Analysis and design of a traveling wave tube feedthrough

Results are presented of an investigation aimed at understanding the critical parameters that cause surface breakdown of a high-vacuum feedthrough insulator used in traveling-wave tubes (TWTs). Further impetus was the need to design a feedthrough with a higher hold-off voltage compared to existing designs so as to increase the reliability of TWT operation. Improvement in voltage hold-off was accomplished by fundamental electric field analysis and sound engineering practice. The electric stress enhancement at the insulator/flange interface was the source of flashover initiation. It was found that the hold-off voltage was greatly improved if the flange met the insulator at a right angle rather than an acute angle. The influence of various device operational parameters and physical constraints imposed by the geometry of the TWT were also investigated. A combination of spot welding and cathode termination leading to high stress enhancement led to the lowest breakdown voltages among the factors studied here. Practical means of ameliorating the premature insulator failure are presented.<
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