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

The interaction cavity of the European 170 GHz, 1 MW Continuous Wave (CW) gyrotron for ITER, whichcould also be water-cooled using mini-channels as recently proposed, experiences during operation avery large heat load (>15 MW/m2) localized on a very short (<1 cm) axial length. Such heat loads aretypical for high power gyrotrons.As the thermal deformation of the cavity influences the electromagnetic field structure and con-sequently the gyrotron operation, the analysis of the cavity performance requires the simultaneoussolution 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 3Dthermo-mechanical model of the cavity is developed, based on the temperature maps computed byCFD, to evaluate the resulting deformation of the inner cavity surface. Finally the deformation is usedto compute the updated heat load coming from the electromagnetic field generated by the electronbeam 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 toa self-consistent heat-load/temperature-field/deformation-field picture in nominal operating conditions,without exceeding a temperature of ∼230◦C on the inner surface of the cavity.