User's guide for ABCI Version 8.8 (azimuthal beam cavity interaction)

ABCI is a computer program which solves the Maxwell equations directly in the time domain when a bunched beam goes through an axi-symmetric structure on or off axis. An arbitrary charge distribution can be defined by the user (default=Gaussian). This document is meant to be a comprehensive user's guide to describe all features of ABCI version 8.8, including also all additions since the release of the guide for version 6.2. The main advances lie in its higher speed of execution, and improved capabilities of Fourier transformations. The impedance and the frequency spectrum of deposited energy can be calculated and plotted from the Fourier transforms of the wake potentials. The ''data windowing'' technique can be applied to wake potentials in order to reduce the undesirable spectral leak-age effect. A number of window functions can be chosen by the user. Numerical values of wake potentials as well as the Fourier transform results can be saved on separate files which can be used directly for other programs. In addition to these additions to the program, a criterion was derived for the numerical stability of the time iteration valid for the case where the longitudinal mesh size is larger than the radial one. If the time step is not fine enough to satisfy this criterion, a warning message will be issued and an appropriate value suggested. A second criterion was found to be required to guarantee the accuracy of the computed wake potentials for structures with (long) tapers. ABCI now also permits a structure with ''islands,'' i.e. areas detached from the main body. An option was added to plot either electric field or total current lines at subsequent time steps for the monopole (m=0) case. ABCI is available as a source code in the CERN IBM VM/CMS system