Enhanced collective stopping and drift of electron beams in fusion plasmas with heavy-ion species.

The transport and energy deposition of relativistic electron beams in transversely nonuniform plasmas are investigated with two-dimensional electromagnetic particle-in-cell simulations. For the beam with radius much larger than plasma skin depth, the current filamentation instability excited by the electron beam can be observed, which breaks the beam into filaments and leads to the formation of strong magnetic fields consequently. The effects of plasma ion species are significant and asymmetric transverse magnetic fields are formed in plasmas with heavy-ion species due to the asymmetric neutralization of beam space charge by plasma ions. The asymmetric transverse magnetic fields contribute to the directional drift of beam electrons to lower plasma density regions, which may accelerate the filaments merger process and lead to highly localized beam-energy deposition in plasmas.