Time-domain triple-probe measurement of edge plasma turbulence on the Texas Experimental Tokamak Upgrade

The time-domain triple-probe method (TDTP) switches Langmuir probe states at high speeds to gather triple-probe information thereby avoiding errors which result when implementing the triple-probe method with spatially separated single state probes in an inhomogeneous plasma. Successful implementation of the TDTP method requires a switching frequency greater than the turbulence bandwidth so that aliased power does not degrade time interpolated estimates of triple-probe states. Additionally, transients between states, largely determined by the ratio of ion saturation current to probe capacitance, must be short enough to establish a probe endash plasma equilibrium. These requirements have been met in the edge plasma and parts of the scrape-off layer on the Texas Experimental Tokamak Upgrade. Temperature fluctuations have been measured at two poloidally separated probes. Cross-phase and coherence spectra consistent with those of floating potential fluctuations and ion saturation current fluctuations are measured. copyright 1997 American Institute of Physics