Status of a 220KV–60NS flat top double pulse genera

The design of multi-pulses multi giga-watt high voltage generators has been of particular interest for electron beam accelerator applications. The major requirements for this type of pulsed power generators are a 1% flat top, a jitter of few nanoseconds, an high reproducibility and a drastic reliability. As an opportunity for future radiographic applications, CEA is working on such double pulse generator as an opportunity to improve its radiographic facilities. This paper proposes a status of the works performed on this generator. The discharge of two 500kV, 12.5Ω pulse forming lines connected in series initiates the two HV pulses. As the generator is composed of two sets of lines in parallel, its impedance is 6.25Ω. Main pressurized air spark-gap switches are triggered by a 55mJ 266nm Nd:YAG laser. We studied the jitter and the delay variation of this spark gap switch as a function of laser pulse energy, gas pressure and position of the laser focal spot into the gap. We report a 3σ 550ps jitter operation with pulse rise time inferior to 7ns. Fifty shots series have been done for the first pulse to know the whole reproducibility of the generator. On a 6.25Ω resistive load, 220kV, 60ns, 2% flat top pulses have been achieved. Jitter observed on a 50 pulses series is less than 3ns. Double pulse experiments were done recently, only preliminary results are presented here. Further works have to be done to improve the flat top of the second pulse.