A new 18 GHz room temperature electron cyclotron resonance ion source for highly charged ion beams

An innovative 18 GHz HIISI (Heavy Ion Ion Source Injector) room temperature Electron Cyclotron Resonance (ECR) ion source (ECRIS) has been designed and constructed at the Department of Physics, University of Jyväskylä (JYFL), for the nuclear physics program of the JYFL Accelerator Laboratory. The primary objective of HIISI is to increase the intensities of medium charge states (M/Q ≅ 5) by a factor of 10 in comparison with the JYFL 14 GHz ECRIS and to increase the maximum usable xenon charge state from 35+ to 44+ to serve the space electronics irradiation testing program. HIISI is equipped with a refrigerated permanent magnet hexapole and a noncylindrical plasma chamber to achieve very strong radial magnetic confinement with B_rad = 1.42 T. The commissioning of HIISI began in Fall 2017, and in Spring 2019, it has met the main objectives. As an example, the intensity of the Xe²⁷⁺ ion beam has improved from 20 μA to 230 μA. In addition, the beam intensity of the Xe⁴⁴⁺ ion beam has exceeded the requirement set by the irradiation testing program. The performance of HIISI is comparable to superconducting ECR ion sources with the same maximum microwave frequency of 18 GHz and a total power of 3 kW. For example, Ar¹⁶⁺ and Xe³⁰⁺ ion beam intensities of 130 μA and 106 μA, respectively, have been obtained with a total microwave power of 3 kW distributed between 18, 17.4, and 14.5 GHz frequencies. The ion beams have been extracted through an 8 mm plasma electrode aperture using 15-17 kV extraction voltage. The latest development work, extracted ion beam intensities, special features, and future prospects of HIISI are presented in this paper.