Fast ion collective Thomson scattering diagnostic for ITER - Progress of design

In the era of high power and burning plasma fusion experiments with significant populations of fast particles, the diagnosis of fast ion dynamics becomes an important topic. In ITER, populations of fast ions due to ICRH and NBI, as well as fusion born alphas will carry a significant fraction of the free energy of the plasma. This may affect instabilities and transport in the plasma. A key candidate for diagnosing confined fast ions in ITER is the technique of collective Thomson scattering (CTS). A fast ion CTS system with a probing frequency of 60 GHz has been proposed for ITER. Based on diagnostic experience from particularly TEXTOR and ASDEX Upgrade, work is now progressing towards a final design of a fast ion CTS diagnostic for ITER. The biggest challenge of the diagnostic design is the HFS receiver located in the restricted space behind the blanket modules. Calculations and a series of mock-up measurements have brought the design towards a four mirror quasi-optical solution. The development as well as the present design will be presented.