arXiv subjects

Nishant Narechania

Publications and source records attributed to Nishant Narechania.

4 recordsLinked to original sources

arXiv2026

Geometric numerical discretization of electromagnetic quasineutral models

In this work, the geometric electromagnetic Particle-in-Cell (PIC) framework, GEMPICX, is extended to solve the quasineutral, fully kinetic Vlasov-Maxwell equations on dual grids using mimetic finite differences. The discrete action principle is derived, taking into account the duality between the grids. The temporal derivative of the electric field does not directly appear in the dynamical system for the quasineutral model. Hence, a discretized curl-curl equation is used to implicitly obtain the electric field at every time-step. This also circumvents the need to obtain electric potentials. A Lagrange multiplier is used to maintain the discretized divergence of the current density at machine zero.

physics.plasm-ph↗

arXiv2026

Geometric numerical discretization of a quasineutral hybrid model of drift-kinetic electrons and fully kinetic ions

We extend the geometric electromagnetic particle-in-cell (PIC) framework, GEMPICX, to solve the quasineutral hybrid Vlasov-Maxwell equations with drift-kinetic electrons and fully kinetic ions. A structure-preserving finite difference method that employs dual grids is used. The discrete action principle for the hybrid model is derived, using the dual nature of the grids. The dynamical system for this hybrid quasineutral model does not explicitly involve the temporal evolution term for the electric field. A curl-curl equation is therefore used to implicitly obtain the component of the electric field that is parallel to the background magnetic field, at every timestep. The perpendicular component of the electric field is obtained using the quasineutral Ampere's equation without the displacement current, combined with the definition of the current in the drift-kinetic model. The discretized versions of the electric field equations are large, sparse linear systems. A fully explicit time-stepping scheme as well as two implicit-explicit (IMEX) schemes are tested. The numerical model is validated by verifying the various waves obtained from the dispersion relation.

physics.plasm-ph↗

arXiv2026

A quasi-neutral electromagnetic hybrid model with drift-kinetic electrons and fully kinetic ions

In this work, we propose a hybrid model that combines drift-kinetic electrons with fully kinetic ions under the quasi-neutrality assumption, discretized using a geometric particle-in-cell framework on dual-grids. The model advances the perturbed electromagnetic fields $E$ and $B$ directly, rather than the scalar and vector potentials. The parallel electric field $E_\parallel$ is obtained from Ohm's law. The perpendicular electric field $E_\perp$ is computed from Ampère's law by extracting the $E_\perp$-dependent component of the drift-kinetic electron current. The quasi-neutrality constraint eliminates high-frequency light waves and Langmuir waves from the system. Temporal discretization is performed using low-storage Runge--Kutta schemes. In this quasi-neutral hybrid model, the right-hand polarized wave branch exhibits a whistler-like dispersion relation, which imposes a stringent timestep constraint. To address this, we develop a novel implicit-explicit splitting scheme for Faraday's law that significantly relaxes the timestep stability restriction. The model is validated in slab geometry by reproducing cold plasma wave branches, ion Bernstein waves, compressional and shear Alfvén waves, and ion acoustic waves.

physics.plasm-ph↗

arXiv2025

Radiation-magnetohydrodynamics with MPI-AMRVAC using flux-limited diffusion

Context. Radiation plays a significant role in solar and astrophysical environments as it may constitute a sizeable fraction of the energy density, momentum flux, and the total pressure. Modelling the dynamic interaction between radiation and magnetized plasmas in such environments is an intricate and computationally costly task. Aims. The goal of this work is to demonstrate the capabilities of the open-source parallel, block-adaptive computational framework MPI-AMRVAC, in solving equations of radiation-magnetohydrodynamics (RMHD), and to present benchmark test cases relevant for radiation-dominated magnetized plasmas. Methods. The existing magnetohydrodynamics (MHD) and flux-limited diffusion (FLD) radiative-hydrodynamics physics modules are combined to solve the equations of radiation-magnetohydrodynamics (RMHD) on block-adaptive finite volume Cartesian meshes in any dimensionality. Results. We introduce and validate several benchmark test cases such as steady radiative MHD shocks, radiation-damped linear MHD waves, radiation-modified Riemann problems and a multi-dimensional radiative magnetoconvection case. We recall the basic governing Rankine-Hugoniot relations for shocks and the dispersion relation for linear MHD waves in the presence of optically thick radiation fields where the diffusion limit is reached. The RMHD system allows for 8 linear wave types, where the classical 7-wave MHD picture (entropy and three wave pairs for slow, Alfven and fast) is augmented with a radiative diffusion mode. Conclusions. The MPI-AMRVAC code now has the capability to perform multidimensional RMHD simulations with mesh adaptation making it well-suited for larger scientific applications to study magnetized matter-radiation interactions in solar and stellar interiors and atmospheres.

astro-ph.SR↗