MPM Optimization for Improved Thermal Management

A new generation of microwave power module (MPM) has been developed by THALES. The product line has been optimized for improved thermal management by employing enhanced simulation methods. The primary source of heat within the MPM is the collector of the TWT. The TWT collector was modeled using a ray optics code to determine its thermal dissipation profile with improved accuracy. The thermal dissipation profile was determined for multiple operating points across the frequency band from small signal up to saturation. The total thermal dissipation is calculated for each electrode within the collector by summing the heat contribution from each ray that `lands' on a given electrode. In the case of a three-stage collector, up to three heat sources were defined depending on the operating mode of the TWT. Without RF drive, all the beam current is collected on the third collector electrode, thus all the heat is concentrated on this electrode and a single heat source is an acceptable approximation. With increased RF drive, the beam current is redistributed to each of the three collector electrodes, thus three heat sources are defined. A three-dimensional, finite-element model was constructed, which included the metalized collector ceramic, the collector cooling block assembly, and the MPM baseplate assembly. A thermal analysis was performed on the finite-element model using the multiple heat source distributions derived from the ray optics simulations of the TWT collector. The heat sources were defined along the metalized portions of the collector ceramic.