The CNAO (National Center for Oncological Hadrontherapy), located in Pavia, is the first Italian center for deep hadrontherapy with proton and carbon ion beams [1]. The CNAO synchrotron initial commissioning has been carried out using proton beams in the full range of energies: 60 to 250 MeV/u. The first foreseen treatments will need energies between 120 and 170 MeV/u. The nominal proton currents have been reached. The energy scaling of the synchrotron systems and parameters leads to an extracted energy that matches the measured particle range better than 0.1 mm, fitting the treatment requirements, with repeatable beam size and beam current in the treatment room at all investigated energies. A summary of the main results of the synchrotron commissioning is presented. MULTI-TURN INJECTION The CNAO [1] synchrotron is a 78 m long ring, in which the beam is injected at 7 MeV/u and accelerated to energies between 60 MeV, minimum energy for protons, and 400 MeV/u, maximum energy for carbon ions. The lattice is based on two symmetric and achromatic arcs joined by two non-dispersive straight sections. MultiTurn injection (MTI) results in an injected beam which occupies all the synchrotron length (Trev ~ 2μs). Pick-ups provide useful signals only after RF capture, but using a 1 μs chopped beam it has been possible to measure the beam position during the first turns, useful tool for the first commissioning period. Figure 1 Multiturn injection measured on three pick-ups without adiabatic trapping with 1μs beam and 30μs beam. The design efficiency of MTI is 1.9 equivalent turns, that is the injected charge should be the one contained in 1.9 Trev IMEBT, (1.4 10 10 injected protons for IMEBT = 600μA). The measured number of injected particles is much larger than the design one but there is a loss in the initial phase and during acceleration, which results in a number of accelerated particles equal to the specified one, with margin for improvement. MACHINE CYCLE AND RF CAVITY The machine cycle is designed to assure repeatability: the synchrotron magnets are ramped to their maximum field after every extraction, so that the same hysteresis loop is followed, independently of the beam extraction energy. Figure 2 illustrates the magnet cycle and the acceleration. The blue line represents the synchrotron dipoles field, the yellow one is the DCCT, the green one is the signal on a pick-up and the pink one is the voltage of the betatron core used for extraction. The DCCT rises quickly at injection, shows some losses during capture and acceleration and decreases linearly during extraction. The Pick-up signal disappears when the beam debunches as RF is switched off in preparation of extraction. Figure 2: Signals shown on the control room scope: DCCT, B field, Pickup, Betatron core voltage. The main machine cycle phases are identified: a) injection, b) acceleration ramp, c) start extraction. The RF cavity [2] has played a fundamental role in the synchrotron and extraction lines commissioning. It controls the beams during the critical moments of the whole cycle. After the multiturn injection the beam is unbunched: an adiabatic capture is performed controlling with precision the cavity voltage at low values (20-150 V), to avoid increasing longitudinal emittance. During the acceleration beam loops implemented in the low level RF damp the synchrotron oscillations fixing the beam energy despite possible irregularities in the dipole ramps[3] by controlling the beam phase and position in a high dispersion pick up. When acceleration is completed, the RF cavity finely adjusts the beam energy (in the range of Δp/p ~ 10). Before RF switching off to debunch the beam, the RF phase jump is used to increase the beam energy spread up to the extraction value with a uniform distribution. During extraction, the technique of empty bucket channelling reduces the ripple spill [4]. WEPS007 Proceedings of IPAC2011, San Sebastian, Spain 2496 C op yr ig ht c ○ 20 11 by IP A C ’1 1/ E PS -A G — cc C re at iv e C om m on sA tt ri bu tio n 3. 0 (C C B Y 3. 0) 04 Hadron Accelerators A04 Circular Accelerators