An Investigation of Magnetically Induced Ionization in Rare Gas Mixtures

The major objective of the research described in this paper was to determine whether an MHD generator could be operated in a non-equilibrium ionization mode without seeding the gas flow with a low ionization potential component (e.g. caesium). Elimination of the seed material would simplify the working fluid circulation loop and ease the channel wall materials problem. The approach followed was to seek a gas combination which possessed a low breakdown potential and a low mean atomic weight to ensure a large streaming velocity, resulting in high values of induced E/p for moderate magnetic fields and pressures. A mixture of helium and argon appeared to offer the desired properties and calculations were made to compare the conductivity of a helium-rich mixture with that of pure argon under the same operating conditions. The apparatus consisted of an MHD channel with segmented electrodes coupled to a plasma jet heater. Experiments were performed to measure the plasma conductivity as a function of magnetic field and external load resistance. The results indicate that limited magnetically induced ionization was achieved. (author)