Abstract
In this paper, we investigate the stability of the particle trajectories in Fixed Field alternating gradient Accelerators (FFA) in the presence of field errors: The emphasis is on the scaling radial sector FFA type: a collaboration work is on-going in view of better understanding the properties of the 150 MeV scaling FFA at KURRI in Japan, and progress towards high intensity operation. Analysis of certain types of field imperfections revealed some interesting features about this machine that explain some of the experimental results and generalize the concept of a scaling FFA to a non-scaling one for which the tune variations obey a well defined law. A compensation scheme of tune variations in imperfect scaling FFAs is presented. This is the cornerstone of a novel concept of a non-linear non-scaling radial sector fixed tune FFA that we present and discuss in details in the last part of this paper.
Highlights
The scaling fixed field alternating gradient accelerator (FFA) is a concept that was invented in the 1950s almost independently in the United States, Japan, and USSR [1,2,3]
This is achieved by introducing an Rk increase of the magnetic field with the radius, resulting in the beam experiencing the same focusing throughout the acceleration, keeping the tunes constant
For the case of a radial sector FFA, the flutter function is independent of the radius, and the expression of the magnetic field seen by the particle is written as a function of the azimuthal angle: B1⁄2RðθÞ; θ 1⁄4 Bm1⁄2RðθÞFðθÞ: ð40Þ
Summary
The scaling fixed field alternating gradient accelerator (FFA) is a concept that was invented in the 1950s almost independently in the United States, Japan, and USSR [1,2,3]. A large dynamic acceptance can be achieved, since the crossing of the betatron resonances is avoided in this concept This is achieved by introducing an Rk increase of the magnetic field with the radius, resulting in the beam experiencing the same focusing throughout the acceleration, keeping the tunes constant. Due to the complexity of the field profile and flutter of the magnets, field imperfections can be problematic and difficult to cure, since the orbits move outward from the center of the machine with increasing energies This can lead to the crossing of several betatron resonances at low speed and to beam deterioration in consequence. The details of the measurement as well as the methods and tools that were used to characterize the 150 MeV KURNS FFA are discussed in Ref. [7]
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