A self-cycling fluid heater is described which includes a high temperature upstream preheater for elevating the stream temperature. A high intensity jet arc heater heats the preheated fluid stream to ultrahigh reaction temperatures and discharges the stream into an electric resistance tubular heat exchanger. The heat exchanger has variations in wall thickness at measured intervals along its length to control the temperature of the fluid passing through the heat exchanger for desired time intervals to provide the specified chemical reactions desired
