“…When the discharge current is less than 0.1 A, radio frequency (RF) cathodes with an emission current density on the order of 10 A/m 2 are used, particularly for ion neutralizers in ion engines. 2) Note that both hollow cathodes and RF cathodes require working gas, which is not fully accelerated and does not contribute to thrust generation. As a result, the total thrust performance (defined in Eqs.…”