Extrathermal Electrical Conductivity Measurements in a Magnetoplasmadynamic Generator

Abstract

A DETAILED description of the International Research and Development Co., Ltd., magnetoplasmadynamic (MPD) generator has been given previously^1,2. On July 14, 1964, a series of power generation experiments with cæsium seeding of the helium were undertaken. This series differed from the previously reported runs³ mainly in the generator and nozzle configuration and materials. To reduce end current leakage, the tantalum nozzle used previously was replaced by a boron nitride nozzle, the exit region of the generator lengthened by 2 in. and the interior of the diffuser inlet spray-coated with alumina. The generator channel was constructed from boron nitride in attempts to reduce the internal current leakage encountered previously with alumina³. Sixteen pairs of narrow (1/16 in. × 1/2 in.) tantalum electrodes replaced the five pairs of square (1/2 in. × 1/2 in.) electrodes used previously; the gap between the electrodes was large (3/16 in.), to reduce insulator and boundary layer electrical breakdown. Five pairs of tantalum pins (1/16 in. diam.) were used to monitor open circuit voltages, two pairs in the nozzle and three pairs in the generator exit region. Four static pressure tappings and three thermocouples were also located in the channel wall. During operation of the loop nozzle inlet gas temperatures in excess of 1,700° C were measured. The maximum channel temperature measured was 1,110° C with a corresponding flow velocity of 1,730 m/sec and a Mach number of 0.79.