Radiation resistant alternative substrates for ITER bolometers

The technical feasibility of producing thin substrates from commercially available sheets of alumina, aluminium nitride, silicon nitride, and silicon dioxide by mechanical grinding and polishing has been demonstrated. Thicknesses of about 50 μm with mean surface roughness down to 20 nm have been obtained. Some of these more radiation resistant alternatives to mica for ITER bolometer applications together with CVD diamond have been prepared with gold and platinum ‘U’ shaped 200 nm thick sputtered tracks, and characterized for their I–V behaviour as a function of temperature. Employing such alternatives reduces the problem of substrate lifetime due to radiation induced swelling of mica, as well as increasing the upper temperature limit. In addition used with platinum the transmutation problem associated with gold would be reduced, and the higher platinum resistivity would enable one to use a less delicate meander.