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.