First data and preliminary experimental results from a new Doppler Backscattering system on the MAST-U spherical tokamak
A new Doppler backscattering (DBS) system, consisting of Q-band and V-band, has been installed and achieved its first data on the MAST-U spherical tokamak. The Q-band and V-band have separate microwave source systems, but share the same optical front-end components. The Q-band and V-band sources simultaneously generate eight (34, 36, 38, 40, 42, 44, 46 and 48 GHz) and seven (52.5, 55, 57.5, 60, 62.5, 65 and 67.5 GHz) fixed frequency probe beams, respectively. These frequencies provide a large range of radial positions from the low-field-side edge plasma to the core, and possibly to the high-field-side edge, depending on the plasma conditions. The quasi-optical system consists of a remotely-tunable polarizer, a focusing lens and a remotely-steerable mirror. By steering the mirror, the system provides remote control of the probed density wavenumber, and the angle of the launched DBS to match the magnetic field pitch angle. The range of accessible density turbulence wavenumbers (k_theta*rho_s) is reasonably large with normalized wavenumber ranging from <0.5 to 9. Additionally, the first data acquired by this DBS system has been analyzed and presented in this paper.