一、引言我所1.2m迴旋加速器原为固定能量加速器,1969年底,曾初步改为可变能量加速器,但磁场分布偏离等时性要求较高,因而束流性能差。1975年初,我们着手对器的性能作进一步改进,于1980年底,改为扇形等时性可变能量加速器。设计能量W_D=3～14MeV; I. INTRODUCTION My 1.2m cyclotron was originally a fixed energy accelerator. At the end of 1969, it was initially changed to a variable energy accelerator. However, the magnetic field deviates from the isochronous requirements and thus has poor beam performance. In early 1975, we set out to make further improvements to the performance of the device, by the end of 1980, to a fan-shaped isochronic variable energy accelerator. Design energy W_D = 3 ~ 14MeV;