Role of a metal–dielectric structure for the high-charge-state-ion production in electron cyclotron resonance ion sources

Abstract

The influence of a metal–dielectric (MD) cylindrical structure, covering the radial walls of the plasma chamber of an electron cyclotron resonance ion source (ECRIS), on the production of highly charged ions is discussed. Its influence on the main plasma parameters (plasma potential, electron density, and electron temperatures) was investigated using the Langmuir probe method. An increase of these parameters was observed when the MD structure was inserted into the plasma chamber of the Frankfurt 14 GHz ECRIS. In addition, the plasma potential was measured independently by determining the offset extraction voltage at zero magnetic field of the magnetic 90° analyzer field with high precision. Good agreement with the Langmuir probe results was obtained. The main influence of the MD structure is characterized by a significant increase of the plasma potential. This indicates that the MD structure helps to increase lifetimes of both, electrons as well as ions. The ion lifetime is known to be one of the essential parameters to influence the production of highly charged ions.