Design and testing of ceramic breaks for the electrostatic residual ion dump of the ITER neutral beam test facility

The operating principle of the ITER heating neutral beam injector ( is based on the acceleration and neutralisation of negative ions . The remaining charged particles after the neutralization process shall be removed by an e lectrostatic residual ion d ump (ERID) in which electrostatic fields are used to deflect the ions that are so dumped onto five water actively cooled p anels delimiting the four channels particle beam In order to realize the electrostatic field, three panels are grounded and the other two are polarised at a negative potential up to 25 kV The electric insulation on cooling pipes between polarised panels and ground is realized by ceramic breaks with 145 mm outer diameter and made of explosion bonded 316L tutanium grade 2 plates that are brazed to an alumina type IV tube ( titanium grade 2 side) and welded to cooling pipes (316L side)side). Alumina ha s excellen t thermal stability, oxidation and corrosion resistance . On the other hand, titanium grade 2 ha s good ductility besides the high strength and l imited mismatch of the coefficient of thermal expansion with respect to alumina . Nevertheless, large residual stress es are expected in the brazed joint due to the wide temperature range between solidus temperature (780 °C) of the brazing alloy ( Ticusil® and room temperature Different brazed joint configurations were analyses by means of finite element analysis (FE A)A), by modifying the geometry and the position of the braz ed joint . The involved materials were simulated by bi linear model s of the stress strain curve and with n on linear temperature dependence of thermal expansion coefficients Influence of a 50 µm thic k interlayer made of Ticusil® between alumina and titanium was also simulated in order to reduce the stresses Von Mises criterion was selected to evaluate the st r ess field in the metallic parts while Drucker Prager criterion was implemented to assess the strength of the alumina tube.