Category: Beam Dynamics

Speaker: Lucy Martin

Speaker: Francois Meot

Abstract: Litvinenko-Roser’s alternative approach for Future Circular electron-positron Collider uses energy recovery linac recirculators to mitigate the otherwise enormous power consumption needed to compensate for 100 MW of beam energy loss by synchrotron radiation in a ring-ring design. This approach would also allow to extend CM energy to 500 GeV (or above) for double Higgs production. An advantage of the linac-linac scheme is its allowing polarized beams. A 100 km, 220 GeV linear FFAG loop is subjected to bunch transport simulations, including SR and polarization survival.

Speaker: Stephen Brooks

Abstract: The CBETA ERL has a fixed-field (non-scaling FFA) return loop, which recirculates up to four different energies: 42, 78, 114, 150MeV.  Although most of the field is provided by permanent magnets, there are electromagnetic correctors that can superimpose a dipole field that can be changed during operation.  These dipole kicks affect the energies in different ways, since they have different cell tunes.  This allows independent control of the beams over a long distance by using combinations of correctors determined by Singular Value Decomposition (SVD).  To operate correctly in reality, at CBETA a “semi-empirical” response matrix was used in the SVD, which was adjusted to more exactly match the observed phase advances of the machine.  With this approach, all four beam orbits could be corrected. First observations of beam halo, operational tooling, beam steering procedures and path length adjustment techniques developed for CBETA are also reported.

Speaker: David Kelliher

Abstract: A key requirement of future neutron spallation and muon sources is flexibility of operation to best serve multiple target stations. Beam stacking allows a rapid cycling, high intensity machine to operate at lower repetition rates but with higher peak output. The effect of phase displacement and scattering on the stacked beam is described, revisiting theory first developed during the MURA years. We go on to show how beam stacking can be achieved both in the ISIS2 vFFA and its prototype ring. We also consider the choice of RF cavity technology.

Speaker: Max Topp-Mugglestone

Abstract: The form of magnetic fields required to realise the scaling Vertical excursion Fixed Field Alternating gradient accelerator (VFFA) can imply strong solenoid fringe field components for certain lattice configurations in addition to the skew quadrupole components in the magnet body – both of which in turn imply coupled dynamics that will need special treatment. Currently, all modelling procedures for these machines rely on computationally intensive simulations, and optimisation and lattice design processes require time-consuming parameter scans. Using a method based on the standard Hamiltonian formalism as seen elsewhere in accelerator physics, first steps towards realising and testing a fully analytic model of the VFFA that accounts for the uniquely coupled dynamics of the system are presented. This analytic model would provide a means for rapid lattice design, optimisation, and benchmarking, as well as enabling us to develop an understanding of the effects of various key lattice parameters, such as the VFFA field index m. A rudimentary transfer-matrix based optics code using this model is demonstrated in the context of a muon collider lattice, as well as a number of other sample lattices.

Speaker: J. Scott Berg

Abstract: CBETA is an energy recovery linac with four accelerating and four decelerating passes, where all of the beams return to the linac through a single linear fixed field alternating gradient arc. I will describe the methods we used to correct the orbits for the 7 beams with four distinct energies in this return arc. Each of the 107 FFA doublet cells had a horizontal and a vertical corrector as well as a beam position monitor. Two techniques were used. The first applied a singular value decomposition to find changes in corrector settings that would minimize the orbit error in some region of the machine. The second would find combinations of correctors in one region that would correct the orbit and/or dispersion in a downstream region for a single pass while leaving the orbit and/or dispersion unchanged in previous passes. I present details of these methods, describe how we applied them, and indicate practical and theoretical difficulties we encountered.

Speaker: David Kelliher

Abstract: The RF program in FFAs, freed of the requirement to follow a ramping bending field, can be chosen with great flexibility. It is of interest to determine how rapidly the RF parameters can be varied without leading to an increase in longitudinal emittance. Here, making use of the KURNS 150 MeV FFA, we experimentally investigate adiabaticity by ramping the synchronous phase to zero at varying rates. From the resulting bunch monitor data, longitudinal tomography is used to calculate the emittance before and after the ramp and the results are compared with simulation.

Speaker: Bruno Muratori

Abstract: Laser wakefield acceleration, together with other types of novel acceleration techniques, has seen considerable progress of late. Together with this progress comes a question, which has only recently started to be addressed, of how to transport and utilise such beams. This is a challenge because of the high initial divergence of these beams. There are several approaches to this problem and we concentrate on one in this paper and look at the implications of it in some detail. The approach we take is to have an FFAG channel made of permanent possibly Halbach magnets. In particular, we look at the implications of quadrupole fringe fields on the aperture of these permanent magnets. It has recently been shown that the pole shape of the quadrupoles influences the fringe field and, further, can have a particularly large effect the more the beam goes off the transverse axis. This could lead to a further restriction in aperture, above the one due to the divergence of the beam exiting the plasma. Several properties of this channel as well as possible geometric rearrangements of it are also discussed.

Speaker: Lucy Martin

Abstract: In Nonlinear Integrable optics (NIO), a highly nonlinear magnet is inserted into a lattice with linear focusing (known as a T-insert), resulting in regular and bounded particle motion, where particles do not experience resonant excitation. NIO is a new and complex concept with clear advantages for intense beams in circular machines. The concept of NIO is being tested at Fermilab (IOTA) and the University of Maryland (UMER), but the natural chromaticity and dispersion of small circular accelerators make this process challenging. We performed detailed simulations to ascertain whether a simpler version of this theory, Quasi-Integrable nonlinear Optics (QIO), can be tested in a Paul trap. A Paul trap confines ions transversely with alternating gradient focusing, and so the transverse motion of particles in a Paul trap mimics the transverse motion of particles in an accelerator. In the Paul trap particles are extremely low energy and so can be lost without damaging the trap or irradiating and activating components and the number of ions stored in the trap can be varied so that space charge effects are included. The IBEX Paul trap, located at the Rutherford Appleton Laboratory, Oxfordshire (UK), has previously been used to experimentally explore the dynamics of intense beams. This talk describes the design process for a T-insert which meets the constraints of QIO, as well as the constraints imposed by the IBEX hardware. A number of T-insert lattices were tested on the IBEX trap, confirming that enough ions were confined to study QIO in the presence of space-charge forces and that it is possible to create a T-insert with sufficient precision. To verify that the T-insert lattice created within the Paul trap met the conditions for QIO, a method to measure the beta function in a Paul trap was designed and tested. These studies represent the first steps towards testing QIO and NIO in the simplified system of the Paul trap.