Abstract: The Townsend to glow discharge mode transition was investigated in the dielectric barrier discharge (DBD) helium
plasma source which was powered by 20 kHz / 4.5 kVrms high voltage at atmospheric pressure. The spatial profile of
the electric field strength at each modes was measured by using the intensity ratio method of two helium emission lines
(667.8 nm (31D → 21P) and 728.1 nm (31S → 21P)) and the Stark effect. ICCD images were analyzed with consideration
for the electric field property. The Townsend discharge (TD) mode at the initial stage of breakdown has the light emission
region located in the vicinity of the anode. The electric field of the light emitting region is close to the applied field in
the system. Immediately, the light emitting region moves to the cathode and the discharge transits to the glow discharge
(GD) mode. This mode transition can be understood with the ionization wave propagation. The electric field of the emitting
region of GD near cathode is higher than that of TD near anode because of the cathode fall formation. This observation
may apply to designing a DBD process system and to analysis of the process treatment results.