = 32Ω −1 ci in Figure. 1(g, h). It thus allows us to study In Figure. (3), the power spectrum of electric (magnetic) fields of the whole box 201 are measured at t = 32Ω −1 ci as |E| 2 (k) (|B| 2 (k)) in the Fourier space, where k stands 202 for the wavenumber in the reconnection plane. In this session, we did not discuss the anisotropic   Then as the inspecting plane moves deeper into the magnetic island, the pertur-231 bation in the ion phase space was found at z = 10 (or∆z ∼ 12 away from the X-nullpoint) 232 in Figure 4(b), where the arcs in the x = 0 to 2 region represent different groups of ion 233 beams. We did not find any clear ion holes in the phase space, but those arcs disappear 234 quickly further in the downstream, which suggest the ion beams are also suppressed by 235 plasma turbulence.  which is a powerful tool to analyse time-series data collected by a pinpoint in the do-242 main, to study the fluctuations using discrete wavelet transform (Farge, 1992). 243 We explored the fluctuations of electric and magnetic fields in the exhaust obtained

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In the very-high-frequency part (≥ ω pe ), we first noticed that the perpendicular 279 electric field E ⊥ at f > ω pe is damped significantly as it moves away from the X-nullpoint.

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In other words, these waves represented by E ⊥ are only observable near X-nullpoints.  In the sub-high-frequency region, Ω ce < f < ω pe , we found several distinct spikes in 285 all the fields at three locations. Considering that the periodic boundary condition along 286 z−axis stands for simulating a chain of magnetic islands, it suggests that the magnetic 287 island pool is fulfilled with these electromagnetic fluctuations above Ω ce . Besides, we also 288 noticed that the enhancement near f ≈ ω lh , f < Ω ce , and Ω ce < f < ω pe are consis-289 tent with the dark horizontal stripes in the wavelet power spectrum in Figure.

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The frequency spectra of electric and magnetic fields obtained at different locations 364 also revealed that turbulence was changing in the outflow from the X-nullpoint to O-nullpoint.