A new 3-phase ac plasma reactor has been developed within the framework of research on hydrocarbon cracking for the production of carbon black and hrydrogen.((1,2)) One of the main characteristics of the system is related to the 3-phase 50 Hz ac current plasma generator which induces a very particular are motion affecting the heat and mass transfer inside the reactor. In a first step, the general flow inside the reactor in the absence of hydrocarbon injection has been studied. A simplified approach to characterize the heat and mass transfer inside the reactor is presented in this paper. The are zone analysis is carried out simultaneously by a theoretical analysis of the electromagnetic forces and by an ultrahigh-speed cine-camera analysis. The flow in the reactor. is modeled with a CFD commercial code. Results are compared with experimental temperature measurements.