Operation of the MPD thruster with stepped current input
A magnetoplasmadynamic (MPD) thruster was operated with stepped current pulses in order to investigate the sensitivity of its operation to non-constant current input. The thruster terminal voltage is found to lag the current increment by increasing times as the highest level of the stepped current pulse nears the onset condition. Magnetic field transients corresponding to the terminal voltage transients appear in the thruster exhaust. The magnetic field and terminal voltage equilibrations can be interpreted in terms of magnetic diffusion and convection processes. The time constants of equilibration are largest in the exhaust portion of the discharge, where the discharge scale length is much larger than in the thrust chamber. The transient thrust following a current step up is estimated to be below the quasi steady thrust, while the transient thrust following a current step down is estimated to be above the quasi steady thrust. When the thruster is powered with a current step up whose upper plateau is near the onset conditions, the prolonged discharge transient allows a diagnostic look at the development on the onset condition. Electric field probing for different propellant injection geometries suggest that the larger terminal voltages associated with operation near onset may result from two distinct processes: an increasing anode fall, probably caused by insufficient propellant near the anode, or the back emf of the plasma flow.
- Research Organization:
- Princeton Univ., NJ (USA)
- OSTI ID:
- 6076375
- Country of Publication:
- United States
- Language:
- English
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