Mass-dependent effects in ion conic production: The role of parallel electric fields

Previous observational studies indicate that the energies of different ion species in ion conics produced by broad-band extremely low frequency (BBELF ) waves are nearly equal. In contrast, theoretical studies predict a defini te preferential acceleration for heavy ions over lighter ions. We show that this discrepancy can be resolved if a downward parallel electric field is present in the heating region: for a sufficiently strong electric field ion s of different masses acquire approximately the same energy in escaping the trapping region.