In this talk measurements of short wavelength (20 cm-1) density fluctuations in the HDH-mode using the localised turbulence scattering (LOTUS) diagnostic are presented. These measurements will be contrasted to fluctuations during normal confinement operation (NC-mode).
The measurements show a consistent increase of the fluctuation level associated with the transition from NC- to HDH-mode. There is a very strong similarity between the global parameters of the HDH-mode and the enhanced D-alpha H-mode (EDA H-mode) found in the Alcator C-Mod tokamak. This motivates us to make a comparative analysis of the fluctuation behaviour in these two improved confinement regimes to determine whether the two are identical modes.