New compact cyclotron design for SPIRAL

The SPIRAL project whose purpose is the production and the acceleration of radioactive nuclei is under realization at GANIL. The new facility uses a cyclotron as a post accelerator taking place behind the present machine. The energy range is 2 to 25 MeV/u according to the Q/A factor of the ions. The magnet structure (550 t) is made of 4 independent return yokes and a common circular pole piece (3.5 m in diameter) with 4 sectors. The average induction needed is 1.56 Tesla with hill and valley gaps of respectively 0.12 and 0.3 m. The required field patterns are adjusted by means of circular trim coils located between the sectors and the pole piece.