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Michael Harrison Thomas Neukirch Michael Hesse 5 th Cambridge Workshop on Magnetic Reconnection Bad Honnef August 17-22, 2008. A Comparison of 2D PIC simulations of Reconnection. Motivation.

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Michael Harrison

Thomas Neukirch

Michael Hesse

5th Cambridge Workshop on Magnetic Reconnection

Bad Honnef

August 17-22, 2008

A Comparison of 2D PIC simulations of Reconnection


Motivation
Motivation

  • To compare the reconnection process using 2.5D PIC simulations starting from different initial conditions.

  • To investigate the morphology of the off-diagonal components of the electron pressure tensor as you go from weak to strong guide field using 2.5D PIC simulations to compare to previous results.

  • To investigate this transition using Vlasov-Maxwell equilibria resulting from distribution functions that extend beyond the Harris sheet.

  • To include in the investigation a comparison to the reconnection process starting from a self-consistent force-free Vlasov-Maxwell equilibria.

  • Currently we carry out our simulations with mass ratio = 1


The structure of the diffusion region
The Structure of the Diffusion Region

  • The electron equation of motion

  • The y component of the electric field can be written as

  • Is found that the gradients of the off-diagonal terms of the pressure tensor are the dominant contributions to at the X-Point (Hesse 1999, 2001, Pritchett 2001, etc.).


Harris sheet cases
Harris Sheet Cases

Flux Normalised Reconnection Rate

Reconnected Flux

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Pressure tensor component comparisons
Pressure Tensor Component Comparisons

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Pressure tensor component comparisons1
Pressure Tensor Component Comparisons

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Anisotropic bi maxwellian distribution function
Anisotropic Bi-Maxwellian Distribution Function

  • Have to find periodic solutions of the differential equations.

  • The case gives anti-parallel field configuration –

  • The case gives linear force-free equilibrium (Bobrova et al. 2001)

  • Can use the parameter to vary the shear field while keeping constant

  • Can investigate the transition from a pressure balanced equilibrium to a force-free equilibrium.


The two cases
The Two Cases

Numerical Solution


Anisotropic bi maxwellian cases
Anisotropic Bi-Maxwellian Cases

Flux Normalised Reconnection Rate

Reconnected Flux

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Pressure Tensor Component Comparisons

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Force-Free

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Pressure tensor component comparisons2
Pressure Tensor Component Comparisons

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Force-Free

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Conclusions
Conclusions

  • We have investigated the morphology of the off-diagonal components of the electron pressure tensor as you make the transition from an initial condition with a weak guide field through to a strong guide field including a linear force-free initial configuration.

  • In the initial stages of reconnection the structure of the electron pressure tensor components are similar for all initial conditions when compared to the previously known Harris sheet cases.

  • It can be seen that in the case of the periodic equilibria resulting from an anisotropic bi-Maxwellian distribution function the structure of the electron pressure tensor components are drastically changed in the latter stages due to interaction of the multiple current sheets.

  • The evolution of the periodic equilibria results in an almost complete change in the geometry of the field from initially having a structure to having a structure at the end.


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