Development and commissioning of the ion implanter for the HOLMES experiment

The HOLMES experiment aims to directly measure the ν mass studying the 163Ho electron capture decay spectrum, using arrays of TES-based micro-calorimeters implanted with O(102 Bq/detector) 163Ho atoms. The neutron irradiation of 162Er enriched samples, used for the production of 163Ho, also generates radioactive contaminants. Chemical processes have been developed to extract the Ho fraction with high efficiency. The radioactive Ho isotope 166mHo is also present in the final sample and could significantly contribute to background events in the final spectrum. For this reason a dedicated implantation/mass separator has been set up and commissioned. It is designed to achieve more than 5 σ separation 163/166 u simultaneously allowing an efficient 163Ho atoms embedding inside micro-calorimeter absorbers. Its main components are a 50 kV sputter-based ion source, a magnetic dipole and a target chamber. A specially designed co-evaporation system has been implemented to deposit gold on the detector absorbers during implantation to overcome the 163Ho source saturation problem. The system performances in terms of achievable beam current, profile and mass separation have been evaluated by means of calibration runs using Cu, Mo, Au and 165Ho beams. An intensive study was done to optimize the target containing 163Ho in order to achieve a large fraction of ionized Ho in the beam. In this work, the machine development and commissioning will be described.