Adiabatic Capture of Charged Particles in Stable Islands: A Novel Approach to Multi-Turn Extraction

Recently a novel approach has been proposed aimed at performing multi-turn extraction from a circular machine. Such an approach consists of splitting the beam by means of stable islands created in transverse phase space by nonlinear magnetic elements such as sextupoles and octupoles. Provided a slow time-variation of the linear tune is applied, adiabatic with respect to the betatron motion, the islands can be moved in phase space and eventually charged particles may be trapped inside the stable structures. This generates a certain number of well-separated beamlets. Originally, this principle was successfully tested using a fourth-order resonance. In this paper the approach is generalised to other type of resonances and some examples of adiabatic capture performed by using various low-order resonances are presented and described in detail.