Investigation of particle dynamics in ECR Ion Source plasmas(~*)

摘要

The Electron Cyclotron Resonance Ion Sources (ECRIS) are nowadays the most effective devices that can feed the particle accelerators in a continuous and reliable way, providing high current beams of low and medium charge state ions and relatively intense currents for highly charged ions. ECRIS are on the one hand important tools for research with ion beams (in surface, atomic and nuclear science);on the other hand, they imply plasma under extreme conditions and constitute thus themselves objects of scientific interest. A detailed investigation of the particle dynamics in ECRIS plasmas is here presented: electron heating and confinement are studied numerically, and the results are then compared with experimental results.Some variations to the classical ECR-heating mechanism are proposed: the frequency tuning effect and the two-frequency heating in particular, but details about the effects of particular phase relationships in multi-wave plasma heating are also given. A special attention was paid to the electron heating until extremely high energies: this is a key issue for the safety of future, high performances sources, as these hot electrons are useless for ionizations and detrimental for the helium cryostat surrounding the superconducting coils of the magnetic system. Radically different heating schemes are also proposed, as the Bernstein wave heating currently under investigation for fusion devices. The influence of the electron dynamics on the ion beam emittance has been finally analyzed, in order to maximize the beam brightness and to avoid the formation of halos.