Study of the Bernstein Waves Heating in the WEGA Stellarator Plasma and Possible Applications to ECRIS-ECR Ion Sources

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 multiply charged ions. The heating mechanism of the ECRIS plasma is based on the Electron Cyclotron Resonance, that is able to create multi-keV electrons useful for ionization and to produce a conspicuous number of electrons up to MeV energies, as demonstrated by recent experiments on 3rd generation sources. These electrons are completely useless for the production of highly charged ions (their ionization cross section is very low) and they are also detrimental for the source safety, because they increase the heat load on the superconducting magnets' cryostat, making the magnets operations problematic. With the aim to study alternative plasma heating mechanisms for ECRIS, a series of experimental measurements have been carried out at Max Planck Institute for Plasma Physics of Greifswald, where a Stellarator for nuclear fusion research operates. In the last years it has been demonstrated that the Stellarator plasma can be efficiently heated by means of electrostatic Bernstein waves (BW), generated through an electromagnetic to electrostatic mode conversion mechanism named "OXB-conversion". We will show that a proper BW-heating strongly reduces the number of high energy electrons over a large range of pressure and power. A possible injection scheme for ECRIS-like devices has been designed on this basis and it will be proposed along with a preliminary modelling of the waves to plasma coupling and wave's path and absorption via OXB-conversion in ECR ion sources.