Voltage-current characteristics of self-field magnetoplasmadynamic thrusters: modeling and application to lithium propellant

A non-dimensional voltage-current (V–J) model for self-field magnetoplasmadynamic thrusters (SF-MPDTs) is developed and compared to experimental data from a lithium-fed 30 kW-class thruster. Starting from first principles and incorporating physical scaling for thrust and dissipative sinks, the model yields a closed-form expression for the non-dimensional voltage as a function of the MPDT electromagnetic scaling number, $$\\xi = J/J_{ci}$$ , where $$J_{ci}$$ is the critical ionization current. The model accounts for ionization, thermal, and electrode losses, and predicts a universal $$\\widehat{V}(\\xi)$$ relationship valid across operating regimes with no free parameters. Validation using experimental data in the $$\\xi \\leq 1$$ regime demonstrates agreement down to $$\\xi \\simeq 0.25$$ . This universal model enables predictive scaling of SF-MPDT performance and provides a foundation for future analytical and experimental studies, including forthcoming higher-power lithium MPDT testing.