Simulation of thermal energy transport in complicated structures is usually a challenge. An example of such problem is heat generation and transfer through microwave delay structure in the travelling wave tube (TWT) device. A high level of microwave power and considerable energy of electrons intercepted by the delay line leads to the increase of local temperature of the microwave structure. Determination of the heat transfer from the hot spots is essential for the proper design of the delay line and assisting cooling system. This problem has been investigated by means of a combined: analytical, numerical and experimental approach. Such methodology does not require expensive equipment and is much faster than the pure experimental analysis. Presented analytical model is focused on evaluation of the electron beam power dissipation and microwave losses along the delay line, which is not uniform and most of the power is dissipated at terminal part of the delay line. The analytically evaluated power dissipation was used in numerical simulation in order to assess the temperature distribution. Finally the results were validated experimentally using a designed measuring setup. One of the final conclusions was that the temperature distribution has a nonuniform character and the resulting high temperatures at the delay line output can significantly influence the device reliability parameters.978-1-4799-9950-7/15/$31.00 ©20 15 IEEE -1 /8 -

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Travelling Wave Tube (TWT) is an electronic vacuum microwave device, which is used as a high power microwave amplifier, mainly in telecommunication purposes and radar systems. TWT's seem to be an alternative and a more reliable solution than semiconductor devices when building high power and high frequency applications. Thermal behaviour of TWT is one of the key aspects influencing its reliability and working parameters. In fact, the standard TWT is treated as a high power device and the supplied power is dissipated mainly through conduction and convection phenomena. In practical applications, depending on a type of TWT, they can be cooled either by a forced liquid or air circulation. The main goal of the presented research was to perform analytical, experimental and numerical analysis of temperature distribution of a low band TWT in case of a typical working condition. Because theoretical analysis seems to be very complex, thus it was decided to support it with experimental measurements and numerical simulations as well as with the simplified analytical formulas. As a first step of the presented research, the analytical analysis and numerical modelling of the helix TWT was carried out. The objective of the thermal analysis was to assess the temperature distribution in different parts of the helix TWT assembly during extreme standard and working conditions. Afterwards, the obtained numerical results were validated by experimental measurements, which were carried out using a custom designed TWT test sample and corresponding experimental measurement tools.

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The paper describes the design of an C-band microwave unit which consist two-stage preamplifier and a control and diagnostic monitoring system. The main building blocks of this amplifier are: solid state amplifier and helix delay line TWT with proper HV power supply. The necessary input power is ∼5 mW, output power min. 9 kW and duty 5%. The total gain of both stage is 63 dB.