Perspectives of Electron Cyclotron Resonance Ion Sources Beyond the Scaling Laws

Electron cyclotron resonance ion sources (ECRIS) are the most efficient ion sources among those used in facilities for nuclear physics with stable and exotic beams, because of their ability to generate intense beams of medium charge state ions, or moderate intensities at high and very high state of charge (hundreds of eμA of U33+o Xe34+). Their development has been based primarily on semi-empirical laws (High-B mode plus frequency scaling), which link the performances in terms of current and produced charge state distribution to the magnetic field (that provides the ion confinement in the plasma) and to the frequency of microwaves (used for plasma heating). A further scaling in field and frequency, to access larger extracted current and charge states, involves a considerable impact on the ion sources complexity and cost, probably exceeding the technological limits for superconducting magnets. The experience gained in the last decade produced an understanding of some new mechanisms of plasma production in ECRIS, highlighting the main weaknesses of the previous model. Additional requirements such as the improvement of stability and reliability or the minimization of beam-current ripple require a perfect knowledge of the plasma heating mechanism, to be obtained via experimental and theoretical work, accompanied by adequate plasma and beam diagnostics. We will review hereinafter the basis of the so-called “standard model” for ECRIS beam production along with the new ideas that in the coming years may disclose the path towards further improvements.