arXiv subjects

N Bisai

Publications and source records attributed to N Bisai.

3 recordsLinked to original sources

arXiv2026

Electromagnetic filament coalescence as magnetic island merging with diamagnetic effects

We investigate the nonlinear coalescence of two current-carrying ELM filaments using a three-dimensional electromagnetic fluid model. In the flat-density limit, the coalescence exhibits magnetic island-like reconnection, characterized by X-point formation, current-sheet development, and Sweet-Parker-like resistive scaling. Introducing a blob-like density perturbation modifies the reconnection dynamics: while the peak reconnection rate remains nearly unchanged for weak perturbations, it decreases and is increasingly delayed for larger density amplitudes. Analysis of the induction equation reveals a transition from resistive to increasingly density-dependent advective dynamics. Finite density perturbations also enhance the post-compression rebound, or sloshing, of the filaments. The sloshing amplitude increases with the density-gradient pressure force, establishing density perturbation as an additional control parameter for both reconnection and filament sloshing. These results highlight the coupled electromagnetic and pressure-driven dynamics governing the nonlinear evolution of ELM filaments in the tokamak edge.

physics.plasm-ph↗

arXiv2026

Nonlinear Dynamics of Current-Carrying ELM Filaments: Spiral Vorticity, Rotation, and Velocity Suppression

In this work, we investigate the nonlinear dynamics of isolated current-carrying edge-localized mode (ELM) filaments using a reduced electromagnetic fluid model in slab geometry. Numerical simulations show that unidirectional parallel current significantly suppresses radial filament velocity and reduces the outward propagation velocity by weakening the curvature-driven interchange force. The reduction in radial velocity is found to follow a modified scaling relation, demonstrating that increasing current progressively weakens outward filament propagation. Analysis of the vorticity equation shows that the electromagnetic current source changes from a dipolar structure to a remarkable spiral pattern, and overcomes the conventional curvature drive in the nonlinear phase. This current-driven source directly imprints its topology on the vorticity field, resulting in spiral vorticity, enhanced angular momentum, increased rotational energy, and localized shear layers. The filament therefore undergoes a transition from a conventional propagating state to a rotationally self-organized electromagnetic structure. These findings demonstrate that parallel current acts as an effective electromagnetic vorticity source and provides new insight into the nonlinear dynamics of ELM filaments in tokamak edge plasmas.

physics.plasm-ph↗

arXiv2024

Merging dynamics of plasma blobs in the Scrape-off Layer of a tokamak

The emergence and merging of high-density coherent structures - plasma blobs - is a recurrent phenomenon in the Scrape-off layer (SOL) of a tokamak plasma that has a significant impact on the rate of convective transport in that region. We report on a model study of the merging of two electromagnetically interacting blobs in a high beta plasma. Our detailed numerical simulations show that the merging process is akin to the coalescence instability between two magnetic islands but with important differences due to the density perturbation. The blobs are found to rotate about each other during merging and the merging occurs with an acceleration in the poloidal direction that is directly proportional to the square of the current density of the blobs and inversely proportional to its density. The separation distance between two high current density blobs is also seen to oscillate indicating a sloshing behavior.

physics.plasm-ph↗