J. Scott Berg

FFAGS for muon acceleration

Due to their finite lifetime, muons must be accelerated very rapidly. It is challenging to make the magnets ramp fast enough to accelerate in a synchrotron, and accelerating in a linac is very expensive. One can use a recirculating accelerator (like CEBAF), but one needs a different arc for each turn, and this limits the number of turns one can use to accelerate, and therefore requires significant amounts of RF to achieve the desired energy gain. An alternative method for muon acceleration is using a fixed field alternating gradient (FFAG) accelerator. Such an accelerator has a very large energy acceptance (a factor of two or three), allowing one to use the same arc with a magnetic field that is constant over time. Thus, one can in principle make as many turns as one can tolerate due to muon decay, therefore reducing the RF cost without increasing the arc cost. This paper reviews the current status of research into the design of FFAGs for muon acceleration. Several current designs are described and compared. General design considerations are also discussed

Amplitude dependence of time of flight and its connection to chromaticity

In general, the time of flight of a charged particle in an accelerator will depend on the particles transverse amplitude. This effect can become important in machines with large transverse emittances, such as muon accelerators. We will describe the effect, its physical origin, and the circumstances where it becomes important. We will then demonstrate that the effect is directly related to chromaticity. We will describe the effect on the longitudinal dynamics in various circumstances, including linacs and fixed field alternating gradient accelerators (FFAGs). We will describe methods for correcting the effect, particularly in FFAGs.

Pulsed synchrotrons for very rapid acceleration

When rapid acceleration is important, synchrotrons with very short pulse times can be used to accelerate particle beams. We will describe rapidly pulsed synchrotrons and their distinction from ordinary synchrotrons. We will introduce a hybrid synchrotron which interleaves pulsed magnets with superconducting dipoles to allow rapid acceleration while still maintaining a high average bending field. We will describe particular characteristics of the lattice design for these machines. We will describe how to design magnets to limit power consumption while still maintaining high fields. We will discuss the impact of the choice and properties of magnetic materials on the magnet performance. We show a magnet design that limits losses in the core while giving a high field by using multiple materials: 6.5% silicon steel for the back yoke due to its low losses at high frequencies, and 3% silicon steel in the pole for its high saturation field. The magnet has a unique coil configuration that minimizes eddy current lo...

Scheme for Ionization Cooling for a Muon Collider

We discuss a complete scheme for production and cooling a muo n beam for three specified Muon Colliders. We outline the parameters for these Muon Collide rs. The scheme starts with the front end of a proposed Neutrino Factory that yields bunch tr ains of both muon signs. Emittance exchange cooling in upward or downward broad helical lattic es reduces the longitudinal emittance until it becomes possible to merge the trains into single bun ches: one of each sign. Further cooling in all dimensions is applied to the single bunches in further upward climbing helical lattices. Final transverse cooling to the required parameters is achi eved in 50 T solenoids that use high temperature superconductor. Preliminary simulations of e ach element are presented. We discuss known challenges.

Injection/Extraction Studies for the Muon FFAG

The non‐scaling fixed field alternating gradient (NS‐FFAG) ring is a candidate muon accelerator in the Neutrino Factory complex according to the present baseline, which is currently being addressed by the International Design Study (IDS‐NF). In order to achieve small orbit excursion, motivated by magnet cost reduction, and small time of flight variation, dictated by the need to use high RF frequency, lattices with a very compact cell structure and short straight sections are required. The resulting geometry dictates very difficult constraints on the injection/extraction systems. Beam dynamics in the non‐scaling FFAG is studied using codes capable of correctly tracking with large transverse amplitude and momentum spread. The feasibility of injection/extraction is studied and various implementations focusing on minimization of kicker/septum strength are presented. Finally the parameters of the resulting kicker magnets are estimated.

The EMMA Lattice

EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non‐scaling fixed field alternating gradient accelerator (FFAG). I will give a basic review of the EMMA lattice parameters. Then I will review the different lattice configurations that we would like to have for EMMA. Finally, I will briefly discuss the process of commissioning each lattice configuration.

Ionization cooling in all phase space planes with various absorber shapes, including parallel-faced absorbers

Abstract Ionization cooling in a straight beamline reduces the transverse emittance of a beam, and has little effect on the longitudinal emittance (generally, in fact, it increases the longitudinal emittance). Once the beamline bends, the introduction of dispersion creates a coupling between the transverse and longitudinal planes. If this coupling is handled properly, one can achieve cooling in all three phase space planes. This is usually done by placing a wedge-shaped absorber in a region where there is dispersion. I will demonstrate using an eigenvalue analysis that there are other configurations of dispersion and absorber shape that will achieve ionization cooling in all phase space planes. In particular, I will show that one can even achieve cooling in all phase planes with a parallel-faced absorber in a dispersion-free region. I will use perturbation theory to approximate the change in the cooling rates due to longitudinal–transverse coupling. I will then describe how the cooling of longitudinal oscillations can be understood via the projection of the “longitudinal” eigenmodes into the transverse plane.

Acceleration for a high energy muon collider

We describe a method for designing the acceleration systems for a muon collider, with particular application and examples for a high energy muon collider. This paper will primarily concentrate on design considerations coming from longitudinal motion, but some transverse issues will be briefly discussed.

Higher Luminosity eRHIC Ring-Ring Options and Upgrade

Lower risk ring-ring alternatives to the BNL linac-ling [1] eRHIC electron ion collider (EIC) are discussed. The baseline from the Ring-Ring Working Group [2] has a peak proton-electron luminosity of ≈ 1.2 × 10 cm s. An option has final focus quadrupoles starting immediately after the detector at 4.5 m, instead of at 32 m in the baseline. This allows the use of lower βs. It also uses more, 720, lower intensity, bunches, giving reduced IBS emittance growth and requiring only low energy pre-cooling. It has a peak luminosity of ≈ 7 × 10 cm s. An upgrade of this option, requiring magnetic, or coherent, electron cooling, has 1440 bunches and peak luminosity of ≈ 15 × 10 cm s.

Recent developments on the muon Non-Scaling FFAG for the Neutrino Factory and its subsystems

The current status and recent developments on the muon non-scaling FFAG for the Neutrino Factory studied in the framework of the EUROnu/IDS-NF projects are presented. Beam dynamics studies, including the process of acceleration, are discussed. A first pass at engineering for the layout of the ring cell is described. Progress of studies on the main machine subsystems is discussed. The future plans for the study are described.