X-ray diagnostics of ECR ion sources-Techniques, results, and challenges.

The high magnetic confinement provided by the minimum-B structure of electron cyclotron resonance ion sources (ECRIS) hosts a non-equilibrium plasma, composed of cold multi-charged ions and hot electrons whose energy can expand up to ≈1 MeV. With a very limited accessibility, the ECR plasma is difficult to study. The x-ray photons generated by the interaction of the warm and hot electron populations within the plasma, as well as the photons generated by electrons lost to the chamber wall, are a signal of great interest as it gives an insight to the properties of the ECR plasma. After an introduction presenting the mechanism generating the x rays in ECRIS, this Review presents the methodology to measure x rays both for volumetric measurements and plasma imaging. The main insights of those measurements are presented. Prospects of x-ray measurements to better understand the plasma dynamics are finally highlighted.