Trichel Pulse Mode and the Stage Preceding It during Corona Discharge

Study of negative corona discharge in atmospheric air has been performed. The discharge was initiated between point cathode and plane anode placed at a distance of 10–20 mm, radius of curvature of the cathode needle was about 20 µm. It is shown that at the discharge stage preceding the Trichel pulse mode, the discharge current is not detected within the measurement error of ±0.2 nA. It was shown that when voltage across the gap is close to the threshold of corona discharge ignition, after the current of the first Trichel pulse has dropped to 20–25 nA during ∼250 µs the current continues to decrease to zero within ∼700 µs. It was found for the first time that in a certain range of applied voltage, the Trichel pulse mode after its initiation becomes unstable and periodically changes to a pulseless discharge mode with a current of $$ \lesssim {\kern 1pt} 1$$ µA.