Scaling laws for electromagnetic, pulsed plasma thrusters

The scaling laws of pulsed plasma thrusters operating in the predominantly electromagnetic acceleration mode (EM-PPT) are investigated theoretically a nd experimentally using gas-fed pulsed plasma thrusters. A fundamental char acteristic velocity that depends on the inductance per unit length and the square root of the capacitance to the initial inductance ratio is identifie d. An analytical model of the discharge current predicts scaling laws in wh ich the propulsive efficiency is proportional to the EM-PPT performance sca ling number, defined here as the ratio of the exhaust velocity to the EM-PP T characteristic velocity. The importance of the effective plasma resistanc e in improving the propulsive performance is shown. To test the validity of the predicted scaling relations, the performance of two gas-fed pulsed pla sma thruster designs (one with coaxial electrodes and the other with parall el-plate electrodes), was measured under 70 different operating conditions using an argon plasma. The measurements demonstrate that the impulse bit sc ales linearly with the integral of the square of the discharge current as e xpected for an electromagnetic accelerator. The measured performance scalin g is shown to be in good agreement with the theoretically predicted scaling . Normalizing the exhaust velocity and the impulse-to-energy ratio by the E M-PPT characteristic velocity collapses almost all the measured data onto s ingle curves that uphold the general validity of these scaling laws.