Measurements of fluctuations and space potential profiles in the Texas Experimental Tokamak (TEXT)

A Heavy Ion Beam Probe (HIBP) has been used to measure density and space potential fluctuations, and the space potential profile in TEXT. Part A presents the fluctuation data with emphasis on poloidal variations. Space potential profiles are discussed in Part B. TEXT is a non-divertor tokamak with a major radius of R=1 m and a minor radius of a=0.26 m. The results presented are for ohmic heated discharges. This HIBP on TEXT consists of injecting singly charged thallium ions into the plasma with ion energies up to 540 kev. Doubly charged ions, produced dominantly be electron impact ionization, are detected using an electrostatic energy analyzer. The change in ion energy is a measure of the space potential, and normalized variations of the detected current are a measure of density fluctuations. The density and potential fluctuations are simultaneously measured at up to three spatial locations, this allow evaluation of the phase angle and coherence between the fluctuations, as well as estimates of wave numbers. (author) 6 refs., 4 figs