Venturini Delsolaro, W. Miyazaki, A. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-194-6 10.18429/JACoW-LINAC2018-TU1A05 English 292-296 TU1A05 cavity ISOL niobium linac cryomodule Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-LINAC2018-TU1A05 http://jacow.org/linac2018/papers/tu1a05.pdf The HIE-ISOLDE post accelerator consists of 4 cryomodules with 5 niobium-coated Quarter Wave Reso-nators (QWR) each. The standard manufacturing tech-nique was to machine the inner and outer conductor sepa-rately, to shrink-fit the 2 pieces and to apply an electron beam welding at the interface. Due toμcracks, ob-served on some of the cavities around the welds, we took the decision to explore the possibility of a seamless de-sign. First cavities became available in late 2017 and were then cold-tested in the vertical cryostat. These seam-less coated quarter wave resonators have shown some of the highest Q-values of all HIE-ISOLDE cavities in the acceptance tests. Furthermore, we studied the cavity per-formance with different compensations of the earth mag-netic field and different temperature gradients upon cool down. These tests have demonstrated record-breaking RF surface fields for the Nb/Cu technology. This paper re-views the design and fabrication and reports on the cold tests results of seamless quarter wave resonators, and of possible future applications