TY - JOUR
T1 - Ion temperature profile stiffness
T2 - Non-linear gyrokinetic simulations and comparison with experiment
AU - Citrin, J.
AU - Jenko, F.
AU - Mantica, P.
AU - Told, D.
AU - Bourdelle, C.
AU - Dumont, R.
AU - Garcia, J.
AU - Haverkort, J. W.
AU - Hogeweij, G. M.D.
AU - Johnson, T.
AU - Pueschel, M. J.
PY - 2014/2/1
Y1 - 2014/2/1
N2 - Recent experimental observations at JET show evidence of reduced ion temperature profile stiffness. An extensive set of nonlinear gyrokinetic simulations are performed based on the experimental discharges, investigating the physical mechanism behind the observations. The impact on the ion heat flux of various parameters that differ within the data-set are explored. These parameters include the safety factor, magnetic shear, toroidal flow shear, effect of rotation on the magnetohydrodynamic equilibrium, R/Ln, βe, Zeff, Te/Ti, and the fast-particle content. While previously hypothesized to be an important factor in the stiffness reduction, the combined effect of toroidal flow shear and low magnetic shear is not predicted by the simulations to lead to a significant reduction in ion heat flux, due both to an insufficient magnitude of flow shear and significant parallel velocity gradient destabilization. It is however found that nonlinear electromagnetic effects due to both thermal and fast-particle pressure gradients, even at low βe, can significantly reduce the ion heat flux, and is a key factor in explaining the experimental observations. A total of four discharges are examined, at both inner and outer radii. For all cases studied, the simulated and experimental ion heat flux values agree within reasonable variations of input parameters around the experimental uncertainties.
AB - Recent experimental observations at JET show evidence of reduced ion temperature profile stiffness. An extensive set of nonlinear gyrokinetic simulations are performed based on the experimental discharges, investigating the physical mechanism behind the observations. The impact on the ion heat flux of various parameters that differ within the data-set are explored. These parameters include the safety factor, magnetic shear, toroidal flow shear, effect of rotation on the magnetohydrodynamic equilibrium, R/Ln, βe, Zeff, Te/Ti, and the fast-particle content. While previously hypothesized to be an important factor in the stiffness reduction, the combined effect of toroidal flow shear and low magnetic shear is not predicted by the simulations to lead to a significant reduction in ion heat flux, due both to an insufficient magnitude of flow shear and significant parallel velocity gradient destabilization. It is however found that nonlinear electromagnetic effects due to both thermal and fast-particle pressure gradients, even at low βe, can significantly reduce the ion heat flux, and is a key factor in explaining the experimental observations. A total of four discharges are examined, at both inner and outer radii. For all cases studied, the simulated and experimental ion heat flux values agree within reasonable variations of input parameters around the experimental uncertainties.
KW - electromagnetic turbulence
KW - gyrokinetic simulation
KW - tokamak transport
UR - http://www.scopus.com/inward/record.url?scp=84893477025&partnerID=8YFLogxK
U2 - 10.1088/0029-5515/54/2/023008
DO - 10.1088/0029-5515/54/2/023008
M3 - Article
AN - SCOPUS:84893477025
SN - 0029-5515
VL - 54
JO - Nuclear Fusion
JF - Nuclear Fusion
IS - 2
M1 - 023008
ER -