A fast tracking code for evaluating collective effects in linear accelerators

Abstract

dition, operation at cryogenic temperatures reduces the breakdown rate probability in rf cavities [15,16] which allows to achieve higher accelerating gradients also in the main linac. Moreover, a recent design concept proposed by SLAC, known as distributed coupling, allows a further enhancement of the accelerating gradient [17,18]. Such a technique exploits waveguide manifolds to feed the rf power individually in each cell of periodic structures. As a result, the iris dimensions are no longer constrained to coupling requirements and the individual cell shape can be optimized to maximize the acceleration process. This clever concept has been embraced for the realization of cutting edge facilities based on C-band linacs such as ultra-compact X-ray FELs [19], low bandwidth and high flux ICS machines [13,14] and linear colliders [20,21].The above features combined together define a unique scenario for the beam dynamics of high brightness electrons for the following reasons.• The high accelerating gradient and the rich content of space harmonics arising from the optimized cavity topology have a strong impact on the transverse optics [22,23]. As we will discuss in the next section, such features make possible to provide radial focusing in booster linacs following the gun without