PURPOSE: To reduce the ripple rate, by phase-regulating the input voltage of each Cockcroft-Walton (CW) circuit by the use of optical fibre in a device where multistaged multiple CW circuits are concatenatingly connected.

CONSTITUTION: A DC high voltage generator is composed of two Cockcroft- Walton circuits (CW circuits) 1∼2 made up of a capacitor C and a rectifier D. These CW circuits 1∼2 are concatenatingly connected, up and down, with the lowest part of the lower stage of the CW circuit 1 and the highest part of the upper stage as input terminals, where the secondary voltage is supplied from charging transformers 3∼4. The phase of input voltage of a transformer 3 is detected with a phase detector 10 and transmitted to a converter 13 through an optical signal converter 11 and an optical fibre 12. On the other hand, the phase of output voltage of a generator 7 is detected with a phase detector 14 and compared with a phase comparator 15. Based on this comparison result, a phase regulator 16 is activated and the voltage phase from the generator 7 to give the transformer 4 is regulated.