Lessons learned from the HIE-Isolde cavity production and cryomodule commissioning

The HIE-ISOLDE superconducting linac started opera- tions at CERN in 2015 with a first cryomodule hosting five superconducting quarter wave resonators (QWR). These cavities are based on the Nb/Cu technology. In time, two more cryomodules have been assembled, installed and commissioned on line, bringing the energy reach for the heaviest ions (A/q=4.5) up to 7.5 MeV/u. In 2017, while the first three cryomodules were prepared for the physics run, six more cavities were produced of which five will be installed in a fourth cryomodule. With this, the high beta section of the linac will be complete and the energy will reach 10 MeV/u for A/q=4.5. In this paper we review the experience and lessons learned during the construction of HIE-ISOLDE, along with some still open questions.