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Particle acceleration at a reconnecting magnetic separator  

Thomas Neukirch   Submitted: 2014-11-20 01:52

While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. The effect upon particle behaviour of initial position, pitch angle and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains several free parameters and we study the effect of changing these parameters upon particle acceleration, in particular in view of the final particle energy ranges which agree with observed energy spectra.

Authors: Threlfall, J., Neukirch, T., Parnell, C. E., Eradat Oskoui, S.
Projects: None

Publication Status: A&A (in press)
Last Modified: 2014-11-20 07:41
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A detailed investigation of the properties of a Vlasov-Maxwell equilibrium for the force-free Harris sheet}  

Thomas Neukirch   Submitted: 2009-10-31 08:13

A detailed discussion is presented of the Vlasov-Maxwell equilibrium for the force-free Harris sheet recently found by Harrison and Neukirch (Phys. Rev. Lett. 102, 135003, 2009). The derivation of the distribution function and a discussion of its general properties and their dependence on the distribution function parameters will be given. In particular, the distribution function can be single-peaked or multi-peaked in two of the velocity components, with possible implications for stability. The dependence of the shape of the distribution function on the values of its parameters will be investigated and the relation to macroscopic quantities such as the current sheet thickness will be discussed.

Authors: Thomas Neukirch, Fiona Wilson and Michael G. Harrison
Projects: None

Publication Status: accepted for publication by Physics of Plasmas
Last Modified: 2009-11-01 07:42
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On the Relationship between Equilibrium Bifurcations and Ideal MHD Instabilities for Line-Tied Coronal Loops}  

Thomas Neukirch   Submitted: 2009-10-30 09:12

For axisymmetric models for coronal loops the relationship between the bifurcation points of magnetohydrodynamic (MHD) equilibrium sequences and the points of linear ideal MHD instability is investigated imposing line-tied boundary conditions. Using a well-studied example based on the Gold-Hoyle equilibrium, it is demonstrated that if the equilibrium sequence is calculated using the Grad-Shafranov equation, the instability corresponds to the second bifurcation point and not the first bifurcation point because the equilibrium boundary conditions allow for modes which are excluded from the linear ideal stability analysis. This is shown by calculating the bifurcating equilibrium branches and comparing the spatial structure of the solutions close to the bifurcation point with the spatial structure of the unstable mode. If the equilibrium sequence is calculated using Euler potentials the first bifurcation point of the Grad-Shafranov case is not found, and the first bifurcation point of the Euler potential description coincides with the ideal instability threshold. An explanation of this results in terms of linear bifurcation theory is given and the implications for the use of MHD equilibrium bifurcations to explain eruptive phenomena is briefly discussed.

Authors: Neukirch, T., Romeou, Z.
Projects: None

Publication Status: Solar Physics, accepted
Last Modified: 2009-11-01 07:42
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Electron acceleration in reconnecting current sheets  

Thomas Neukirch   Submitted: 2004-09-23 07:35

We present the results of charged particle orbit calculations in prescribed electric and magnetic fields motivated by magnetic reconnection models. Due to the presence of a strong guide field the particle orbits can be calculated in the guiding centre approximation. The electromagnetic fields are chosen to resemble a reconnecting magnetic current sheet with a localised reconnection region. An initially Maxwellian distribution function in the inflow region can develop a beam-like component in the outflow region. Possible implications of these findings for acceleration scenarios in solar flares will be discussed.

Authors: Wood, P. and Neukirch, T.
Projects:

Publication Status: Solar Physics (accepted)
Last Modified: 2004-10-24 14:23
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Abstracts by Author
Particle acceleration at a reconnecting magnetic separator
A detailed investigation of the properties of a Vlasov-Maxwell equilibrium for the force-free Harris sheet}
On the Relationship between Equilibrium Bifurcations and Ideal MHD Instabilities for Line-Tied Coronal Loops}
Electron acceleration in reconnecting current sheets

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