User Guide for Wake

WAKE is a code simulating multi-bunch, multi-particle beams in linac with wakefields having high group velocity. The group velocity complicates the calculation because of the constant relocation of the particles creating the field and because the path length of a particle within the field of a preceding particle is not the length of the RF structure, but depends on the distance between the particles. It is the potential, i.e. the product of the field and the path length which is considered, rather than the field itself. In order to account for the varying positions of the particles, the structure is divided into intervals at the end of which the potentials are calculated. To save time, summing the potentials is not repeated, but the vector sum is transformed by the difference in phase when a particle replaces the preceding one at the same section end. A complementary update is necessary because the transverse positions have changed. The equations of the dynamics are then applied. In addition to this specific treatment for the wakefields, more conventional operators for travelling wave acceleration and focusing are provided. The focusing forces may be automatically adjusted for a decelerator or given at each focusing element. The input list is simple and one can select output graphics representing the results of the longitudinal and the transverse motions for the whole beam train, or for groups of particles. The code, written in FORTRAN 77, is the result of years of studies of the CLIC decelerator and of the CTF accelerator and decelerator. It has been tested against experimental measurements in CTF. Examples are given for these machines.