Focusing resonance cones

The potential for an oscillating ring source immersed in cold, magnetized, collisionless plasma in the resonance cone regime (K_∥/K_⊥< 0 ) is evaluated exactly and asymptotically, giving insight into the gross spatial behavior of the focusing resonance cones. The nature of the singularity in potential is clarified by the introduction of a noninfinitesimal collision frequency. Thermal effects are considered numerically, revealing an interesting interference structure in potential as well as a density depression near the focus of the cone due to the ponderomotive force.