Pure nitrogen gas was heated with direct current arc, at input powers from several hundred W to over 5 k W, and then injected through a nozzle into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating the gas to very high speed around 7 km/s. Various structures of the arc generator and gas expansion nozzle were examined. Results show that bypass exhausting of the boundary layer before it enters the nozzle divergent section can greatly increase flow speed of the jet, thus it might be possible to use nitrogen as a working gas in high speed gas dynamic test facilities.att Pure nitrogen gas was heated with direct current arc, at input powers from several hundred W to over 5 k W, and then injected into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating the gas to very high speed around 7 km / s. Various structures of the arc generator and gas expansion nozzle were examined. Results show that bypass exhausting of the boundary layer before it enters the nozzle divergent section can greatly increase flow speed of the jet, thus it might be possible to use nitrogen as a working gas in high speed gas dynamic test facilities.att