We describe a new technique to measure the spatial distribution of plasma density fluctuations integrated over both frequency and wave vector. Measurements are reported of the frequencies, wave vectors, amplitudes, and also the spatial distributions of low-frequency density fluctuations present in the alcator tokamak. Two regimes can be identified. In high-density plasmas ($\overline{n}>{10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$) the fluctuations are peaked at the limiter radius with a fluctuation amplitude of $\frac{\tilde{n}}{n}\simeq 1$. At lower densities the fluctuation amplitudes peak in the interior of the plasma with $\frac{\tilde{n}}{n}\simeq 0.07\pm 0.03$.

• Received 7 December 1977

DOI:https://doi.org/10.1103/PhysRevLett.40.400