A novel method for multiturn extraction from a circular particle accelerator is presented, based on trapping particles into islands of phase space generated by nonlinear resonances. By appropriate use of sextupoles and octupoles, stable islands can be created at small amplitude in phase space. By varying the linear tune, particles can be trapped inside these islands and then transported towards higher amplitudes for extraction. Results of numerical simulations are discussed.

Recently a novel approach has been proposed for performing multiturn extraction from a circular machine. Such a technique consists of splitting the beam by means of stable islands created in transverse phase space by magnetic elements creating nonlinear fields, 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 generalized by considering other types of resonances as well as the possibility of performing multiple multiturn extractions. The results of numerical simulations are presented and described in detail. Of course, by time reversal, the proposed approach could be used also for multiturn injection.

This paper is an updated review of the collective effects observed and predicted in The CERN-PS machine for the LHC beam. Workshop on Instabilities of High Intensity Hadron Beams in RingsAt Brookhaven National Laboratory, Upton, N.Y., June 28 to July 1, 1999 Abstract. This paper is an updated review of the collective effects observed and predicted in the CERN-PS machine for the LHC beam.

The beam-induced electron cloud buildup is one of the major concerns for the SPS and the design of the future LHC. During the 2000 run, this effect has also been observed in the PS with the nominal LHC-type beam. The electron cloud induces a baseline distortion in electrostatic pickup signals, both during the last turns in the PS, when the full bunch length is reduced to less than 4 ns, and in the transfer line between the PS and the SPS rings. In the year 2001, modifications in the rf hardware allowed us to study the properties of the beam instability related with the electron cloud phenomenon for a total bunch length of about 10 ns. The complete set of experimental observations carried out in the PS machine is presented and discussed in detail.

The beam-induced electron cloud build-up is one of the major concerns for the SPS and the design of the future LHC. Recently, this effect has been observed also in the PS with the nominal LHC-type beam, consisting of a batch of 72 bunches of 1.110 11 p/b spaced by 25 ns. The electron cloud induces baseline distortion in electrostatic pick-up signals that is observed, both in the last turns of the PS when the full bunch length is reduced to less than 4 ns, and in the transfer line between the PS and the SPS rings. Experimental observations are presented and compared to simulation results and predictions from theory. Furthermore, possible cures, such as variation of the bunch spacing, inserting gaps in the bunch train and applying weak solenoidal fields, are also discussed.