A correction to Whipple's law for ion-trap Current

We have analyzed a phenomenon heretofore ignored in the analyses of ion traps, which are used to determine ion temperature, among other plasma parameters, in planetary ionospheres: ions that are rejected by the trap perturb the plasma well ahead of the Debye sheath at the front of the trap.The determination of the perturbed plasma flow is found to depend on the fact that the ionospheric plasma be stable to quasineutral, ion-acoustic perturbations.