Multiphysics Modeling of High Power Magnetron
The magnetron is one of the oldest and the most popular of the vacuum tubes. As they are very robust, low cost and highly efficient source of high-power microwaves, they have been a common choice for defence, medical, industrial and commercial applications. This work presents the implementation of a high CW (continuous wave) power 14 vane cavity magnetron operating at 3.7 GHz.
The operation of a basic magnetron involves multiple physics. COMSOL Multiphysics® software proves to be an excellent choice for simulation of magnetron due to its capability to solve for different physics with single and two-way coupling.
As the magnetron cavity is a closed structure, the ‘Electromagnetic Waves, Frequency Domain (emw)’ node is used for obtaining the eigen frequencies of the designed cavity. Due to the thermionic emission of electrons from the cathode, the temperatures inside the cavity reach large values. The authors have used the ‘Heat Transfer in Solids (ht)’ node for the modeling of constant heat discharge from the cathode. This high value of temperatures can lead to stress and deformation of the magnetron structure. Any change in the dimensions of the magnetron cavity will affect its eigen frequencies. The use of ‘Solid mechanics (solid)’ and ‘Moving Mesh (ale)’ physics nodes mimic these effects successfully. The high negative potential between cathode and anode is modeled by ‘Electrostatics (es)’ node. As COMSOL® does not comprise of a direct PIC code, an indirect approach is used with ‘Charge Particle Tracing (cpt)’ module for accurate simulation of the interaction of electrons and the generated electromagnetic fields. Appropriate coupling of the different physics mentioned above and the multiple study step solvers are used the obtain the output power, efficiency of magnetron, temperature rise and physical deformation of the designed magnetron.
