Optics Design of Vertical Excursion Fixed-Field Alternating Gradient Accelerators

TL;DR

This paper presents a novel design methodology for vertical excursion fixed-field alternating gradient accelerators, using idealized magnetic fields and coupled optics analysis to optimize parameters and dynamic aperture.

Contribution

It introduces a first-principles calculation of idealized magnetic fields and a new coupled optics analysis tool for designing such accelerators.

Findings

Optics and dynamic aperture depend on key parameters.

Design successfully applied to a 25 m ring accelerating protons from 3 to 12 MeV.

First use of specialized tools for coupled optics analysis in this context.

Abstract

Vertical excursion fixed-field alternating gradient accelerators can be designed with tunes that are invariant with respect to momentum and trajectories that are scaled images of each other displaced only in the vertical direction. This is possible using guiding fields that have a vertical exponential increase, with a skew quadrupole component in the magnet body and a solenoid component at the magnet ends. Because of the coupling this introduces, orbit and optics calculations and optimisation of parameters need to be performed numerically. In this paper, idealised magnetic fields are calculated from first principles, taking into account end fields. The parameter dependence of the optics and the dynamic aperture of the ring are calculated for the example of a ring with an approximately 25 m circumference that accelerates proton beams from 3 MeV to 12 MeV. The paper reports for the first time the design of such an accelerator lattice using tools specifically devised to analyse transverse coupled optics without the need for approximations.