Parallel electric fields

A steady state one-dimensional model is used to estimate the electron current along a field line from the auroral zone to the plasmasheet when a potential difference exists between its ends. The plasmas at either end, the ionosphere and the plasmasheet, are assumed thermal. When typical experimental values are substituted into the analytic expression obtained it is found that potential differences of the order of 10 kV are required to drive the field-aligned currents sometimes observed.