Linear non-scaling FFAGs (Fixed-Field Alternating Gradient accelerators) are
machines that use linear magnets to achieve an extremely large energy
acceptance (generally a factor of 2 or more).  This paper examines the
longitudinal dynamics in such a machine, focusing on the longitudinal
acceptance, the phase space area that is transmitted without excessive
distortion.  The paper shows how to compute the distortion in two ways:
computing the emittance growth, and computing the distortion of an initial
ellipse from an elliptical shape.  The paper will describe a model for the
longitudinal dynamics in a linear non-scaling FFAG, show how to compute the
longitudinal distortion in such a machine using a Dragt-Finn factorization,
examine the accuracy of the calculation, and describe how longitudinal
acceptance can interact with other performance criteria for an FFAG.

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Posted by J. Scott Berg