Anti-multipactor TiN coating of RF power coupler components for TESLA at DESY

A development project was carried out at DESY, aimed at reducing secondary electron emission and multipactor effects in TESLA couplers by TiN layers generation on surfaces which were not protected in this way previously. Thin TiN films on ceramic or metallic surfaces were produced by deposition from Ti vapor in low pressure ammonia. Selection of processing parameters and their effect on multipactor suppression in RF field have been studied using a multipactor test resonator at DESY. Appropriate values of deposition rate, substrate temperature, final layer tickness and chemical conversion procedure were selected. A significant reduction of multipactor time during RF tests was reached due to surface coating. Chemical analysis of TiN layers on both ceramic and metallic substrates has been performed using SIMS method. TiN coating of more than 80 waveguide and cylindrical RF windows were done for TTF2, TTF3 and TTF4 versions of TESLA couplers. Surface processing of flat waveguide windows for TTF2 resulted in significant reduction of multipactor effects and improvement of power transmission. Their good performance remained unchanged after 24-hour exposition to air. TiN coating of all vacuum-facing surfaces of a TTF2 coupler led to reduction of the indispensable RF conditioning time at a pulse length of 20 μs from typically 3 days down to 4.5 hours. The above activities are considered a preparatory step for the future large-scale anti-multipactor protective coating of TESLA couplers. TESLA Report 2004-02