The effect of safety factor profile on transport in steady-state, high-performance scenarios

C. T. Holcomb; J. R. Ferron; T. C. Luce; J. C. Deboo; J. M. Park; A. E. White; F. Turco; T. L. Rhodes; E. J. Doyle; L. Schmitz; M. A. Van Zeeland; G. R. McKee

doi:10.1063/1.3691646

The effect of safety factor profile on transport in steady-state, high-performance scenarios

C. T. Holcomb, J. R. Ferron, T. C. Luce, J. C. Deboo, J. M. Park, A. E. White, F. Turco, T. L. Rhodes, E. J. Doyle, L. Schmitz, M. A. Van Zeeland, G. R. McKee

Plasma Theory and Modeling

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Abstract

An analysis of the dependence of transport on the safety factor profile in high-performance, steady-state scenario discharges is presented. This is based on experimental scans of q 95 and q min taken with fixed N, toroidal field, double-null plasma shape, divertor pumping, and electron cyclotron current drive input. The temperature and thermal diffusivity profiles were found to vary considerably with the q-profile, and these variations were significantly different for electrons and ions. With fixed q 95, both temperature profiles increase and broaden as q min is increased and the magnetic shear becomes low or negative in the inner half radius, but these temperature profile changes are stronger for the electrons. Power balance calculations show the peak in the ion thermal diffusivity ( i) at = 0. 6 - 0. 8 increases with q 95 or q min. In contrast, the peak in the electron diffusivity ( e) decreases as q min is raised from ∼ 1 to 1.5, and it is insensitive to q 95. This is important for fully non-inductive scenario development because it demonstrates that elevated q min and weak or reversed shear allow larger electron temperature gradients and, therefore, increased bootstrap current density to exist at = 0. 6 - 0. 8. Chord-averaged measurements of long wavelength density fluctuation amplitudes (n ) are shown, and these have roughly the same dependence on q-profile as i. This data set provides an opportunity for testing whether theory based transport models can provide insight into the underlying transport physics of high performance scenarios and if they can reproduce observed experimental trends. To this end, we applied the trapped gyro-Landau fluid (TGLF) code to calculate the linear stability of drift waves and found that the resulting variation of growth rates with q-profile are mostly inconsistent with the observed trends of i, e, and n with q-profile. TGLF simulations of the temperature profiles consistent with heating sources also have mixed agreement with the measured profiles, such that the simulated electron and ion heat flux in low q min discharges are too low and heat fluxes in high q min discharges are too high.

Original language	English
Article number	032501
Journal	Physics of Plasmas
Volume	19
Issue number	3
DOIs	https://doi.org/10.1063/1.3691646
State	Published - Mar 2012

Funding

This work was supported by the U.S. Department of Energy under DE-AC52-07NA27344, DE-FC02-04ER54698, DE-AC05-00OR22725, DE-AC05–06OR23100, DE-FG02-08ER54984, and DE-FG02-89ER53296.

Funders	Funder number
U.S. Department of Energy	DE-AC05-00OR22725, DE-AC05–06OR23100, DE-FG02-08ER54984, DE-FC02-04ER54698, DE-AC52-07NA27344, DE-FG02-89ER53296

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@article{3eb463fcb9ba4aeabe5228bb1d014c02,

title = "The effect of safety factor profile on transport in steady-state, high-performance scenarios",

abstract = "An analysis of the dependence of transport on the safety factor profile in high-performance, steady-state scenario discharges is presented. This is based on experimental scans of q 95 and q min taken with fixed N, toroidal field, double-null plasma shape, divertor pumping, and electron cyclotron current drive input. The temperature and thermal diffusivity profiles were found to vary considerably with the q-profile, and these variations were significantly different for electrons and ions. With fixed q 95, both temperature profiles increase and broaden as q min is increased and the magnetic shear becomes low or negative in the inner half radius, but these temperature profile changes are stronger for the electrons. Power balance calculations show the peak in the ion thermal diffusivity ( i) at = 0. 6 - 0. 8 increases with q 95 or q min. In contrast, the peak in the electron diffusivity ( e) decreases as q min is raised from ∼ 1 to 1.5, and it is insensitive to q 95. This is important for fully non-inductive scenario development because it demonstrates that elevated q min and weak or reversed shear allow larger electron temperature gradients and, therefore, increased bootstrap current density to exist at = 0. 6 - 0. 8. Chord-averaged measurements of long wavelength density fluctuation amplitudes (n ) are shown, and these have roughly the same dependence on q-profile as i. This data set provides an opportunity for testing whether theory based transport models can provide insight into the underlying transport physics of high performance scenarios and if they can reproduce observed experimental trends. To this end, we applied the trapped gyro-Landau fluid (TGLF) code to calculate the linear stability of drift waves and found that the resulting variation of growth rates with q-profile are mostly inconsistent with the observed trends of i, e, and n with q-profile. TGLF simulations of the temperature profiles consistent with heating sources also have mixed agreement with the measured profiles, such that the simulated electron and ion heat flux in low q min discharges are too low and heat fluxes in high q min discharges are too high.",

author = "Holcomb, {C. T.} and Ferron, {J. R.} and Luce, {T. C.} and Deboo, {J. C.} and Park, {J. M.} and White, {A. E.} and F. Turco and Rhodes, {T. L.} and Doyle, {E. J.} and L. Schmitz and {Van Zeeland}, {M. A.} and McKee, {G. R.}",

