Role of the plasma magnetic filament in producing single-lobe gamma-ray emission

Establish whether the quasi-static azimuthal plasma magnetic field (magnetic filament) generated during relativistically induced transparency is the causal mechanism responsible for producing the single-lobed angular distribution of emitted gamma-rays observed in the particle-in-cell simulation with initial electron density n_e,0 = 1 n_cr. Specifically, determine if and how the magnetic filament dominates photon emission to yield a single-peaked profile despite a two-lobed electron angular distribution.

Background

The paper investigates why laser-driven gamma-ray emission can exhibit either double-lobed or single-lobed angular distributions, focusing on how direct laser acceleration (DLA) efficiency shapes these profiles. Using limiting-case analyses, the authors show that an electron moving along a plasma magnetic filament emits with a single peak, while a free electron in a plane electromagnetic wave emits with two peaks.

In particle-in-cell simulations, lowering the target density to n_e,0 = 1 n_cr yields a single-lobed emission pattern aligned with the laser direction, whereas a higher density (4 n_cr) yields a double-lobed pattern. The authors infer that efficient DLA is associated with emission dominated by the quasi-static azimuthal magnetic field (the filament), suggesting a central role for this structure.

At the end of the limiting-case section, the authors explicitly formulate a conjecture that the magnetic filament is crucial for establishing the single-lobe emission profile seen in the lower-density simulation. Confirming this conjecture would clarify the physical mechanism governing angular distributions in efficient DLA regimes.