Halo formation of intense beam in periodic transport system

In the intense current proton accelerators for driving the radioactive clean nuclear system, the halo particles are most easily lost on the wall of the accelerator, resulting in radioactivity strong enough to exclude the access of workers to the machine for necessary maintenance and to damage some of the elements of the machine. Therefore it is very essential to understand the mechanism of the halo formation for the correct design of this kind of accelerators. The recent advance in the halo studies is introduced at first. And then the halo formation in periodic transport system is investigated by means of single particle-beam core model. Finally, some other approaches to the issue are discussed