10 kV square wave generator

A 10 kV square wave generator was constructed and tested. The generator consists of a DC high voltage source, a pulse forming line (PFL) made from 50 ohm commercial cable, a spark gap switch filled with pressurized nitrogen and a pulse transmission line (PTL) made from the same cable as PFL. By changing the PFL length the pulse width of the generator could be changed. The amplitude of the output voltage pulse varying from 3 kV to 10 kV could be easily obtained by changing the nitrogen pressure. Experiments show that the rise time t_r of square wave output from the generator is in the range of 14.1 ns to 1.5 ns when the nitrogen pressure filled in the spark gap varies from 0.2 MPa to 0.7 MPa. It was found that t_r is proportional to p^-1.78,which is different from the result of t_r^∝p^-5/6, derived basing on the famous J.C.Martin formula. The 0.4mm gap filled with pressurized nitrogen of 0.7 MPa was broken down at an electric field as high as 500 kV/cm, which made t_r much shorter.