25 research outputs found
In Search of a Data Driven Symbolic Multi-Fluid 10-Moment Model Closure
The inclusion of kinetic effects into fluid models has been a long standing
problem in magnetic reconnection and plasma physics. Generally the pressure
tensor is reduced to a scalar which is an approximation used to aid in the
modeling of large scale global systems such as the Earth's magnetosphere. This
unfortunately omits important kinetic physics which have been shown to play a
crucial role in collisionless regimes. The multi-fluid 10-moment model on the
other-hand retains the full symmetric pressure tensor. The 10-moment model is
constructed by taking moments of the Vlasov equation up to second order, and
includes the scalar density, the vector bulk-flow, and the symmetric pressure
tensor for a total of 10 separate components. Use of the multi-fluid 10-moment
model requires a closure which truncates the cascading system of equations.
Here we look to leverage data-driven methodologies to seek a closure which may
improve physical fidelity of the 10-moment multi-fluid model in collisionless
regimes. Specifically we use the Sparse Identification of Nonlinear Dynamics
(SINDy) method for symbolic equation discovery to seek the truncating closure
from fully kinetic particle-in-cell simulation data, which inherently retains
the relevant kinetic physics. We verify our method by reproducing the 10-moment
model from the PIC particle data and use the method to generate a closure
truncating the 10-moment model which is analyzed through the nonlinear phase of
reconnection
Global Ten-Moment Multifluid Simulations of the Solar Wind Interaction with Mercury: From the Planetary Conducting Core to the Dynamic Magnetosphere
For the first time, we explore the tightly coupled interior-magnetosphere
system of Mercury by employing a three-dimensional ten-moment multifluid model.
This novel fluid model incorporates the non-ideal effects including the Hall
effect, inertia, and tensorial pressures that are critical for collisionless
magnetic reconnection; therefore, it is particularly well suited for
investigating magnetic reconnection in Mercury's magnetotail
and at the planet's magnetopause. The model is able to reproduce the observed
magnetic field vectors, field-aligned currents, and cross-tail current sheet
asymmetry (beyond the MHD approach) and the simulation results are in good
agreement with spacecraft observations. We also study the magnetospheric
response of Mercury to a hypothetical extreme event with an enhanced solar wind
dynamic pressure, which demonstrates the significance of induction effects
resulting from the electromagnetically-coupled interior. More interestingly,
plasmoids (or flux ropes) are formed in Mercury's magnetotail during the event,
indicating the highly dynamic nature of Mercury's magnetosphere.Comment: Geophysical Research Letters, in press, 17 pages, 4 (fancy) figure
Discrete Kinetic Eigenmode Spectra of Electron Plasma Oscillations in Weakly Collisional Plasma: A Numerical Study
It has been demonstrated that in the presence of weak collisions, described by the Lenard-Bernstein collision operator, the Landau-damped solutions become true eigenmodes of the system and constitute a complete set. We present numerical results from an Eulerian Vlasov code that incorporates the Lenard-Bernstein collision operator. The effect of the collisions on the numerical recursion phenomenon seen in Vlasov codes is discussed. The code is benchmarked against exact linear eigenmode solutions in the presence of weak collisions, and a spectrum of Landau-damped solutions is determined within the limits of numerical resolution. Tests of the orthogonality and the completeness relation are presented
Energy transport during 3D small-scale reconnection driven by anisotropic plasma turbulence
Energy dissipation in collisionless plasmas is a longstanding fundamental
physics problem. Although it is well known that magnetic reconnection and
turbulence are coupled and transport energy from system-size scales to
sub-proton scales, the details of the energy distribution and energy
dissipation channels remain poorly understood. Especially, the energy transfer
and transport associated with three dimensional (3D) small-scale reconnection
that occurs as a consequence of a turbulent cascade is unknown. We use an
explicit fully kinetic particle-in-cell code to simulate 3D small scale
magnetic reconnection events forming in anisotropic and Alfv\'enic decaying
turbulence. We identify a highly dynamic and asymmetric reconnection event that
involves two reconnecting flux ropes. We use a two-fluid approach based on the
Boltzmann equation to study the spatial energy transfer associated with the
reconnection event and compare the power density terms in the two-fluid energy
equations with standard energy-based damping, heating and dissipation proxies.
Our findings suggest that the electron bulk flow transports thermal energy
density more efficiently than kinetic energy density. Moreover, in our
turbulent reconnection event, the energy-density transfer is dominated by
plasma compression. This is consistent with turbulent current sheets and
turbulent reconnection events, but not with laminar reconnection.Comment: Accepted for publication in Ap