Kurashima, S. Fukuda, M. Kashiwagi, H. Miyawaki, N. Okumura, S. Satoh, T. Yoshida, K. Yuyama, T. JACoW Geneva, Switzerland 978-3-95450-167-0 10.18429/JACoW-Cyclotrons2016-MOB01 English 16-20 MOB01 ion cyclotron acceleration controls vacuum Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-Cyclotrons2016-MOB01 http://jacow.org/cyclotrons2016/papers/mob01.pdf We have been improving a beam quality of the TIARA (Takasaki Ion accelerators for Advanced Radiation Application) cyclotron to form a heavy-ion microbeam with a spot size about 1 μm. The microbeam is used to irradiate such as living cells and semiconductor devices. In order to form the microbeam using focusing lenses, an energy spread on the order of 10⁻⁴ is required to eliminate chromatic aberration in the focusing lenses. A flat-top acceleration system using the fifth-harmonic frequency of the acceleration frequency was installed in the cyclotron to reduce the energy spread. In addition, a new center region, a magnetic field stabilization system and an acceleration phase control technique were developed to provide the microbeam stably for beam users. The energy spread of a 260 MeV Ne beam was reduced to 0.05% by the flat-top acceleration, and the microbeam with a spot size of approximately 1 um was successfully formed. However it takes about 8 h to tune the cyclotron and the focusing lenses. A cocktail beam acceleration technique was introduced to quickly change the microbeam to the other one within 0.5 h, and several microbeams can be used in a beam time as a result.