On the potential for direct or MHD conversion of power from a novel plasma source to electricity for microdistributed power applications

The generation of electricity using direct electrostatic and magnetohydrodynamic (MHD) conversion of the plasma-particle energy of small to midsize chemically assisted microwave or glow discharge plasma (CA-plasma) power sources in the range of a few hundred Watts to several tens of kilowatts for microdistributed commercial applications (e.g., household, automotive, light industry, and space-based power) is studied for the first time. In the determination of the effect of plasma parameters on conversion efficiency, careful attention was paid to the unique plasma conditions of low-pressure, low-ionization fraction, and nonthermal ion energies that are much greater than that of the thermal ions of traditional MHD but much lower than those of a fully ionized plasma typically generated for fusion experiments. The density of plasma ions and neutrals and their cross sections for processes such as charge exchange were also considered. The most important parameters were found to be charged-particle density and energy, as well as the large inventory of neutral gas atoms and molecules. Momentum and charge exchange of plasma ions with the large background fraction of neutrals represents a limitation to conversion efficiency. Two conversion technologies were examined in some detail. We considered the possibility of converting a CA-plasma using adaptations of a member of the broad category of electromagnetic direct converters previously developed for recovery and conversion of the high energy particles lost from tandem mirror and magnetically confined plasmas, and an MHD converter previously developed for conversion of high pressure combustion gases to electricity. While it was found that both conversion techniques performed well under ideal conditions for conversion of plasma to electricity showing conversion efficiencies of >50%, the tight coupling of plasma cell and converter, size limitations, particle energy, and the substantial inventory of relatively low energy neutrals may substantially reduce the efficacy of direct electrostatic converters under these conditions. However, MHD conversion of CA-plasmas appears feasible at /spl sim/50% efficiency with a simple compact design.