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

Establish whether the quasi-static azimuthal plasma magnetic filament generated by laser-driven electron currents is the crucial mechanism responsible for the single-lobed angular distribution of emitted gamma-rays observed in the 3D particle-in-cell simulation with target electron density n_e0 = 1 n_cr, by determining if the filament-driven field, rather than the laser field, governs the emission profile in that regime.

Background

The paper analyzes photon emission patterns from laser-irradiated plasmas using both 3D PIC simulations and test-electron models. It contrasts two limiting cases: an electron interacting solely with the laser field, which yields a double-peaked emission profile, and an electron guided by an azimuthal plasma magnetic filament, which yields a single-peaked emission profile.

In 3D PIC simulations, reducing the target density to n_e0 = 1 n_cr resulted in a transition from a conventional double-lobed emission to a single-lobed, strongly collimated profile. The authors infer that the plasma magnetic filament can dominate the emission process in efficient direct laser acceleration conditions, potentially explaining the single-lobed profile.

Based on these observations, the authors explicitly conjecture that the magnetic filament plays a crucial role in establishing the single-lobe emission profile in the lower-density target case, motivating a precise determination of this causal mechanism.