HIE-ISOLDE cavity production – results from thermal modelling of the cavity during sputtering

The HIE-ISOLDE project is in the phase of cavity production and optimization. Cavities are made of copper and sputtered niobium. We build an ANSYS model to model thermal distributions and heat flows in the cavity structure. We limited the analysis to handle the cavity during sputtering and investigated the effect of different coating power. The aim was to check how results compare to experimental data and vary boundary conditions to improve the model. With two boundary conditions (fixed room and cavity top temperatures), we observed a power loss due to fixed temperature, as expected. The temperature gradient between the bottom and top cavity did not reach the values of the experimental data. With one boundary condition (fixed temperature on sputtering chamber structure), the expected linear proportionality was observed clearly between the temperatures of the cavity and the power. The temperature gradients were also observed to increase with power. We observed an offset in the data compared to experimental data. The actual sputtering conditions could be roughly predicted using the computational data. The fittings could be transformed to match experimental data at some power level by lowering the offset. Also, the temperature gradient between measured points in the actual coatings could be used to tilt the slopes to match experimental data and improve predictions of the model.