Modeling of mode competition in gyrotrons with coaxial cavities by using magy

Abstract

Summary form only given. Gyrotrons with coaxial cavities are very promising sources of high power short millimeter wavelength radiation for plasma heating and current drive in control fusion applications. Recent experimental studies of coaxial gyrotrons have shown that up to two Megawatt of output power in region of 165-170 GHz can be achieved. However, the coaxial gyrotrons are very complex devices for design because of presence of a tapered azimuthally corrugated inner conductor in order to provide mode selection. The design of high power gyrotrons with coaxial cavities requires a lot of computational efforts. The major challenge for coaxial gyrotrons design is to predict accurately mode competition in complex coaxial cavities and avoid spurious mode excitation. MAGY (MAryland GYrotron) is very effective design code used in the past by the US vacuum electronic industry to design high power gyrotrons for fusion applications. Recently MAGY has been developed to be suitable for accurate and efficient simulation of gyrotrons with coaxial cavities. The MAGY model includes a self-consistent, nonlinear solution of the three-dimensional equations of motion of electrons and the solution of the time-dependent field equations. The effect of azimuthally corrugations at inner conductor on electromagnetic fields is described by equivalent surface impedances. The extended MAGY model allows predicting properties of modes of complex coaxial structures. The modified code has been validated by comparison of simulations results with the results of experimental measurements presented. The calculated dependence of the output power on beam voltage agrees with the results of measurements