Brazing of large-diameter ceramic rings to niobium using an active metal ticusil process

A Heavy Ion Injector Program is in progress at Los Alamos National Laboratory to develop an ion injector for the initial phase of the Heavy Ion Fusion Program. The basic design incorporates a 2 MeV Marx generator cantilevered inside one end of the pressure vessel. The accelerating column is cantilevered from the opposite end with the HV domes located between the generator and the accelerating column. A 15 kVA motor-driven alternator and transformer is located inside the HV domes with other electrical equipment used to power the sixteen ion beam sources located at the 2 MV end of the column. The accelerating column is made up of two 18.6 in. (472 mm) long ceramic/niobium modules brazed under vacuum and bolted together. The ceramic chosen was Coors AD-85 (85% alumina), since this was the highestalumina-content ceramic ring that could be pressed in the 28 in. (710 mm) OD size required. The thermal expansion curves of niobium and AD-85 match very closely, as shown in Fig. 2, thus helping to minimize residual thermal stress due to the braze cooldown cycle.