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The development and results of tests of 3 different arc configurations are presented. A doublering electrode arc unit, when discharging into the atmosphere, provided 40% utilization of theAVAILABLE ELECTRICAL POWER. This ac arc head was subsequently operated in conjunction with the previously constructed vac um system to establish subatmospheric test conditions in the plasma stream. It was found that this arc configurationvacuum system combination resulted in reduced thermal efficiencies. (Author)

The operation of an xisting subatmospheric plasma arc facility was characterized to assist the user in selecting the proper simulation conditions for materials test application. Eight principal test conditions were established within the operating limits of the arc, and the pertinent parameters describing the thermal environment were determined and tabulated. Subsequently, the hypersonic re-entry conditions corresponding to the thermal environment of the test conditions were computed and plotted on a velocity-altitude chart. In addition, an arc unit with water-cooled, non-consumable electrodes was developed to reduce contamination of the arc plasma. This arc, having double-ring electrode configuration, will generate plasma with a net average enthalpy of 8000 Btu/lb. The final phase concerned testing various materials under different exposure conditions. (Author)