Coherent electron cooling and two stream instabilities due to electron cooling

This thesis deals with beam dynamics issues associated with electron cooling of an ion beam in a storage ring. In the presence of electron cooling, various effects could happen to the circulating ion beam other than the desired incoherent cooling due to scattering. Firstly, the long-range Coulomb's interaction between the ions and electrons can coherently stabilize or destabilize the ion beam depending on certain cooling schemes. Secondly, as a result of cooling, the momentum spread could be reduced too much such that the Landau damping cease to stabilize the beam and cause the so-called 'over-cooling'. Finally, the coherent effects of the electron beam can serve as a mechanism for stochastic cooling. Under certain circumstance, the coherent electron cooling rate can be much higher than what is due to scattering.;The coherent instabilities of monopole, dipole and quadruple type were studied and their thresholds as well as growth rates are given. For magnetized electron cooling scheme, the ion clouds accumulation was studied and their effects on the two stream instabilities were calculated for the RHIC parameters. A simulation code, TRANFT, was used to track the ion beam in presence of the electron coherent force and coupling impedance of the accelerator. The instability threshold for the energy spread and the bunch population was found from the simulation and compared with the theoretical estimate.;Beyond the stability issues, the long range Coulomb force from the electron beam can also be used to cool the ion beam which brings the new concept of cooling, the coherent electron cooling. The basic concept of the coherent electron cooling is introduced and the dynamics of the first process, the modulation process, and the second process, the FEL amplification process, have been studied in detail. It is shown that analytic formula can be derived to estimate the electron response to a moving ion under certain assumptions and the FEL amplification process can be analytically described by 1D FEL theory. For more general cases of the modulation process, the numerical calculation is also presented.