Measurements of density and potential fluctuations in the Advanced Toroidal Facility using a heavy ion beam probe

Summary form only given. The Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory has been a rewarding device on which to exploit the unique capabilities of a Heavy Ion Beam Probe (HIBP) to measure electric scalar potential, magnetic vector potential, and electron density. Although the time available for aggressive data-taking was quite limited, we have obtained some very interesting information for a variety of discharge conditions. Recently, we have been able to look more carefully at some data which shows a very strong coherent oscillation on top of the normal background fluctuations in density and potential during the ramp-up of neutral beam heating. In this paper, we present a detailed picture of this oscillation showing the evolution of the density and potential fluctuations during neutral beam ramp-up. Changes in plasma operating conditions and signals from other diagnostics that show similar features, or would be expected to show similar features, to what we have seen with the ATF HIBP are also presented.