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T1 - The effect of safety factor profile on transport in steady-state, high-performance scenarios

AU - Holcomb, C. T.

AU - Ferron, J. R.

AU - Luce, T. C.

AU - Deboo, J. C.

AU - Park, J. M.

AU - White, A. E.

AU - Turco, F.

AU - Rhodes, T. L.

AU - Doyle, E. J.

AU - Schmitz, L.

AU - Van Zeeland, M. A.

AU - McKee, G. R.

PY - 2012/3

Y1 - 2012/3

N2 - An analysis of the dependence of transport on the safety factor profile in high-performance, steady-state scenario discharges is presented. This is based on experimental scans of q 95 and q min taken with fixed N, toroidal field, double-null plasma shape, divertor pumping, and electron cyclotron current drive input. The temperature and thermal diffusivity profiles were found to vary considerably with the q-profile, and these variations were significantly different for electrons and ions. With fixed q 95, both temperature profiles increase and broaden as q min is increased and the magnetic shear becomes low or negative in the inner half radius, but these temperature profile changes are stronger for the electrons. Power balance calculations show the peak in the ion thermal diffusivity ( i) at = 0. 6 - 0. 8 increases with q 95 or q min. In contrast, the peak in the electron diffusivity ( e) decreases as q min is raised from ∼ 1 to 1.5, and it is insensitive to q 95. This is important for fully non-inductive scenario development because it demonstrates that elevated q min and weak or reversed shear allow larger electron temperature gradients and, therefore, increased bootstrap current density to exist at = 0. 6 - 0. 8. Chord-averaged measurements of long wavelength density fluctuation amplitudes (n ) are shown, and these have roughly the same dependence on q-profile as i. This data set provides an opportunity for testing whether theory based transport models can provide insight into the underlying transport physics of high performance scenarios and if they can reproduce observed experimental trends. To this end, we applied the trapped gyro-Landau fluid (TGLF) code to calculate the linear stability of drift waves and found that the resulting variation of growth rates with q-profile are mostly inconsistent with the observed trends of i, e, and n with q-profile. TGLF simulations of the temperature profiles consistent with heating sources also have mixed agreement with the measured profiles, such that the simulated electron and ion heat flux in low q min discharges are too low and heat fluxes in high q min discharges are too high.

AB - An analysis of the dependence of transport on the safety factor profile in high-performance, steady-state scenario discharges is presented. This is based on experimental scans of q 95 and q min taken with fixed N, toroidal field, double-null plasma shape, divertor pumping, and electron cyclotron current drive input. The temperature and thermal diffusivity profiles were found to vary considerably with the q-profile, and these variations were significantly different for electrons and ions. With fixed q 95, both temperature profiles increase and broaden as q min is increased and the magnetic shear becomes low or negative in the inner half radius, but these temperature profile changes are stronger for the electrons. Power balance calculations show the peak in the ion thermal diffusivity ( i) at = 0. 6 - 0. 8 increases with q 95 or q min. In contrast, the peak in the electron diffusivity ( e) decreases as q min is raised from ∼ 1 to 1.5, and it is insensitive to q 95. This is important for fully non-inductive scenario development because it demonstrates that elevated q min and weak or reversed shear allow larger electron temperature gradients and, therefore, increased bootstrap current density to exist at = 0. 6 - 0. 8. Chord-averaged measurements of long wavelength density fluctuation amplitudes (n ) are shown, and these have roughly the same dependence on q-profile as i. This data set provides an opportunity for testing whether theory based transport models can provide insight into the underlying transport physics of high performance scenarios and if they can reproduce observed experimental trends. To this end, we applied the trapped gyro-Landau fluid (TGLF) code to calculate the linear stability of drift waves and found that the resulting variation of growth rates with q-profile are mostly inconsistent with the observed trends of i, e, and n with q-profile. TGLF simulations of the temperature profiles consistent with heating sources also have mixed agreement with the measured profiles, such that the simulated electron and ion heat flux in low q min discharges are too low and heat fluxes in high q min discharges are too high.

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The effect of safety factor profile on transport in steady-state, high-performance scenarios

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