Control strategy for the Acceleration voltage of the ITER Neutral Beam Injector

The Acceleration Grid Power Supply of the ITER Neutral Beam Injector is designed to deliver up to 200 kV to each of the five stages of the electrostatic accelerator, producing a total voltage up to -1 MV with respect to ground. In the present design, the output voltages of the dc generators are independently controlled by five closed control loops. The output voltage measurements are obtained from the difference between the grid potential measurements, referred to local ground. Therefore, the control precision for each stage is affected by the amplification of the measurement errors. Thus, an alternative control scheme, based on a single closed control loop and regulator, has been considered. In this paper, the performance of the two control methods in terms of systematic errors, dynamic performance and sensitivity to load variations are evaluated and compared.