Energy balance and efficiency of the pulsed plasma thruster

Abstract

The overall, thruster, and accelerator efficiencies of the pulsed plasma thruster (PPT) are defined in terms of the product of power processing unit, transfer, sheath, heat loss and frozen flow efficiencies. The exhaust kinetic energy of the PPT is evaluated by the introduction of a Maxwellian distribution for the flow velocity, corresponding to available specific impulse, velocity and ionization data from the LES-6 thruster. The Maxwellian is proposed as appropriate for a PPT exhaust in which a Saha-type ionization process is driven by an electron temperature small compared to the ionization potentials, and where the bulk of the low velocity particles is weakly accelerated to very small velocities compared to the average. The transfer, sheath, heat loss and frozen flow efficiencies are estimated using available data for the LES6 PPT, permitting energy estimates for each stage in the acceleration process. One of the predictions is that the ions, constituting 10% of the mass, carry nearly 50% of the kinetic energy and about 25% of the impulse bit. An estimate is made of the maximum possible efficiency for rectangular and coaxial PPT's.