Schematic demonstrating the generation of the magnetic trap geometry. This schematic shows how the CME–CME or CME–background field interaction can generate collapsing magnetic trap geometries likely to generate the moving bursts studied here (after Magdalenić et al. 2002). When the CME-driven shock wave intersects an open field line twice, these intersections form two mirror points as the CME front advances in the direction indicated by v_CME/shock. At the mirror points, electrons (e⁻) can bounce back and forth until they escape. Once the electrons escape they can produce forward drift (FD) and reverse drift (RD) radio bursts. This can arise via a wavy shock front intersecting radial open fields (panel b) or a planar shock front intersecting helical open field lines (panel c).