Three avenues for increasing the enthalpy attainable from scalable high performance arc heaters were studied: radiation loss reduction, magnetic control of arc terminations and geometry changes. The radiation loss work showed centerline arc column enthalpies over 30,000 Btu/lb. Because the arc column is optically thin, substantial reduction of radiation loss seems infeasible. Large arc devices will be limited more by radiation than small. Modest improvements in performance were achieved with magnetic interactions, which were found to be extremely complex. Proper proportioning of radial and axial field components was quite important, especially in maintaining scalability. Marked undesirable effects occurred when the auxiliary field coil was located near the electrode gap. Distinct performance improvements were achieved by changes in geometry, with air injection and chamber design the most significant for the low flow, high current region studied. (Author).