A characteristic velocity for gas-fed PPT performance scaling

The performance scaling of gas-fed pulsed plasma thrusters (GPPPTs) is investigated theoretically and experimentally. A characteristic velocity for GFPPTs that depends on the inductance-per-unit-length and the square root of the capacitance to initial inductance ratio has been identified. An analytical model of the discharge current predicts the efficiency to be proportional to the GFPPT performance scaling number, defined here as the ratio of the exhaust velocity to the GFPPT characteristic velocity. To test the validity of the predicted scaling relations, the performance of two rapid-pulse-rate GFPPT designs, PT5 (coaxial electrodes) and PT9 (parallel-plate electrodes), has been measured over 70 different operating conditions with argon propellant. The measurements demonstrate that the impulse bit scales linearly with the integral of the discharge current squared as expected for an electromagnetic accelerator. The measured performance scaling in both electrode geometries is shown to be in good agreement with theoretical predictions using the performance scaling number. Normalizing the exhaust velocity and the impulse-to-energy ratio by the GFPPT characteristic velocity collapses almost all the measured data onto single curves that represent the scaling relations for these GFPPTs.