Ionization Cooling using Parametric Resonances

Abstract

(Dr. Yaroslav Derbenev, Subcontract PI). The project was to develop the theory and simulations of Parametric-resonance Ionization Cooling (PIC) so that it could be used to provide the extra transverse cooling needed for muon colliders in order to relax the requirements on the proton driver, reduce the site boundary radiation, and provide a better environment for experiments.During the course of the project, the theoretical understanding of PIC was developed [1,2] and a final exposition is ready for publication [Appendix I]. Workshops were sponsored by Muons, Inc. in May and September of 2007 that were devoted to the PIC technique [3]. One outcome of the workshops was the interesting and somewhat unexpected realization that the beam emittances using the PIC technique can get small enough that space charge forces can be important. A parallel effort to develop our G4beamline simulation program to include space charge effects was initiated to address this problem [4]. A method of compensating for chromatic aberrations by employing synchrotron motion was developed and simulated [5 and Appendix II]. A method of compensating for spherical aberrations using beamline symmetry was also developed and simulated [6 and Appendix III]. Different optics designs have been developed [7] using the OptiM program in preparation for applying our G4beamline simulation program, which contains all the power of the Geant4 toolkit.However, no PIC channel design that has been developed has had the desired cooling performance when subjected to the complete G4beamline simulation program. This is believed to be the consequence of the difficulties of correcting the aberrations associated with the naturally large beam angles and beam sizes of the PIC method that are exacerbated by the fringe fields of the rather complicated channel designs that have been attempted. That is, while the designs developed and tested using the matrix program OptiM can work well, a real simulation with lumped dipoles, quadrupoles, and solenoids and their associated fringe fields has not succeeded. As a consequence of this realization, a new approach is being attempted that is based on the use of a helical solenoid (HS) channel that is made of simple coils that provide a much more homogeneous magnetic field. However, in order to use the HS a new approach was required to generate a variable dispersion that is needed according to the PIC theory described above. This approach and its first implementation will be described at EPAC08 in June, 2008 [8].In the sections of the report that follow, the general theory of muon beam cooling is described starting from the basic ideas of ionization cooling and ending with the PIC ideas that have been developed in this project. The detailed theory of PIC is presented in Appendix I. The most important papers of the project are presented in subsequent appendices. Discussion of Accomplishments:A preprint of the PRSTAB paper covering PIC theory is shown as Appendix I below. The aberration correction discussion is much more complet...