Congressional-Microwave Vacuum Electronics Power Res. Ini. TWT Coatings Improvement Investigation

摘要

Gain stability has long been identified as a key attribute for successful long-term operation of both space and terrestrial helix traveling wave tubes (TWTs), whose mission life may extend to 15 or more years. Gain change associated with attenuator (carbon) thin film resistivity change has been observed for at least 30 years; however no definitive experimental evidence to support the various resistance change theories has been available. Using a modified ion source, changes in film resistivity caused by low energy hydrogen ion bombardment of the carbon attenuator have now been positively identified as the cause of gain growth in helix TWTs. Carbon films experimentally damaged by ion bombardment compare identically to those removed from TWTs with thousands of operating hours. An unusual thermal annealing effect seen in TWT films has also been duplicated. Two potential methods to mitigate gain change have also been proposed based on this work.