Summary form only given. This contribution deals with the time resolved diagnostics of a non thermal plasma source initially developed at GREMI for biomedical applications. The set up, designed as Plasma Gun1, consists in a cylindrical Dielectric Barrier Discharge reactor flushed with neon or helium at flow rates of a few tens of cm^.min"1, and powered by fast rising voltage pulse of nanosecond duration ranging between few kV and few tens of kV in amplitude. At the DBD reactor output, transient plasma balls are generated which propagate over very long distances in a dielectric guide having very high aspect ratio (e.g.: a few tenths of millimeters in diameter and a few tens of cm in length) with velocities as high as 5 108cms_1. Very fast energy transfer occurs as the balls reach ambient air leading to the production of radicals and of nitrogen and nitric oxide excited molecular states leading to UV radiations.