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 definite preferential acceleration for heavy ions over lighter ions. We show that this discrepancy is resolved if a downward parallel electric field is present in the heating region: for a sufficiently strong electric field ions of different masses acquire approximately the same energy in escaping the trapping region.
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