Abstract: A high power non-transferred electric arc heater utilizing interelectrode segments which create a stepped arc chamber intermediate two hollow, substantially cylindrical, axially spaced electrodes. Gas to be heated is admitted upstream of the arc chamber and between adjacent segments. Gas is used to form a cold boundary layer about the expanding core of arc-heater gas. Additional secondary gas inlets adjacent the electrode provide fluid dynamic means for arc positioning on the electrode segments. Gas pressures of less than or in the range of about 1 atmosphere to about 50 atmospheres are used with power levels of about 10 MW being possible. The stepped arc chamber facilitates arc transfer to the downstream electrodes and allows a larger diameter for the arc heated gas while the boundary layer of gas maintaining comparable spacing along the length of the arc-heated gas and the surface of the arc chamber reducing the rate of heat transfer from the arc heated gas to the segments of the arc heater.