Abstract
The concept of a fixed field alternating gradient (FFAG) accelerator was
invented in the 1950s. Although many studies were carried out up to the late
1960s, there has been relatively little progress until recently, when it
received widespread attention as a type of accelerator suitable for very fast
acceleration and for generating high-power beams. In this paper, we describe
the principles and design procedure of a FFAG accelerator.
1 Introduction
The idea of a fixed field alternating gradient (FFAG) accelerator is not new. It was invented in the
1950s right after the alternating gradient (AG) synchrotron came out [1, 2]. Instead of using pulsed
magnets as in a synchrotron, FFAG accelerators use constant field magnets like cyclotrons. Unlike
cyclotrons, however, FFAGs rely on AG focusing so that the beam size can be much smaller. In the
literature [1], there are accelerators described as FFAG betatrons, FFAG cyclotrons and FFAG
synchrotrons. This is a little confusing and in these cases, FFAG refers merely to the focusing scheme
based on so-called cardinal conditions, which we discuss later. Here we use the terms “FFAG
accelerator” or “FFAG” to mean accelerators using the FFAG focusing scheme.