A thermal analysis, which can be implemented on a small computer system, has been developed for PPM (periodic permanent-magnet)-focused rod-supported TWT (traveling-wave tube) helix structures. The method fully accounts for the variable thermal conductivity of several of the materials used in helix assemblies and considers the nonuniform geometry of the various elements of the structure along the direction of heat flow. Including the effects of the thermal interface resistances, accurate predictions can thus be made of the thermal behavior of the circuit for a given power dissipation on the helix, and the influence on the helix temperature rise of the thermal and geometrical parameters of the various elements of the structure can be easily examined. An experimental test shows good agreement with the computed results and indicates that the method can be used to estimate the thermal interface resistance of experimental helix assemblies.
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