Never Run Your ECR Ion Source with Argon in Afterglow for 6 Months!

The fixed target experiment NA61 in the North Area of the SPS at CERN studies phase transitions in strongly interacting matter using the primary beams available from the CERN accelerator complex (protons and lead ions). In order to explore a wider range of energies and densities a primary argon beam was requested for the physics run in 2015. The GTS-LHC ECR ion source was running for many months during 2013 and 2014 to study the source behaviour and to setup the accelerator chain with argon ions. This paper reports the long term effects of the argon operation on the GTS-LHC ion source and the Low Energy Beam Transport (LEBT). Heavy sputtering inside the source caused a degradation of the plasma chamber and metal coating of insulators inside the beam extraction system. Iron ions could be found in the extracted beam. Also the pumping performance of ion getter pumps in the LEBT degraded significantly. Additional preventive maintenance was necessary to be able to run for long periods without risking serious damage to the ion source.