TY - JOUR
T1 - Edge energy transport barrier and turbulence in the I-mode regime on alcator C-mod
AU - Hubbard, A.E.
AU - Whyte, D.G.
AU - Churchill, R.M.
AU - Cziegler, I.
AU - Dominguez, A.
AU - Golfinopoulos, T.
AU - Hughes, J.W.
AU - Rice, J.E.
AU - Greenwald, M.J.
AU - Howard, N.
AU - Lipschultz, B.
AU - Marmar, E.S.
AU - Reinke, M.L.
AU - Terry, J.L.
AU - Bespamyatnov, I.
AU - Rowan, W.L.
PY - 2011/5/1
Y1 - 2011/5/1
N2 - We report extended studies of the I-mode regime Whyte, Nucl. Fusion 50, 105005 (2010) obtained in the Alcator C-Mod tokamak Marmar, Fusion Sci. Technol. 51(3), 3261 (2007). This regime, usually accessed with unfavorable ion B × ∇B drift, features an edge thermal transport barrier without a strong particle transport barrier. Steady I-modes have now been obtained with favorable B × ∇B drift, by using specific plasma shapes, as well as with unfavorable drift over a wider range of shapes and plasma parameters. With favorable drift, power thresholds are close to the standard scaling for L-H transitions, while with unfavorable drift they are ∼ 1.5-3 times higher, increasing with I. Global energy confinement in both drift configurations is comparable to H-mode scalings, while density profiles and impurity confinement are close to those in L-mode. Transport analysis of the edge region shows a decrease in edge , by typically a factor of 3, between L- and I-mode. The decrease correlates with a drop in mid-frequency fluctuations (f ∼ 50-150 kHz) observed on both density and magnetics diagnostics. Edge fluctuations at higher frequencies often increase above L-mode levels, peaking at f ∼ 250 kHz. This weakly coherent mode is clearest and has narrowest width (ff ∼ 0.45) at low q and high T , up to 1 keV. The E well in I-mode is intermediate between L- and H-mode and is dominated by the diamagnetic contribution in the impurity radial force balance, without the V shear typical of H-modes.
AB - We report extended studies of the I-mode regime Whyte, Nucl. Fusion 50, 105005 (2010) obtained in the Alcator C-Mod tokamak Marmar, Fusion Sci. Technol. 51(3), 3261 (2007). This regime, usually accessed with unfavorable ion B × ∇B drift, features an edge thermal transport barrier without a strong particle transport barrier. Steady I-modes have now been obtained with favorable B × ∇B drift, by using specific plasma shapes, as well as with unfavorable drift over a wider range of shapes and plasma parameters. With favorable drift, power thresholds are close to the standard scaling for L-H transitions, while with unfavorable drift they are ∼ 1.5-3 times higher, increasing with I. Global energy confinement in both drift configurations is comparable to H-mode scalings, while density profiles and impurity confinement are close to those in L-mode. Transport analysis of the edge region shows a decrease in edge , by typically a factor of 3, between L- and I-mode. The decrease correlates with a drop in mid-frequency fluctuations (f ∼ 50-150 kHz) observed on both density and magnetics diagnostics. Edge fluctuations at higher frequencies often increase above L-mode levels, peaking at f ∼ 250 kHz. This weakly coherent mode is clearest and has narrowest width (ff ∼ 0.45) at low q and high T , up to 1 keV. The E well in I-mode is intermediate between L- and H-mode and is dominated by the diamagnetic contribution in the impurity radial force balance, without the V shear typical of H-modes.
UR - http://www.scopus.com/inward/record.url?scp=79958809223&partnerID=8YFLogxK
U2 - 10.1063/1.3582135
DO - 10.1063/1.3582135
M3 - Article
AN - SCOPUS:79958809223
SN - 1070-664X
VL - 18
JO - Physics of Plasmas
JF - Physics of Plasmas
IS - 5
ER -