Comparison of operations of the SERSE ion source at 18 and 28 GHz

The SERSE source has been efficiently working at the Laboratori Nazionali del Sud in Catania since 1998, by operating at 14 and 18 GHz, with a maximum power of about 2 kW, for the beam injection into the K-800 Superconducting Cyclotron. In 2000 a collaboration was established in order to test the behaviour of SERSE at 28 GHz, so that a new operating domain could be studied, featuring a very dense plasma (up to 10¹³ cm^-3) and hopefully a very high current of highly charged ions (I emA of Pb²⁷⁺ is the goal of CERN and GSI for future heavy ion projects). Tests were carried out with a generator based on a gyrotron tube which was refurbished and made available by CEA and Xe ions were chosen as a reference, because the ionisation difficulty for Xe²⁰⁺ is similar to Pb²⁷⁺. The results were excellent and the current of Xe²⁰⁺ exceeded our expectations (more than 0.5 emA in afterglow and more than 0.35 emA in dc mode). These results, obtained with a limited power (4 kW in dc mode and 6.5 kW in pulsed mode), can be considered as a remarkable step, in view of the third generation of ECR ion sources. The details of the experiments will be described, along with the comparison of the results obtained with the injection of 18 GHz microwave