Thermal Analysis of a Helix TWT Slow-Wave Structure
ABSTRACT A novel and effective analytical method using ANSYS has been developed for studying the heat-dissipation capability of a helix traveling-wave-tube slow-wave structure (SWS). This method, which is based on calibrating theoretical calculations with experimental data, is able to precisely predict the SWS heat dissipation, thereby reducing material costs and saving time. The consistency and feasibility of this method have been verified by experimental tests on SWSs using copper-plated helices and both BeO and BN support rods.
- [show abstract] [hide abstract]
ABSTRACT: Finite element analysis (FEA) techniques were used to assess the mechanical performance due to thermal loading of a high power, wide band, helix traveling wave tube's interaction (slow wave) circuit. A steady state heat transfer analysis was performed using calculated heat dissipations and boundary temperatures that were obtained through data supplied by the TWT's manufacturer. The resulting temperatures from this analysis were used as loading conditions in a linear static analysis of a smaller model which represents a 12 turn section of the circuit. The failure modes investigated were cracking of the helix tape and fracture of the support rods due to excessive thermal stresses. Cracking of the helix tape would cause an open-circuit to occur while fracture of the support rods could cause small mechanical perturbations in the slow wave structure which may reflect the RF signal. Both cases could possibly lead to electrical failure of the TWT. Static stress analysis of the attenuation section indicated that the stress levels in the helix and support rods due to this particular temperature gradient were within acceptable limits and would not fracture if these components were free of initial cracks or flaws. Stresses through the helix were sufficient to nucleate cracks, however the length of these cracks would be minute and would not affect the useful life of the helixAerospace and Electronics Conference, 1993. NAECON 1993., Proceedings of the IEEE 1993 National; 06/1993
Conference Proceeding: Thermal properties and power capability of helix structures for millimeter waves[show abstract] [hide abstract]
ABSTRACT: The thermal properties of materials, that can be used for high power helix structures, were evaluated experimentally with equipment that incorporated an infrared microscope for temperature measurements. The interface heat transfer properties between such materials were measured as a function of contact pressure and for different surface finishes. In addition the thermal conductivity of suitable ceramic materials, such as anisotropic Boron Nitride, Beryllia and Diamond was measured as a function of temperature. Millimeter wave helix structures for 40 GHz to 50 GHz were constructed for thermal evaluation with these materials. The Diamond supported helix structure demonstrated a power handling capability of 165 Watts/in with an average helix temperature of 380°C, indicating that helix traveling wave tubes can be designed for power levels of 100 Watt to 200 Watt CW in the 40 GHz to 50 GHz range using such a structure.Electron Devices Meeting, 1978 International; 02/1978
Conference Proceeding: Predicting thermal contact resistance in circuit card assemblies[show abstract] [hide abstract]
ABSTRACT: On a typical conduction-cooled Circuit Card Assembly (CCA) there is a temperature rise caused by the resistance between component die, Printed Circuit Board (PCB), thermal frame (heat sink), and chassis. While the resistance at the component junction, through the PCB, and through the thermal frame can be readily calculated from material properties, modeling the thermal frame and card clamp to chassis interface can be difficult. For CCA power below approximately 25 watts the loss at the interface is usually less than 4°C (0.30°C/W for bare aluminum). As the thermal dissipation on a CCA reaches 50-75 watts (>1 watt/in<sup>2</sup> on VME 1101.2 format), it becomes necessary to model this interface because of its increasing influence on the overall temperature rise. A method utilizing several Unigraphics GRLP routines, SINDA thermal analysis software, and empirical data has been developed that predicts the thermal interface performance between both the chassis and thermal frame, and the chassis and card clamp to within 30 percent of measured valuesThermal Phenomena in Electronic Systems, 1994. I-THERM IV. 'Concurrent Engineering and Thermal Phenomena'., InterSociety Conference on; 06/1994