The mesh PM for the AMS Time Of Flight, comparison between simulation and measurements

A simulation of fine mesh photomultipliers (PM) has been performed in order to understand their behavior in a magnetic field, in view of their use in the Time Of Flight system of the AMS-02 experiment, which is a cosmic ray spectrometer to be operated in space after 2006. The model on which the phototube simulation is based is described and a comparison with the experimental data are given. The simulation results can account for the apparent fine mesh low gain and bad single photoelectron resolution. The time response of a fine mesh in a magnetic field has been investigated with the use of the Monte Carlo, which also turned out to be a useful tool in understanding the change of PM gain as a function of the angle between the magnetic field and the PM axis. All the Monte Carlo results agree quite well with the data taken.