Electrical insulation of plasma facing metallic structures for the RFX-mod2 experiment

This paper discusses the electrical insulation of a copper structure, which will be installed in the RFX-mod2 machine, in the presence of a weakly ionized plasma. The effectiveness of aluminum oxide (alumina) coating in preventing electrical discharges was evaluated through tests conducted both in air and in a weakly ionized plasma environment. It was shown that copper samples with alumina surface deposition sustained a voltage of about 2 kV in air but showed dielectric breakdown in the presence of plasma. SEM analysis revealed an irregular microstructure with a high degree of porosity and large internal cavities, which tend to reduce the effective coating thickness. New copper prototypes with more compact and less porous alumina deposition showed effective electrical insulation in the presence of plasma, highlighting how porosity and compactness are important factors in ensuring electrical insulation in the presence of plasma. The use of other materials, such as paints, silicones and resins, to insulate the inner part of holes in the copper structure, due to limitations in applying alumina coatings with plasma spray techniques, is also discussed.