The excitation of wake waves by a relativistic homogeneous electron bunch passing through cold magnetized plasma at equilibrium is studied for arbitrary values of the ratio of bunch density to plasma density. The analysis is based on the assumption that the magnetic field is sufficiently strong (omega(B) much greater than omega(p), where omega(p) and omega(B) are the electron plasma and cyclotron frequencies respectively). The periodic and nonperiodic solutions for the momentum of plasma electrons inside the bunch are analyzed. It was shown that the presence of strong external magnetic field may increase the amplitude of wake waves and the maximum transformer ratio, the latter being reached at densities of bunch power than that in the absence of magnetic field. The optimum conditions for obtaining the maximum values of the wake field amplitude and of the transformer ratio are found.
The contribution of Coulomb elastic scattering of beam particles on the residual gas to the beam halo development in a linear accelerator is studied. Starting from the basic differential cross section formula giving the probability of a particle to scatter at a given angle, we analyse the behaviour of those few particles which scatter at rather large angles and we estimate their proportion relative to the beam intensity. We present a transport code dedicated to the scattering of a beam on the residual gas, which we validate with an experiment in which the beam is transported through a drift space. We use then our code to simulate the transport of a beam matched to a uniform focusing channel and we show how the collisional halo develops. The code is finally used in order to establish the loss rate per meter in a high intensity linac. This loss rate is compared to the acceptable one.
