In the design of a linac such as the 4 MeV linac fabricated at SAMEER, simulation of electron beam dynamics plays an important role. We study electron beam dynamics to help in design of buncher cavity dimensions, linac length and effect of beam loading on electron energy and spectrum. We have written a program to calculate the electron trajectories for a given power input, with cavity dimensions, rf couplings and electron beam input voltage and current as parameters. By calculating the trajectories of electrons arriving at different rf phases, we get the average electron energy, percent of beam transmitted and electron energy spectrum. By running the program with different input parameters, we can choose the best combination for a required application such as
radiography or cancer therapy
