Brazing Failure Analysis in Single-Insulator Multi-stage Depressed Collector of TWTs

Travelling wave tubes (TWTs) are generally known for their broadband operation, high gain and high efficiency of ~60%. Typically for efficiency enhancement of the TWTs, multi-stage depressed collector (MDC) with multiple stages of depression are used. Although different technologies exist for collector development, singleinsulator MDC (SI-MDC) outperforms others in providing (i) high breakdown limits, (ii) reduced size and size, and (iii) simple fabrication. But, the major challenge in these SI-MDCs has been in achieving the hermetic braze joints. The SI-MDCs had been developing micro-leaks immediately after brazing operation. Here, in this work, the authors have performed multiphysics ANSYS simulations to systematically understand the root cause of failure occurring during the brazing operation of SI-MDC assemblies. Correspondingly, the authors have modified the feedthrough connections to eliminate the excessive stress developing at the feedthrough pins, which was identified to be the root cause. The modified SI-MDC hasresulted in hermetic brazing joints validating the failure analysis. The detailed description about the simulation studies carried out to emulate the brazing process and their corresponding results are presented.