A 3D kinetic study of the plasma relaxation processes caused by the propagation of an electron beam in high-temperature plasma was carried out. The mathematical model is built on the basis of the Particle-in-Cell (PIC) method. The performance for supercomputers powered by both Intel Xeon processors and Nvidia Tesla GPUs (Graphic Processor Units) is given. It is shown that the particle motion stage is computed much faster with Tesla. Also, the optimization techniques are given for the PIC simulation with GPUs.