## 2 Materials and Methods
### The Resonant Capacitor Charger  
The presented power supply should generate high-voltage pulses with adjustable amplitude and repetition ratio. The repetition frequency of the output voltage pulses was set in the range of 250-2000 Hz. The role of the resonant capacitor charger is to accumulate the energy needed to generate a single voltage pulse in the electric field of a capacitor bank. The charging process must have acceptable accuracy and has to be fast enough to finish in the available time (pause) between output pulses. A simple, resonant construction with two power switches was chosen to reduce the switching loss of the used power semiconductors, and to make the charging process as efficient as possible.  
Figure 1: Proposed pulsed power supply for non-thermal plasma reactors. Three main stages are marked: DC voltage source (**blue**); resonant capacitor charger (**red**); and output pulse shaping unit (**green**).  
The proposed topology acts in three repetitive intervals, as shown in Figure 2. The analytical description of this part of the topology and each separate interval were presented in [11].  
The proposed resonant charger consists of two series of monoresonant RLC (resistive - inductive - capacitive) circuits connected in a cascade. In the real power supply construction, inductors L1 and L2 were made of single MS-250026-2 micrometals cores with 15 turns each using litz wire windings of \(\sim\)5.8 mm\({}^{2}\) of copper wire to obtain an inductance of 22 uH. R1 and R2 are the parasitic resistances of inductors, wires, and printed circuit board tracks, in the real construction, the measured value was 17 m\(\Omega\). The core material used is called SENDUST, and it is designed for high-frequency power application inductors. The C1 capacitance has a measured value of 12 nF in the prototype and is made of WIMA FKP capacitors connected in series, due to the high dV/dt operation of that power supply stage. The C2 capacitance is a 1 uF capacitor bank made of nine 1 uF WIMA FKP capacitors connected in a mixed (parallel series) way, due to the high value of the capacitor current. Figure 3 shows the constructed resonant capacitor charger module and the C2 capacitor bank.  
Figure 3: **(a)** The resonant capacitor charger and **(b)** the C2 capacitor bank.  
Figure 2: **(a)** The three intervals of capacitor charger operation and **(b)** simulated waveforms. PLECS® simulation platform was used for calculations. Interval 1 (top)—the energy of the input source is resonantly transferred to capacitor (with voltage boost effect) C1. Interval 2 (middle)—the energy of capacitor C1 is resonantly transferred to C2 and increases the voltage across C2. Interval 3 (bottom)—the resonant energy stored in the magnetic field of L2 is used to charge C2 using the freewheeling diode D3.  
For those values of the real L and C components, the charging of C\({}_{1}\) capacitance takes 1.5 \(\upmu\)s and the energy transfer between C\({}_{1}\) and C\({}_{2}\) takes 1.5 \(\upmu\)s. To fully charge the C\({}_{2}\) capacitor, 30 repetitions of three charging intervals are needed. The power switches S\({}_{1}\) and S\({}_{2}\) were 1700 V, 72 A, 45 m\(\Omega\) SiC power MOSFETs C2M0045170D from Cree. The diodes D\({}_{1}\)-D\({}_{3}\) were 1700 V, 10 A SiC power Schottky diodes GB10 MPS17 from GeneSiC Semiconductor Inc. The diodes D\({}_{1}\) and D\({}_{2}\) prevent the reverse flow of energy and, therefore, a low reverse recovery current feature of SiC diodes could be used. The role of the diode D\({}_{3}\) is to block the negative current flow of the resonating tank to exclude negative voltages on the capacitor C\({}_{1}\).