High-sensitivity, high-resolution measurements of radiated power on TEXT-U

Investigations of a possible radiation drive of edge turbulence in tokamaks require sensitive radiated power measurements having high temporal and spatial resolution. The authors use a commercially available 16-element X-UV-enhanced photodiode array having essentially 100% quantum efficiency from ∼ 25 eV to ≥ 6 keV. The frequency response is presently limited by the amplifiers to ∼ 50 kHz, although the ultimate response is expected to be much higher (>200 kHz). Each element's view is ∼ 0.4 cm wide along the major radius at the plasma midplane while the view of the entire array is ∼ 6.3 cm wide and is scannable over the entire plasma cross section. The details of the system as well as observations of fine spatial structures and fluctuations undetectable by conventional bolometers are presented