Abstract: A product stream of hot gas is formed at elevated pressure. A primary gas stream is passed at elevated pressure through a flow control valve in a primary gas stream inlet to a plasma generator. The plasma generator is operated so as to heat the primary gas stream. The heated primary gas stream passes into a gas mixing chamber. A secondary gas stream passes through a flow control valve into the gas mixing chamber. A product gas stream leaves the gas mixing chamber. The temperature of the product gas stream is sensed. One or both of the flow valves and/or the operating power of the plasma generator may be used or adjusted to control the temperature of the product gas stream.