A Power Supply Study for the Ramping Dipoles of the Synchrotron Ring of the CNAO Project

A hadrons (Protons and light Carbon ions) synchrotron accelerator is in construction under the responsibility of the CNAO (Centro Nazionale di Adroterapia Oncolociga) and INFN finalized to the therapy of deep tumours. The accelerator complex is composed of two ion sources, a linear accelerator, a low energy and medium energy transfer lines that will transfer the ion beam to the synchrotron ring, where the beams will be accelerated to the prescribed beam energy according to the deep to which the beam energy (Bragg peak) and the dose amount must be released. Only one high energy transfer line is foreseen at this stage of the project. This transfer line will drive the beam to three treatment rooms, corresponding to three horizontal beam lines and one vertical beam line. Additional high energy transfer lines are foreseen in second phase of the project. The synchrotron ring is constituted of 16 H shaped bending dipoles that will accelerated the ion beams till to the requested extraction energy. These bending dipoles must be powered by means of a suitable power supply, 3000 A - 1600 V, that must accomplish the acceleration cycle in less than 1.6 s. The characteristics and performances of such challenging power supply are described in this note. A 24 pulse SCR based topology is proposed, and control circuitry simulations are developed together with a deep analysis of the expected output current shape in terms of current ripple and residual current error.