Implementation of a coupled treatment of the one-turn mapping in the ray-tracing code Zgoubi
The spin is an intrinsic property of elementary particles and is considered as a quantum angular momentum. It is defined by a direction which is either up or down and an absolute value which is proportional to the elementary quantum of action. It has no analogue in classical mechanics but, as the angular momentum in classic mechanics, the spin of composite systems such as the proton is a combination of its spin components. Although knowing the proton components and their spin, their contribution to the proton spin is unknown and the physicists are still trying to unravel the mystery. A recent theoretical work suggests that the contribution carried by the gluons may be large but it has to be confirmed experimentally. The main accelerator facility which is looking for answers about the origin of the proton spin is located at the Brookhaven National Laboratory (Upton, New York, United States of America). This laboratory has the biggest accelerator complex dedicated to the colliding of polarized proton beam. The protons are first supplied by the Optically Pumped Polarized Ion Source (OPPIS), followed by a 200-MeV Linac and are then transferred to the Booster synchrotron. The protons go into the Alternating Gradient Synchrotron (AGS) which accelerate and prepair them to be injected into the Relativistic Heavy Ion Collider (RHIC). Finally the proton beam is stored into the RHIC ring for several hours and supplies collisions in two detectors of particle experiments placed. The data collected are used for studying the decay products of polarized proton collisions. Although the current RHIC spin experiments are already providing the first information about the proton's spin origin, the complex RHIC is still under improvement. Indeed it is working at minimizing undesirable effects which damage the beam polarization along the acceleration. The polarized proton beam is prone to depolarization due to spin resonances. They could be partially avoided by improving the control of some beam parameters. For instance coupling between the two transverse motions occurs in AGS and modifies the beam parameters predicted by the simulations. The locations of all the coupling sources in the AGS are not really known which makes their removal or compensation difficult to elaborate. This requires improving the simulations of beam dynamics made in the AGS. They need to be performed with, on one hand, a very accurate model and, on the other hand, a code capable of analyzing a coupled motion. Two codes are mainly used: MADX and a ray-tracing code called ZGOUBI 4 which is developing by Dr. François MÉOT. It is scheduled to install ZGOUBI onto the computers of the RHIC complex main control room in order to facilitate and extend its use. Nevertheless ZGOUBI is not completely able to deal with coupled one-turn mapping produced by the ray-tracing so it is necessary to find a way of treating the coupled systems and to implement it within the existing code, that will allow producing coupled optical functions and transporting them using the ray-tracing method. The purpose of this report is to present the results of my research work performed during this 5-month internship. It mainly consisted in searching and synthesizing the appropriate formalism in order to fully treat the coupled which outcomes from ZGOUBI. It required to nd a way of implementing it into the existing ZGOUBI code then to test it. Finally after validation of these add-ons some simulations have been handled by ZGOUBI for the AGS.