In-Vessel Mirrors for the MAST-U EBW System

UKAEA is installing an Electron Bernstein Wave (EBW) system on MAST-U, which aims at injecting two dual-frequency (28GHz and 34.8GHz) microwave beams each of up to 900kW and pulse duration of 4.5s. There are eight 1 OFF in-vessel copper-coated graphite mirrors. The primary function of the in-vessel mirrors is to redirect the microwaves, produced by the gyrotron, and direct these into the plasma. The main microwave mirror face has a curved profile, providing focusing of the beam. The curved profile is defined using an ellipsoid shape. These mirror faces absorb a small percentage of the microwaves. These absorbed microwaves act as a heat flux on the mirror face in a gaussian distribution, peaking at 750kW/m2. A uniform radiative plasma load of 210kW/m2 also acts on all faces excluding the mirror face.