Design and tests for the new CERN-ISOLDE spallation source: an integrated tungsten converter surrounded by an annular UC$_{\chi}$ target operated at 2000 °C

The production of high intensity and isobarically pure neutron-rich fission fragments is of high importance for the physics research program of the ISOLDE facility at CERN. This is typically done in a two-step method where a tungsten converter, positioned parallel and below the UC$_{\chi}$ target, is irradiated with 1.4 GeV protons. This will produce spallation neutrons which irradiate a UC$_{\chi}$ target producing the isotopes of interest. Currently, the in-target production is limited by the geometrical overlap of the neutron fluence and the target material and suffers from low production yield. In this work, a prototype is proposed where the tungsten converter is positioned in the center of an annular UC$_{\chi}$ target. FLUKA simulations were conducted to optimize the geometry, maximizing the production of isobarically pure neutron-rich fission fragments which determined that a large diameter target is necessary (5 cm). Thermo-electric ANSYS$^{®}$ simulations were conducted in order to develop a large Ta target oven which can reach 2000 °C and tests were conducted to benchmark the simulations. A prototype design was validated, for ISOLDE operation, with offline tests which shows that the tungsten-graphite-tantalum assembly is fully stable up to 2200 °C.