Fig. 4: Trap-and-release flow mechanism at the magnetron head.

a General schematic of the magnetron head: orange lines represent the main Ar stream. Detail of the Ar⁺ ion impact (red arrows) toward the graphite target and the possible trajectory of knock out C atoms ejected toward the attraction areas (blue arrow), where gas-phase C–C coupling occurs to form C-NPs (blue spheres) and alkane chains (not at scale). b, c Torodial sectional streamlines ( b) and the stable manifold of the saddle point (c) in the region close to the graphite target. Trap-and-release events for C atoms released in the flow are shown by red streamlines. d Residence-time distribution as a function of azimuth along the injection ring. This distribution is computed for fluid trajectories originating from a circular ring of initial conditions with a uniform grid spacing along the azimuthal and radial directions, respectively.