NANOSECOND PULSE GENERATOR USING DIODE OPENING SWITCH FOR CELL ELECTROPERTURBATION STUDIES ∗ Tao Tang, Fei Wang, Andras Kuthi, and Martin Gundersen ξ Department of Electrical Engineering-Electrophysics, University of Southern California Los Angeles, CA 90089, USA ∗ This work was primarily funded by the Compact-Pulsed Power MURI program funded by the Director of Defense Research and Engineering (DDR&E) and managed by the Air Force Office of Scientific Research (AFOSR) and was also funded by the Army Research Office (ARO) ξ email: mag@usc.edu Abstract Studies of short pulse cell electroperturbation require high-voltage nanosecond pulses delivered to low- impedance electroporation cuvette loads. We present the design and operation of such a pulse generator based on series and parallel connected ordinary rectifying diodes as an opening switch. The generator is designed to produces 5 ns wide, 10 kV amplitude pulses into a 10 Ω cuvette load. The design incorporates a primary IGBT switch. Pulses produced by the IGBT are compressed by one low- loss, nanocrystalline, saturable core compression stages. The compressed pulses are fed to the diode opening switch through a fast, ferrite saturable core transformer. The all-solid-state design results in reproducible pulses and reliable, long-life operation. The prototype system currently generates pulses of 18.4 ns wide and 4.56 kV amplitude under repetition rate of 20 Hz. I. INTRODUCTION High voltage nanosecond electric pulse is essential to the electroperturbation study of biological cells. The response of the cells upon electric pulse exposure depends on the pulse width and amplitude. Pulse longer than 1μs normally results in electroporation, which stands for opening of pores on outer cell membrane temporarily or permanently [1]. When the duration of the pulse reduced to nanosecond range, the cell nuclei can be affected without adversely affecting the outer cell membrane. Further experimental investigations of electroperturbation require compact pulse generators with readily variable output parameters [2]. The desired pulse amplitude and duration is determined by the required electric field and electrode geometry. In order to generate 5-10 MV/m electric field in a standard cuvette load with 1mm electrode gap, pulses with 5-10 kV in amplitude are required. A repetition rate of around 10 Hz is also preferred for the observation of the effects with good statistics. Previous diode pulse generator designed for electroperturbation research can only generated pulses with 600 V in amplitude into 50 Ω load [3], which is good for microscopic study of the cells suspended in micro- chamber. In order to expose massive cells to electric pulses for further experiment, a larger chamber like the standard cuvette is necessary. Shifting to cuvette camber results in reduction of load impedance from 50 Ω to 10 Ω. As a consequence of adopting standard cuvette in experiment, the peak current for the diode to interrupt increases dramatically from 30 A to 1000A. Switching such a large current to the load in only a few nanoseconds raises great challenge. In this situation, the parasitic inductance significantly worsens the performance of the pulse generator. In current version of pulser, the output pulse is only 4.56 kV in amplitude and 18.4 ns in width. Further improvement is in progress to tackle this problem. II. DESIGN As an improved version to its predecessor, the system can be seen as a magnetic compression stage cascading into a diode pulse generator similar to previous design. The circuit diagram is shown in Fig. 1 (a). In the magnetic compression stage, the initial pulses (3 kV, 1μs) are generated by switching the IGBT. Then these pulses are compressed from 1us to 100ns by saturable inductor L 1 . The recovery diode switch stage takes these pulses as its input. The working principle of this stage is very similar to previous diode pulser [3]. Briefly speaking, in this stage, the pulse will first be compressed by a factor of 2 through the saturable transformer T 2 . This way, 1 kA peak current is generated in the energy storage inductor, which is the leakage inductor of transformer T 2 . Once reaching 1 kA, the reversed current through this inductor will be commuted into the cuvette load by the diode opening switch and a 10 kV pulse will be generated. The stage-by-stage design starts from calculating required pulse parameters at the load and works backwards to IGBT switch. The picture of constructed pulse generator is shown in Fig. 1 (b). 0-7803-9189-6/05/$20.00 ©2005 IEEE. 1258