Multi-physics analysis of a 1 MW gyrotron cavity cooled by mini-channels

The interaction cavity of the European 170 GHz, 1 MW Continuous Wave (CW) gyrotron for ITER, which could also be water-cooled using mini-channels as recently proposed, experiences during operation a very large heat load (>15 MW/m(2)) localized on a very short (<1 cm) axial length. Such heat loads are typical for high power gyrotrons. As the thermal deformation of the cavity influences the electromagnetic field structure and consequently the gyrotron operation, the analysis of the cavity performance requires the simultaneous solution of the coupled thermal-hydraulic, thermo-mechanic and electro-magnetic fields. In this paper, the thermal behaviour of the cavity under nominal heat load is computed first by CFD. Then a 3D thermo-mechanical model of the cavity is developed, based on the temperature maps computed by CFD, to evaluate the resulting deformation of the inner cavity surface. Finally the deformation is used to compute the updated heat load coming from the electromagnetic field generated by the electron beam in the deformed cavity, which becomes the input for a new iteration of the thermal-hydraulic, thermal-mechanical and electromagnetic analyses. It is shown that this iterative procedure converges to a self-consistent heat-load/temperature-field/deformation-field picture in nominal operating conditions, without exceeding a temperature of similar to 230 degrees C on the inner surface of the cavity. (C) 2017 Elsevier B.V. All rights reserved.