Compact high-voltage, low-impedance nanosecond pulse generators for biomedical applications

The application of pulsed electric fields with durations in the range of nanoseconds and field strengths on the order of hundred kilovolt per centimeter has demonstrated great potential for the treatment of cancer cells. However, successful exposures require the generation of high voltage pulses that can be sustained across a load with an impedance that is often much lower than 100 ohm. A second challenge is the wish to expose cell suspensions in large volumes and eventually also extended tumors. These requirements are driving the development of pulse generators that can provide pulses with amplitudes of several tens of kilovolts across loads of only a few tens of ohms. In addition pulse generators should be small and portable to bring them to different treatment sites and patients, respectively. Many nanosecond pulse generators that are currently used for biomedical studies rely on transmission line configurations. With this straight forward approach it was possible to develop pulse generators which allow the exposure of samples with an impedance as low as 10 ohm. However, the pulse amplitude across a matched load is generally limited to values of 30-35 kV. An increase of the pulse voltage is possible with Marx-bank topologies and we have constructed a system providing a peak voltage of 90 kV in a pulse with a duration of about 250 ns across a load with an impedance of 300 Ω. However, this pulse is not rectangular. To provideamplitudes. Pulse forming networks and Blumlein line pulse generators were investigated. In particular we studied systems that are based on the concept of stacked Blumlein lines.lines. Several systems for the generation of 100-ns pulses were built and used in experiments with different biological loads.