Multi-beam acceleration in FFAG synchrotron

The first acceleration of protons in a FFAG (Fixed Field Alternating Gradient) synchrotron was demonstrated at KEK in June 2000. Since the magnetic field in the FFAG is static, therefore the repetition rate depends only on the acceleration frequency. We have developed a high gradient rf cavity using the 'FINEMET' magnetic alloy cores. With this new type of rf cavity, the, cycle time of the synchrotron can become very high, 1 kHz or more, which is more than 100 times of the ordinary synchrotron. Thus, the FFAG is an attractive machine for accelerating intense beams. Moreover, the FFAG can accelerate not only single bunch, but also several bunches each having a different energy, by changing the rf frequency for each bunch. The new type rf cavity using the FINEMET cores has a low Q-value which easily enables the coexistence of different frequencies. We have demonstrated this multi-energy, multi-bunch acceleration at the KEK POP FFAG machine.