## 1 Introduction  
Electroporation is a transient or permanent increase in biological cell membrane permeability when subjected to high intensity electric field pulses [1]. The treatment outcome depends on the pulse parameters, including waveform, duration, amplitude, frequency, etc. [2; 3]. As a result, pulsed power electronics became an inseparable part of electroporation or techniques associated with this method. Therefore, the development of pulsed power systems for electroporation, known as electroporators, is constant [4; 5; 6; 7; 8; 9; 10]. With the development of semiconductor technology, the area of electroporation applications is also transitioning towards a shorter pulse range (i.e., use of nanosecond pulses) [11; 12; 13; 14]. The short but high intensity pulses can target intracellular structures without porating the cell itself [15; 16]. Additionally, with the use of nanosecond protocols, modulation of cell death is possible, which is useful to minimize inflammation of the tissue [17]. Recent developments show the high potential of the high frequency irreversible electroporation (H-FIRE) methodology when sequences of high frequency pulses are used to permeabilize the cells [18; 19; 20]. At the same time, the 100 kHz-10 MHz pulse repetition range is poorly covered due to a lack of technological infrastructure. To address the problem, in the past 2-3 years, a variety of novel high frequency electroporation systems were proposed. In 2019, [PERSON] et al. presented solid-state unipolar positive Marx generators positioned back to back to generate high frequency bipolar pulses [21]. The system is capable of forming up to 5 kV bipolar pulses, with 500 ns-10 \(\upmu\)s pulse widths and 200 ns-10 \(\upmu\)s relaxation times between positive and negative pulses. In 2021, [PERSON] et al. showed a prototype of an asymmetric bipolar pulse generator [22]. The developed device is able to generate up to 4 kV pulses with a minimal 200 ns duration and 2 MHz pulse repetition frequency. In 2018, [PERSON] et al. presented a prototype with multiple stacks of MOSFETs in parallel to create multiphase outputs with pulses as short as 80 ns [23]. Recently, [PERSON] et al. published a 6.5 kV four-channel generator for 100 ns-100 \(\upmu\)s pulses for use in biomedical applications [24]. In all cases, silicon-carbide (SiC) MOSFETs were used, which became a popular technology for the generation of high frequency high power bursts [25]. One of the problems, which is common for sub-microsecond pulse forming systems, is the impedance matching to prevent any reflections [26]. In the electroporation context, depending on the cell buffer, tissue heterogeneity, type, and structure of electrodes, the impedance of the load may vary from tens of \(\Omega\)[27] to several k\(\Omega\)[28]. Therefore, quite frequently, the electroporator is shunted with sub-100 \(\Omega\) resistance. This is a sub-optimal solution since it draws almost double the power from the generator and also does not solve the impedance matching problem completely. The impedance will still vary since the load is connected in parallel with the shunting resistance. To solve the problem, we have previously proposed a unipolar electroporation system featuring a controlled crowbar circuit [4], which cuts the pulse fall-time and, thus, ensures constant rise and fall times independently from the load. A similar concept was recently used by [PERSON] et al. [5]. In the context of electroporation, ensuring constant rise and fall times is crucial due to the dependence of the biological effects on the polarization of the cellular membrane [29]. In this work, we wanted to combine the various recent electroporator concepts into one machine and produce a novel multiphasic electroporation system. The new system must support pulse repetition frequencies higher 1 MHz, feature a double-crowbar circuit to diminish the impedance matching problem, and be capable of generating pulses shorter than 200 ns.