Non-neoclassical up/down asymmetry of impurity emission on Alcator C-Mod
Author(s)Reinke, Matthew Logan; Rice, John E.; Hutchinson, Ian H.; Greenwald, Martin J.; Howard, Nathaniel Thomas; Hughes, Jerry W.; Irby, James Henderson; Podpaly, Yuri; Terry, James L.; White, Anne E.; ... Show more Show less
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We demonstrate that existing theories are insufficient to explain up/down asymmetries of argon x-ray emission in Alcator C-Mod ohmic plasmas. Instead of the poloidal variation, ñ[subscript z]/〈n[subscript z]〉, being of order the inverse aspect ratio, ϵ, and scaling linearly with B[subscript t][superscript _ over n][subscript e]/I[2 over p], it is observed over 0.8 < r/a < 1.0 to be of order unity and exhibits a threshold behaviour between 3.5 <B[subscript t][superscript _ over n][subscript e]/I[subscript p] < 4.0 (T10[superscript 20] m[superscript −3] MA[superscript −1]). The transition from a poloidally symmetric to asymmetric impurity distribution is shown to occur at densities just below those that trigger a reversal of the core toroidal rotation direction, thought to be linked to the transition between the linear and saturated ohmic confinement regimes. A possible drive is discussed by which anomalous radial transport might sustain the impurity density asymmetry as the ratio of the perpendicular to parallel equilibration times, τ[subscript ⊥,z]/τ[subscript ∥,z], approaches unity. This explanation requires a strong up/down asymmetry in radial flux which, while not observable on C-Mod, has been measured in TEXT and Tore Supra ohmic plasmas.
DepartmentMassachusetts Institute of Technology. Department of Nuclear Science and Engineering; Massachusetts Institute of Technology. Plasma Science and Fusion Center
Reinke, M.L., J.E. Rice, I.H. Hutchinson, M. Greenwald, N.T. Howard, J.W. Hughes, J. Irby, Y. Podpaly, J.L. Terry, and A. White. “Non-neoclassical up/down asymmetry of impurity emission on Alcator C-Mod.” Nuclear Fusion 53, no. 4 (April 1, 2013): 043006.
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