Application of Ferroelectric Cathodes to Enhance the Ion Yield in the Caesar Source at LNS

With increasing RF power the electron concentration in the plasma of ECR ion sources is decreasing in comparison to the ion concentration, so that the plasma is charging up positively. Direct injection of electrons into the ECR plasma can increase the electron charge density and the ion current yield. We have used ferroelectric cathodes to inject electrons into the Argon plasma of the CAESAR ion source at INFN-LNS (Catania, Italy). The cathode was placed at about 10 cm from the hot plasma and a bipolar high voltage pulse of 1.6 kV was used to trigger the electron emission. No additional acceleration has been provided. The use of the ferroelectric cathode leads to an increase of about 30% of the Ar8+ intensity, which has been monitored during the test. In addition, magneto-hydrodynamic instabilities in the ECR source were damped during and after electron injection.