In recent years, considerable progress has been achieved in generating electromagnetic pulses in the centimeter and millimeter wavelength range based on the phenomenon of Cherenkov superradiance (SR) from high current electron bunches [1][2][3]. This pro cess includes self bunching of particles followed by a coherent emission from the entire volume of an extended (on the wavelength scale) electron bunch. The SR pulses are characterized by record high (giga watt) peak power at an ultrashort (subnanosecond) duration.There is a natural trend in these investigations toward the development of SR sources for still shorter wavelengths, including the terahertz range. This can be achieved using the SR from electron bunches mov ing in a periodic magnetic (undulator) field. The energy of these particles should amount to 4-5 MeV at a pulse duration of several picoseconds. At present, the required characteristics can be provided by electron beams generated by photoinjectors [4,5]. Recent investigations of free electron lasers operating in the SR regimes have been mostly concentrated on the case in which the electron bunch length is shorter than or comparable with the radiation wavelength [6][7][8][9]. Under these conditions, coherent emission from the entire bunch volume is possible without self bunching of particles and the undulator length necessary for the formation of a radiation pulse is relatively small. At the same time, it has been demonstrated [10-13] that SR pulses with a much greater peak power can be gener ated using electron bunches extended on the wave length scale. In this case, coherent emission from var ious parts of the bunch is possible due to the develop ment of self bunching. In the general case, this would require an increase in the length of interaction space as compared to the case of a preset motion studied in [6][7][8][9].It should be noted that previous analyses [10][11][12][13] of the undulator SR from extended electron bunches have been performed within the framework of the method of average ponderomotor forces. The present investigation is devoted to numerical simulation of these processes using a particle in cell (PIC) code, which reduces to direct integration of a self consistent system of the Maxwell equations and the equations of motion. Using this approach, it is possible to take into account the relativistic character of electron motion in strong fields, intrinsic electric and magnetic fields of a high current electron bunch, their influence on the particle dynamics, and some other factors inherent in real experiments. However, PIC simulations of elec tron-wave interaction for high energy particles in a laboratory frame of reference require considerable computational resources. Indeed, for a relativistic mass factor of γ 0 ~ 10, the undulator length over which the SR process develops reaches several meters, while the electron bunch length is several millimeters and the radiation wavelength in the terahertz range amounts to fractions of a millimeter.As will be shown below, the simulation pro...