The thermal behavior of the ring-plane TWT in the interaction area was analyzed by means of the thermodynamic method.The geometric factor

which describes the thermal resistance of the structure for constant thermal conductivity

was defined by solving the heat conduction equation.Starting from the definition of the geometric factor and taking the interface heat resistance into account approximately

the actual temperature rising of all assemblies of the TWT was calculated under the case of that the thermal conductivity varies with the temperature.Making use of the numerical results

the maximum temperature was also given in this paper.The influences of the thermal and geometrical parameters on the heat behavior were discussed.The results presented here are beneficial to the design of the ring-plane TWT.