Fast photon counting in negative corona discharges in the Trichel regime

Using a fast pulse counting system with a time resolution of 0.7 ns, the intensity has been measured of the light originating from a negative corona discharge in the Trichel regime in air, resolved in time, in position in the gap and in wavelength. The dominant spectral lines originate from the second positive system of N 2 . Both the current and the emission from the plasma carrying the current show a fast increase on a nanosecond timescale and a successive slower decrease. Repetition frequencies are in the MHz range. The maximum of the light pulse intensity corresponds with the maximum of the Trichel pulse. The continuum emission measured originates from the attachment processes during the maximum in the current pulse. The electron density estimated from the continuum measurements is 10 18 m -3 at maximum for air at a pressure of 100 kPa. From observed Cul line emission the sputter rate for positive ions impinging on the cathode tip has been determined to be 4*10 -5 atoms ion -1 .