Dr Suzie Sheehy

Abstract:

Superconducting, curved magnets can reduce accelerator footprints by producing strong fields (> 3 T) and reducing the total number of magnets through their capability for combined-function multipolar fields, making them an attractive choice for applications such as heavy ion therapy. There exists the problem that the effect of strongly curved harmonics and fringe fields on compact accelerator beam dynamics is not well represented: existing approaches use integrated cylindrical multipoles to describe and model the fields for beam dynamics studies, which are invalid in curved coordinate systems and assume individual errors cancel out over the full machine. In the modeling of these machines, the effects of strongly curved harmonics and fringe fields on compact accelerator beam dynamics need to be properly included. An alternative approach must be introduced for capturing off-axis fields in a strongly curved magnet, which may affect long-term beam stability in a compact accelerator. In this article, we investigate the impacts of deploying a curved canted-cosine-theta (CCT) superconducting magnet in a synchrotron for the first time. We develop a method to analyze and characterize the 3D curved fields of an electromagnetic model of a CCT developed for the main bending magnets of a compact (27 m circumference) carbon ion therapy synchrotron, designed within the Heavy Ion Therapy Research Integration Plus European project (HITRIPlus), and the CERN Next Ion Medical Machine Study (NIMMS). The fields are modelled in the compact synchrotron in mad-x/ptc to study their effects on beam dynamics and long-term beam stability. Results indicate that the synchrotron is able to operate with the presence of the magnetic field gradients, with considerable improvement to the long-term beam stability in the machine after tuning the higher order field gradients. The insights gained through the methods presented allow the optimisation of both magnet and synchrotron designs, with the potential to impact the operational performance of future ion therapy facilities.

Abstract:

In this paper we present a quantitative measurement of the change in frequency (tune) with intensity of four transverse resonances in a high intensity Gaussian beam. Due to the non-linear space charge forces present in high intensity beams, particle motion cannot be analytically described. Instead we use the Simulator of Particle Orbit Dynamics (S-POD) and the Intense Beam Experiment (IBEX), two linear Paul traps, to experimentally replicate the system. In high intensity beams a coherent resonant response to both space charge and external field driven perturbations is possible, these coherent resonances are excited at a tune that differs by a factor $C_{m}$ from that of the incoherent resonance. By increasing the number of ions stored in the linear Paul trap and studying the location of four different resonances we extract provisional values describing the change in tune of the resonance with intensity. These values are then compared to the $C_{m}$ factors for coherent resonances. We find that the $C_{m}$ factors do not accurately predict the location of resonances in high intensity Gaussian beams. Further insight into the experiment is gained through simulation using Warp, a particle-in-cell code.