Performance of a low impedance nanosecond pulse generator

Nanosecond pulse generators (NS-PG), able to generate high voltage pulses with duration of 5 ns and fast rise and fall times of 2 ns, enable higher energy efficiencies of plasma processing. Here, we discuss development of a high-current output, low impedance NS-PG with high processing capacity for applications such as ozone generation and exhaust gas treatment. Our NS-PG consists of a microsecond pulse generation circuit as a charging unit and a nanosecond pulse forming line based on a Blumlein line configuration. This study focuses on the nanosecond pulse forming line, consisting of a spark gap switch (SGS) as a self-closing switch, a triaxial Blumlein line as a pulse forming line, and a transmission line from the Blumlein line to load. SF6 gas filled the SGS, and the output voltage of the generator was regulated by varying the pressure of the gas. Blumlein and transmission lines, previously filled with silicone oil, here used ethylene glycol to reduce characteristic impedance of the NS-PG. In addition, the length of the Blumlein line and the structure of the SGS were also changed to improve the performance of the low impedance NS-PG. This paper presents both the performance of several NS-PG configurations made in the development process of the low impedance NS-PG and switching performance of the new low inductance SGS. All experiments were conducted using a matched register as load for each generator. Results show that peak current of the low impedance NS-PG with the new SGS was 3 times higher than that of the previous NS-PG; also, the new SGS demonstrated different switching characteristics from that of the conventional one in both pressure and frequency characteristics.