Characterization of the versatile ion source and possible applications as injector for future projects.

The versatile ion source (VIS) is an off-resonance microwave discharge ion source which generates a slightly overdense plasma (n(e) ≈ 10(17) cm(-3)) operating at 2.45 GHz and producing more than 50 mA of proton beams. A detailed characterization of the source, by operating between 60 and 75 kV, in terms of emittance, current extracted and proton fraction is reported below. Moreover, passive techniques (alumina coating of the plasma chamber walls, BN disks at the injection and extraction endplates) have been used to improve the performance of the source, increasing the electron density for a more efficient ionization. The know-how achieved with the VIS source may be useful for the different project, particularly for the European spallation source.

Modification of anisotropic plasma diffusion via auxiliary electrons emitted by a carbon nanotubes-based electron gun in an electron cyclotron resonance ion source.

The diffusion mechanism in magnetized plasmas is a largely debated issue. A short circuit model was proposed by Simon, assuming fluxes of lost particles along the axial (electrons) and radial (ions) directions which can be compensated, to preserve the quasi-neutrality, by currents flowing throughout the conducting plasma chamber walls. We hereby propose a new method to modify Simon's currents via electrons injected by a carbon nanotubes-based electron gun. We found this improves the source performances, increasing the output current for several charge states. The method is especially sensitive to the pumping frequency. Output currents for given charge states, at different auxiliary electron currents, will be reported in the paper and the influence of the frequency tuning on the compensation mechanism will be discussed.

Comparison between off-resonance and electron Bernstein waves heating regime in a microwave discharge ion source.

A microwave discharge ion source (MDIS) operating at the Laboratori Nazionali del Sud of INFN, Catania has been used to compare the traditional electron cyclotron resonance (ECR) heating with an innovative mechanisms of plasma ignition based on the electrostatic Bernstein waves (EBW). EBW are obtained via the inner plasma electromagnetic-to-electrostatic wave conversion and they are absorbed by the plasma at cyclotron resonance harmonics. The heating of plasma by means of EBW at particular frequencies enabled us to reach densities much larger than the cutoff ones. Evidences of EBW generation and absorption together with X-ray emissions due to high energy electrons will be shown. A characterization of the discharge heating process in MDISs as a generalization of the ECR heating mechanism by means of ray tracing will be shown in order to highlight the fundamental physical differences between ECR and EBW heating.