Mechanical design of the two dimensional beam emission spectroscopy diagnostics on mast

A two dimensional beam emission spectroscopy (BES) system optimized for density turbulence measurements has recently been installed on the MAST tokamak. This system observes the emission of a Deuterium heating beam using a rotatable mirror to view from the plasma centre to the outboard edge (0.7–1.5 m), although the optics is optimized for core region (1.2 m). The beam is imaged onto a 4×8 pixel Avalanche Photodiode (APD) array detector, enabling measurements with 1 MHz bandwidth at photon-flux level of few times 1011 photons/s. This article will present the mechanical design of MAST BES equipment with special emphasis on its in-vessel components.