Simultaneous measurements of density and potential fluctuation with heavy ion beam probe in the Compact Helical System

Density and potential fluctuations are simultaneously measured, using a heavy ion beam probe, in electron cyclotron resonance heated plasmas of the Compact Helical System. The spectra of density and potential fluctuations are presented with radial profiles of these fluctuation amplitudes. Local density fluctuations are evaluated by removing the path integral effect under the simplest assumption that the correlation length of the fluctuations is infinitesimally short.