A gas injector including in which a gas is passed through high-voltage/low-current electrical discharges before being discharged into the chamber of a thermal treatment furnace. The electrical activation of the gas accelerates desirable reactions between the gas, gases in the furnace chamber, and the chamber workload. Preferably, a hot electrode is electrically charged and the other parts of the gas injector and the furnace are grounded. Also provided is a method for activating an atmosphere within the reaction chamber of a controlled-atmosphere reactor.