MHD Power Generation with Photoionization

The recent development of an efficient source of focussed, continuous visible and ultraviolet light has aroused interest in photoionization as a means of enhancing the conductivity in MHD channels. This process has been examined for applications in space MHD generators employing Brayton and Rankine cycles. It was evaluated with respect to some other methods of ionization including magnetically induced non-equilibrium ionization, R. F. ionization, electron beam ionization, and the Penning effect where it is applicable. For non-condensing systems the working fluids. considered were He, Ne, and A. For condensing cycles, the fluids were K, Na, Zn, and Li vapors. Small percentages of cesium vapor were added to the working fluids in order to provide seeding. The results indicate that for some cases of practical interest photoionization may be competitive or more efficient than the other methods. Efficiency of ionization was defined as (Pg - Pi)/Pg, where Pg is the MHD power density generated and Pi the power density required by the light source to produce the desired ionization. Pg was assumed to be 107 watts/m3. Details for an example of an MED space power generating system using this type of ionization will be presented.