Simulation and Analysis on Stage Capacitor Bank of Symmetrical Cockroft Walton Multiplier Column for 1 MeV, 100 kW DC Accelerator

Electron Beam Centre (EBC), Beam Technology Development Group (BTDG), BARC is developing 1 MeV, 100 kW DC accelerator for Electron Beam Waste Water Treatment (EBWWT). The accelerating potential of -1000 kV DC is generated by Symmetrical Cockcroft Walton Multiplier (SCWM) circuit pressurized at gas mixture of 95%N2–5%SF6 at 6 kg/cm2 pressure for HV insulation. The accelerated electron beam passes through graded accelerating column with vacuum better than 10–6 mbar. The multiplier column is powered through 45 kVp-0–45 kVp, 10 kHz transformer along with IGBT-based inverter and DC power supply (DCPS). The multiplier has 15 stages with stage capacitance of 20 nF, 120 kVDC. The accelerator has been tested at 1000 kV DC at no load and 950 keV at 50 kW beam power. The accelerator was operated at 25 kW level for 24 h continuously. This paper describes the effect of stage capacitance value in the HV multiplier performance. Simulation has been carried for multiplier voltage buildup with variation in stage capacitance. Simulation results, analysis and experimental values have been discussed in this paper.