Prediction of thermal contact resistances and temperature distribution at different joints in helix traveling-wave tubes

Improper fitting of helix bundle to rod and rod to barren envelope leads to high thermal resistances and hence restricts average power handling capability of a TWT. In this paper, authors have calculated thermal resistances at different joints of a helix traveling-wave tube (TWT), analytically and validated with COSMOS software.

Introduction

Heat dissipation, in helix traveling-wave tubes (TWTs) restricts average rf power handling capability, also affects stability and reliability of TWT. In conventional TWTs, helix slow-wave structure (SWS) is supported by dielectric supports in metal enclose (Fig. 1). Proper fitting of helix-support rod bundle in the metal envelope reduces thermal resistances at the helix to rod and rod to metal envelope. Moreover, due to periodicity of helix SWS, helix to support rod contact is discrete rather than continuous and which is reverse in rod to metal envelope contact. Roughness of different surfaces reduces contact areas for heat dissipation and leads to enhanced thermal resistances.