Replacement of SF6 with N2/CO2 in design of a parallel-fed voltage multiplier for electrostatic accelerator

Two main insulating gases of SF6 and N2/CO2 mixture are employed to increase voltage capability of electrostatic accelerators. SF6 offers more insulating capability, but environmental and technical disadvantages of SF6 makes usage of N2/CO2 mixture a desirable option. This paper aims to replace SF6 with N2/CO2 in design of a 500 kV/30 mA parallel-fed voltage multiplier. High-voltage section of the accelerator is a capacitive structure which in combination with rectifying elements, generates the accelerating high-voltage. The structure which is called Voltage Multiplier Capacitive Structure (VMCS) is designed and analyzed in this paper. The first structure is designed to employ SF6 as insulating gas (VMCS500). Then, the structure is modified to be capable of using N2/CO2 as insulating gas with lower breakdown voltage (VMCS500-m). The modified structure requires more complex mechanical manufacturing process, but offers the simplicity of using N2/CO2 mixture, the option of using the modified structure with superior SF6 gas, increasing the output voltage and beam energy. CST EM STUDIO was used for capacitance calculation and electric field analysis. LTSPICE was used for equivalent circuit analysis of the high voltage generating section.